Patent Publication Number: US-2023148324-A1

Title: Organic light emitting diode and organic light emitting device including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2021-0133077, filed in the Republic of Korea on Oct. 7, 2021, which is expressly incorporated by reference into the present application. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to an organic light emitting diode, and more specifically, to an organic light emitting diode having excellent luminous efficiency and luminous lifespan and an organic light emitting device including the organic light emitting diode. 
     Discussion of the Related Art 
     An organic light emitting diode (OLED) display among a flat display device used widely has come into the spotlight as a display device replacing rapidly a liquid crystal display device (LCD). The OLED can be formed as a thin organic film with a thickness less than 2000 Å and can implement unidirectional or bidirectional images by electrode configurations. Also, the OLED can be formed even on a flexible transparent substrate such as a plastic substrate so that a flexible or a foldable display device can be realized with ease using the OLED. In addition, the OLED can be driven at a lower voltage and the OLED has excellent high color purity compared to the LCD. 
     The OLED includes an anode, a cathode and an emitting material layer, and the emitting material layer includes a host and a dopant (e.g., an emitter). 
     Since a fluorescent material as the dopant uses only singlet exciton energy in the luminous process, the related art fluorescent material shows low luminous efficiency. On the contrary, a phosphorescent material can show high luminous efficiency since it uses triplet exciton energy as well as singlet exciton energy in the luminous process. However, metal complex, representative phosphorescent material, has short luminous lifespan for commercial use. 
     In addition, the luminous efficiency and the luminous lifespan of the OLED are affected by the exciton generation efficiency in the host and the energy transfer efficiency from the host to the dopant. 
     Accordingly, development of materials of the emitting material layer being capable of improving the luminous efficiency and the luminous lifespan of the OLED is required. 
     SUMMARY OF THE DISCLOSURE 
     Accordingly, embodiments of the present disclosure are directed to an OLED and an organic light emitting device that substantially obviate one or more of the problems associated with the limitations and disadvantages of the related art. 
     An aspect of the present disclosure is to provide an OLED and an organic light emitting device having excellent luminous efficiency and luminous lifespan. 
     Additional features and aspects will be set forth in the description that follows, and in part will be apparent from the description, or can be learned by practice of the inventive concepts provided herein. Other features and aspects of the inventive concept can be realized and attained by the structure particularly pointed out in the written description, or derivable therefrom, and the claims hereof as well as the appended drawings. 
     To achieve these and other aspects of the inventive concepts, as embodied and broadly described, in one aspect, the present disclosure provides an organic light emitting diode comprising: a first electrode; a second electrode facing the first electrode; and a first emitting part including a first red emitting material layer and positioned between the first and second electrodes, wherein the first red emitting material layer includes a first compound, a second compound and a third compound, wherein the first compound is represented by Formula 1-1: [Formula 1-1] 
     
       
         
         
             
             
         
       
     
     wherein M is molybdenum (Mo), tungsten (W), rhenium (Re), ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt) or silver (Ag); each of A and B is a carbon atom; R is an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group or an unsubstituted or substituted C 3 -C 30  hetero aromatic group; each of X 1  to X 11  is independently a carbon atom, CR 1  or N; only one of: a ring (a) with X 3 -X 5 , Y 1  and A; or a ring (b) with X 8 -X 11 , Y 2  and B is formed; and if the ring (a) is formed, each of X 3  and Y 1  is a carbon atom, X 6  and X 7  or X 7  and X 8  forms an unsubstituted or substituted C 3 -C 30  alicyclic ring, an unsubstituted or substituted C 3 -C 30  hetero alicyclic ring, an unsubstituted or substituted C 6 -C 30  aromatic ring or an unsubstituted or substituted C 3 -C 30  hetero aromatic ring; and Y 2  is BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te, TeO 2 , or NR a , wherein R a  is an unsubstituted or substituted C 1 -C 20  alkyl group or an unsubstituted or substituted C 6 -C 30  aromatic group; if the ring (b) is forms, each of X 8  and Y 2  is a carbon atom, X 1  and X 2  or X 2  and X 3  forms an unsubstituted or substituted C 3 -C 30  alicyclic ring, an unsubstituted or substituted C 3 -C 30  hetero alicyclic ring, an unsubstituted or substituted C 6 -C 30  aromatic ring or an unsubstituted or substituted C 3 -C 30  hetero aromatic ring; and Y 1  is BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te, TeO 2 , or NR a , wherein R a  is an unsubstituted or substituted C 1 -C 20  alkyl group or an unsubstituted or substituted C 6 -C 30  aromatic group, each of R 1  to R 3  is independently hydrogen, protium, deuterium, tritium, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrozone group, an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 2 -C 20  alkenyl group, an unsubstituted or substituted C 2 -C 20  alkynyl group, an unsubstituted or substituted C 1 -C 20  alkoxy group, an amino group, an unsubstituted or substituted C 1 -C 20  alkyl amino group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, a carboxyl group, a nitrile group, an isonitrile group, a sulfanyl group, a phosphino group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group or an unsubstituted or substituted C 3 -C 30  hetero aromatic group, optionally, two adjacent R 1 , and/or R 2  and R 3  form an unsubstituted or substituted C 3 -C 30  alicyclic ring, an unsubstituted or substituted C 3 -C 30  hetero alicyclic ring, an unsubstituted or substituted C 6 -C 30  aromatic ring or an unsubstituted or substituted C 3 -C 30  hetero aromatic ring; 
     
       
         
         
             
             
         
       
     
     is an auxiliary ligand; m is an integer of 1 to 3; n is an integer of 0 to 2; and m+n is an oxidation number of M, wherein the second compound is represented by Formula 2-1: 
     
       
         
         
             
             
         
       
     
     wherein one of X 12  and X 13  is a nitrogen atom (N), and the other one of X 12  and X 13  is an oxygen atom (O) or a sulfur atom (S); each of R 4 , R 5  and R 6  is independently selected from the group consisting of an unsubstituted or substituted C 6 -C 30  aryl group and an unsubstituted or substituted C 3 -C 30  heteroaryl group; and L is selected from the group consisting of an unsubstituted or substituted C 6 -C 30  arylene group and an unsubstituted or substituted C 3 -C 30  heteroarylene group; and a is 0 or 1, wherein the third compound is represented by Formula 3-1: 
     
       
         
         
             
             
         
       
     
     wherein X is NR 8 , O or S, R 8  is selected from the group consisting of an unsubstituted or substituted C 1 -C 10  alkyl group, an unsubstituted or substituted C 6 -C 30  aryl group and an unsubstituted or substituted C 3 -C 30  heteroaryl group, and R 7  is selected from the group consisting of an unsubstituted or substituted C 6 -C 30  aryl group and an unsubstituted or substituted C 3 -C 30  heteroaryl group. 
     In another aspect, the present disclosure provides an organic light emitting device comprising a substrate; and the above organic light emitting diode positioned on or over the substrate. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the inventive concepts as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure, are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain principles of the disclosure. 
         FIG.  1    is a schematic circuit diagram illustrating an organic light emitting display device according to an embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view illustrating an organic light emitting display device according to a first embodiment of the present disclosure. 
         FIG.  3    is a cross-sectional view illustrating an OLED according to a second embodiment of the present disclosure. 
         FIG.  4    is a cross-sectional view illustrating an OLED according to a third embodiment of the present disclosure. 
         FIG.  5    is a cross-sectional view illustrating an organic light emitting display device according to a fourth embodiment of the present disclosure. 
         FIG.  6    is a cross-sectional view illustrating an OLED according to a fifth embodiment of the present disclosure. 
         FIG.  7    is a cross-sectional view illustrating an OLED according to a sixth embodiment of the present disclosure. 
         FIG.  8    is a cross-sectional view illustrating an OLED according to a seventh embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to aspects of the disclosure, examples of which are illustrated in the accompanying drawings. 
     In the present disclosure, a dopant (e.g., an emitter), an n-type host and a p-type host each having excellent optical property are included in an emitting material layer (EML) of an OLED so that the OLED has advantages in at least one of a driving voltage, a luminous efficiency and a luminous lifespan. For example, the organic light emitting device can be an organic light emitting display device or an organic light emitting lighting device. The explanation below is focused on the organic light emitting display device including the OLED. All the components of each OLED and each organic light emitting display device according to all embodiments of the present disclosure are operatively coupled and configured. 
       FIG.  1    is a schematic circuit diagram illustrating an organic light emitting display device according to the present disclosure. 
     As shown in  FIG.  1   , an organic light emitting display device includes a gate line GL, a data line DL, a power line PL, a switching thin film transistor TFT Ts, a driving TFT Td, a storage capacitor Cst, and an OLED D. The gate line GL and the data line DL cross each other to define a pixel region P. The pixel region can include a red pixel region, a green pixel region and a blue pixel region. 
     The switching TFT Ts is connected to the gate line GL and the data line DL, and the driving TFT Td and the storage capacitor Cst are connected to the switching TFT Ts and the power line PL. The OLED D is connected to the driving TFT Td. 
     In the organic light emitting display device, when the switching TFT Ts is turned on by a gate signal applied through the gate line GL, a data signal from the data line DL is applied to the gate electrode of the driving TFT Td and an electrode of the storage capacitor Cst. 
     When the driving TFT Td is turned on by the data signal, an electric current is supplied to the OLED D from the power line PL. As a result, the OLED D emits light. In this case, when the driving TFT Td is turned on, a level of an electric current applied from the power line PL to the OLED D is determined such that the OLED D can produce a gray scale. 
     The storage capacitor Cst serves to maintain the voltage of the gate electrode of the driving TFT Td when the switching TFT Ts is turned off. Accordingly, even if the switching TFT Ts is turned off, a level of an electric current applied from the power line PL to the OLED D is maintained to next frame. 
     As a result, the organic light emitting display device displays a desired image. 
       FIG.  2    is a schematic cross-sectional view of an organic light emitting display device according to a first embodiment of the present disclosure. 
     As shown in  FIG.  2   , an organic light emitting display device  100  includes a substrate  110 , a TFT Tr on or over the substrate  110 , a planarization layer  150  covering the TFT Tr and an OLED D on the planarization layer  150  and connected to the TFT Tr. 
     The substrate  110  can be a glass substrate or a flexible substrate. For example, the flexible substrate can be one of a polyimide (PI) substrate, a polyethersulfone (PES) substrate, a polyethylenenaphthalate (PEN) substrate, a polyethylene terephthalate (PET) substrate and a polycarbonate (PC) substrate. 
     A buffer layer  122  is formed on the substrate, and the TFT Tr is formed on the buffer layer  122 . The buffer layer  122  can be omitted. For example, the buffer layer  122  can be formed of an inorganic insulating material, e.g., silicon oxide or silicon nitride. 
     A semiconductor layer  120  is formed on the buffer layer  122 . The semiconductor layer  120  can include an oxide semiconductor material or polycrystalline silicon. 
     When the semiconductor layer  120  includes the oxide semiconductor material, a light-shielding pattern can be formed under the semiconductor layer  120 . The light to the semiconductor layer  120  is shielded or blocked by the light-shielding pattern such that thermal degradation of the semiconductor layer  120  can be prevented. On the other hand, when the semiconductor layer  120  includes polycrystalline silicon, impurities can be doped into both sides of the semiconductor layer  120 . 
     A gate insulating layer  124  of an insulating material is formed on the semiconductor layer  120 . The gate insulating layer  124  can be formed of an inorganic insulating material such as silicon oxide or silicon nitride. 
     A gate electrode  130 , which is formed of a conductive material, e.g., metal, is formed on the gate insulating layer  124  to correspond to a center of the semiconductor layer  120 . In  FIG.  2   , the gate insulating layer  124  is formed on an entire surface of the substrate  110 . Alternatively, the gate insulating layer  124  can be patterned to have the same shape as the gate electrode  130 . 
     An interlayer insulating layer  132  of an insulating material is formed on the gate electrode  130  and over an entire surface of the substrate  110 . The interlayer insulating layer  132  can be formed of an inorganic insulating material, e.g., silicon oxide or silicon nitride, or an organic insulating material, e.g., benzocyclobutene or photo-acryl. 
     The interlayer insulating layer  132  includes first and second contact holes  134  and  136  exposing both sides of the semiconductor layer  120 . The first and second contact holes  134  and  136  are positioned at both sides of the gate electrode  130  to be spaced apart from the gate electrode  130 . 
     The first and second contact holes  134  and  136  are formed through the gate insulating layer  124 . Alternatively, when the gate insulating layer  124  is patterned to have the same shape as the gate electrode  130 , the first and second contact holes  134  and  136  is formed only through the interlayer insulating layer  132 . 
     A source electrode  144  and a drain electrode  146 , which are formed of a conductive material, e.g., metal, are formed on the interlayer insulating layer  132 . 
     The source electrode  144  and the drain electrode  146  are spaced apart from each other with respect to the gate electrode  130  and respectively contact both sides of the semiconductor layer  120  through the first and second contact holes  134  and  136 . 
     The semiconductor layer  120 , the gate electrode  130 , the source electrode  144  and the drain electrode  146  constitute the TFT Tr. The TFT Tr serves as a driving element. Namely, the TFT Tr is the driving TFT Td (of  FIG.  1   ). 
     In the TFT Tr, the gate electrode  130 , the source electrode  144 , and the drain electrode  146  are positioned over the semiconductor layer  120 . Namely, the TFT Tr has a coplanar structure. 
     Alternatively, in the TFT Tr, the gate electrode can be positioned under the semiconductor layer, and the source and drain electrodes can be positioned over the semiconductor layer such that the TFT Tr can have an inverted staggered structure. In this instance, the semiconductor layer can include amorphous silicon. 
     The gate line and the data line cross each other to define the pixel region, and the switching TFT is formed to be connected to the gate and data lines. The switching TFT is connected to the TFT Tr as the driving element. In addition, the power line, which can be formed to be parallel to and spaced apart from one of the gate and data lines, and the storage capacitor for maintaining the voltage of the gate electrode of the TFT Tr in one frame can be further formed. 
     A planarization layer  150  is formed on an entire surface of the substrate  110  to cover the source and drain electrodes  144  and  146 . The planarization layer  150  provides a flat top surface and has a drain contact hole  152  exposing the drain electrode  146  of the TFT Tr. 
     The OLED D is disposed on the planarization layer  150  and includes a first electrode  160 , which is connected to the drain electrode  146  of the TFT Tr through the drain contact hole  152 , an organic light emitting layer  162  and a second electrode  164 . The organic light emitting layer  162  and the second electrode  164  are sequentially stacked on the first electrode  160 . For example, a red pixel region, a green pixel region and a blue pixel region can be defined on the substrate  110 , and the OLED D is positioned in each of the red, green and blue pixel regions. Namely, the OLEDs respectively emitting the red, green and blue light are respectively positioned in each of the red, green and blue pixel regions. 
     A first electrode  160  is separately formed in each pixel and on the planarization layer  150 . The first electrode  160  can be an anode and can be formed of a conductive material, e.g., a transparent conductive oxide (TCO), having a relatively high work function. For example, the first electrode  160  can be formed of indium-tin-oxide (ITO), indium-zinc-oxide (IZO), indium-tin-zinc-oxide (ITZO), tin oxide (SnO), zinc oxide (ZnO), indium-copper-oxide (ICO) or aluminum-zinc-oxide (Al:ZnO, AZO). 
     When the organic light emitting display device  100  is operated in a bottom-emission type, the first electrode  160  can have a single-layered structure of the transparent conductive material layer. When the organic light emitting display device  100  is operated in a top-emission type, the first electrode  160  can further include a reflection electrode or a reflection layer. For example, the reflection electrode or the reflection layer can be formed of silver (Ag) or aluminum-palladium-copper (APC) alloy. In the top-emission type organic light emitting display device  100 , the first electrode  160  can have a triple-layered structure of ITO/Ag/ITO or ITO/APC/ITO. 
     A bank layer  166  is formed on the planarization layer  150  to cover an edge of the first electrode  160 . Namely, the bank layer  166  is positioned at a boundary of the pixel and exposes a center of the first electrode  160  in the pixel. 
     The organic emitting layer  162  is formed on the first electrode  160 . The organic emitting layer  162  can have a single-layered structure of an emitting material layer. Alternatively, the organic emitting layer  162  can further include at least one of a hole injection layer (HIL), a hole transporting layer (HTL), an electron blocking layer (EBL), a hole blocking layer (HBL), an electron transporting layer (ETL) and an electron injection layer (EIL) to have a multi-layered structure. In addition, the organic emitting layer  162  can include at least two EMLs, which is spaced apart from each other, to have a tandem structure. 
     As illustrated below, in the OLED D in the red pixel region, the EML in the organic emitting layer  162  includes a first compound being a red dopant (emitter), a second compound being a p-type host and a third compound being an n-type host. As a result, in the OLED D, the driving voltage is decreased, and the luminous efficiency and the luminous lifespan are increased. 
     The second electrode  164  is formed over the substrate  110  where the organic emitting layer  162  is formed. The second electrode  164  covers an entire surface of the display area and can be formed of a conductive material having a relatively low work function to serve as a cathode. For example, the second electrode  164  can be formed of aluminum (Al), magnesium (Mg), calcium (Ca), silver (Ag) or their alloy or combination. In the top-emission type organic light emitting display device  100 , the second electrode  164  can have a thin profile (small thickness) to provide a light transmittance property (or a semi-transmittance property). 
     The organic light emitting display device  100  can further include a color filter corresponding to the red, green and blue pixel regions. For example, red, green and blue color filter patterns can be formed in the red, green and blue pixel regions, respectively, so that the color purity of the organic light emitting display device  100  can be improved. In the bottom-type organic light emitting display device  100 , the color filter can be disposed between the OLED D and the substrate  110 , e.g., between the interlayer insulating layer  132  and the planarization layer  150 . Alternatively, in the top-emission type organic light emitting display device  100 , the color filter can be disposed on or over the OLED D, e.g., on or over the second electrode  164 . 
     An encapsulation film  170  is formed on the second electrode  164  to prevent penetration of moisture into the OLED D. The encapsulation film  170  includes a first inorganic insulating layer  172 , an organic insulating layer  174  and a second inorganic insulating layer  176  sequentially stacked, but it is not limited thereto. The encapsulation film  170  can be omitted. 
     The organic light emitting display device  100  can further include a polarization plate for reducing an ambient light reflection. For example, the polarization plate can be a circular polarization plate. In the bottom-emission type organic light emitting display device  100 , the polarization plate can be disposed under the substrate  110 . In the top-emission type organic light emitting display device  100 , the polarization plate can be disposed on or over the encapsulation film  170 . 
     In addition, in the top-emission type organic light emitting display device  100 , a cover window can be attached to the encapsulation film  170  or the polarization plate. In this instance, the substrate  110  and the cover window have a flexible property such that a flexible organic light emitting display device can be provided. 
       FIG.  3    is a cross-sectional view illustrating an OLED according to a second embodiment of the present disclosure. 
     As shown in  FIG.  3   , the OLED D1 includes the first and second electrodes  160  and  164  facing each other and the organic emitting layer  162  therebetween. The organic emitting layer  162  includes a red EML  230 . 
     The organic light emitting display device  100  (of  FIG.  2   ) includes the red, green and blue pixel regions, and the OLED D1 can be positioned in the red pixel region. 
     The first electrode  160  is an anode for injecting the hole, and the second electrode  164  is a cathode for injecting the electron. One of the first and second electrodes  160  and  164  is a reflective electrode, and the other one of the first and second electrodes  160  and  164  is a transparent (semitransparent) electrode. 
     For example, the first electrode  160  can include a transparent conductive material, e.g., ITO or IZO, and the second electrode  164  can include one of Al, Mg, Ag, AlMg and MgAg. 
     The organic emitting layer  162  can further include at least one of the HTL  220  under the red EML  230  and the ETL  240  on or over the red EML  230 . Namely, the HTL  220  is disposed between the red EML  230  and the first electrode  160 , and the ETL  240  is disposed between the red EML  230  and the second electrode  164 . 
     In addition, the organic emitting layer  162  can further include at least one of the HIL  210  under the HTL  220  and the EIL  250  on the ETL  240 . 
     The organic emitting layer  162  can further include at least one of the EBL between the HTL  220  and the red EML  230  and the HBL between the ETL  240  and the red EML  230 . 
     In the OLED D1 of the present disclosure, the red EML  230  can constitute an emitting part, or the red EML  230  and at least one of the HIL  210 , the HTL  220 , the EBL, the HBL, the ETL  240  and the EIL  250  can constitute the emitting part. 
     The red EML  230  includes a first compound  232  being the red dopant, a second compound  234  being the p-type host, e.g., a first host, and a third compound  236  being the n-type host, e.g., a second host. The red EML can have a thickness of 100 to 400 Å, e.g., 200 to 400 Å. 
     In the red EML  230 , each of the second and third compounds  234  and  236  can have a weight % being greater than the first compound  232 . For example, in the red EML  230 , the first compound  232  can have a weight % of 1 to 20, e.g., 5 to 15. 
     In addition, in the red EML  230 , a ratio of the weight % between the second compound  234  and the third compound  236  can be 1:3 to 3:1. For example, in the red EML  230 , the second and third compounds  234  and  236  can have the same weight %. 
     The first compound  232  is represented by Formula 1-1. The first compound  232  is an organometallic compound and has a rigid chemical conformation so that it can enhance luminous efficiency and luminous lifespan of the OLED D1. 
     
       
         
         
             
             
         
       
     
     wherein 
     M is molybdenum (Mo), tungsten (W), rhenium (Re), ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt) or silver (Ag); 
     each of A and B is a carbon atom; 
     R is an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group or an unsubstituted or substituted C 3 -C 30  hetero aromatic group; 
     each of X 1  to X 11  is independently a carbon atom, CR 1  or N; 
     only one of: a ring (a) with X 3 -X 5 , Y 1  and A; or a ring (b) with X 8 -X 11 , Y 2  and B, is formed; and 
     if the ring (a) is formed,
         each of X 3  and Y 1  is a carbon atom,   X 6  and X 7  or X 7  and X 8  forms an unsubstituted or substituted C 3 -C 30  alicyclic ring, the unsubstituted or substituted C 3 -C 30  hetero alicyclic ring, an unsubstituted or substituted C 6 -C 30  aromatic ring or an unsubstituted or substituted C 3 -C 30  hetero aromatic ring; and   Y 2  is BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te, TeO 2 , or NR a , wherein R a  is an unsubstituted or substituted C 1 -C 20  alkyl group or an unsubstituted or substituted C 6 -C 30  aromatic group;       

     if the ring (b) is forms,
         each of X 8  and Y 2  is a carbon atom,   X 1  and X 2  or X 2  and X 3  forms an unsubstituted or substituted C 3 -C 30  alicyclic ring, an unsubstituted or substituted C 3 -C 30  hetero alicyclic ring, an unsubstituted or substituted C 6 -C 30  aromatic ring or an unsubstituted or substituted C 3 -C 30  hetero aromatic ring; and   Y 1  is BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te, TeO 2 , or NR a , wherein R a  is an unsubstituted or substituted C 1 -C 20  alkyl group or an unsubstituted or substituted C 6 -C 30  aromatic group,       

     each of R 1  to R 3  is independently hydrogen, protium, deuterium, tritium, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrozone group, an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 2 -C 20  alkenyl group, an unsubstituted or substituted C 2 -C 20  alkynyl group, an unsubstituted or substituted C 1 -C 20  alkoxy group, an amino group, an unsubstituted or substituted C 1 -C 20  alkyl amino group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, a carboxyl group, a nitrile group, an isonitrile group, a sulfanyl group, a phosphino group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group or an unsubstituted or substituted C 3 -C 30  hetero aromatic group, 
     optionally, 
     two adjacent R 1 , and/or R 2  and R 3  form an unsubstituted or substituted C 3 -C 30  alicyclic ring, an unsubstituted or substituted C 3 -C 30  hetero alicyclic ring, an unsubstituted or substituted C 6 -C 30  aromatic ring or an unsubstituted or substituted C 3 -C 30  hetero aromatic ring; 
     
       
         
         
             
             
         
       
     
     is an auxiliary ligand; 
     m is an integer of 1 to 3; and 
     n is an integer of 0 to 2; and 
     m+n is an oxidation number of M. 
     As used herein, the term “unsubstituted” means that the specified group bears no substituents, and hydrogen is linked. In this case, hydrogen comprises protium, deuterium and tritium without specific disclosure. 
     As used herein, substituent in the term “substituted” comprises, but is not limited to, unsubstituted or halogen-substituted C1-C20 alkyl, unsubstituted or halogen-substituted C1-C20 alkoxy, halogen, cyano, —CF3, a hydroxyl group, a carboxylic group, a carbonyl group, an amino group, a C1-C10 alkyl amino group, a C6-C30 aryl amino group, a C3-C30 hetero aryl amino group, a C6-C30 aryl group, a C3-C30 hetero aryl group, a nitro group, a hydrazyl group, a sulfonate group, a C1-C20 alkyl silyl group, a C1-C20 alkoxy silyl group, a C3-C20 cycloalkyl silyl group, a C6-C30 aryl silyl group and a C3-C30 hetero aryl silyl group. 
     As used herein, the term “alkyl” refers to a branched or unbranched saturated hydrocarbon group of 1 to 20 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, and the like. 
     As used herein, the term “alkenyl” is a hydrocarbon group of 2 to 20 carbon atoms containing at least one carbon-carbon double bond. The alkenyl group can be substituted with one or more substituents. 
     As used herein, the term “alicyclic” or “cycloalkyl” refers to non-aromatic carbon-containing ring composed of at least three carbon atoms. Examples of alicyclic groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, and the like. The alicyclic group can be substituted with one or more substituents. 
     As used herein, the term “alkoxy” refers to a branched or unbranched alkyl bonded through an ether linkage represented by the formula —O(-alkyl) where alkyl is defined herein. Examples of alkoxy include methoxy, ethoxy, n-propoxy, isopropoxy, butoxy, and tert-butoxy, and the like. 
     As used herein, the term “alkyl amino” refers to a group represented by the formula —NH(-alkyl) or —N(-alkyl) 2  where alkyl is defined herein. Examples of alkyl amino represented by the formula —NH(-alkyl) include, but not limited to, methylamino group, ethylamino group, propylamino group, isopropylamino group, butylamino group, isobutylamino group, (sec-butyl)amino group, (tert-butyl)amino group, pentylamino group, isopentylamino group, (tert-pentyl)amino group, hexylamino group, and the like. Examples of alkyl amino represented by the formula —N(-alkyl) 2  include, but not limited to, dimethylamino group, diethylamino group, dipropylamino group, diisopropylamino group, dibutylamino group, diisobutylamino group, di(sec-butyl)amino group, di(tert-butyl)amino group, dipentylamino group, diisopentylamino group, di(tert-pentyl)amino group, dihexylamino group, N-ethyl-N-methylamino group, N-methyl-N-propylamino group, N ethyl-N-propylamino group and the like. 
     As used herein, the term “aromatic” or “aryl” is well known in the art. The term includes monocyclic rings linked covalently or fused-ring polycyclic groups. An aromatic group can be unsubstituted or substituted. Examples of aromatic or aryl include phenyl, 1-naphthyl, 2-naphthyl, 4-biphenyl, anthracenyl, and phenanthracenyl and the like. Substituents for each of the above noted aryl ring systems are acceptable substituents are defined herein. 
     As used herein, the term “alkyl silyl group” refers to any linear or branched, saturated or unsaturated acyclic or acyclic alkyl, and the alkyl has 1 to 20 carbon atoms. Examples of the alkyl silyl group include a trimethylsilyl group, a trimethylsilyl group, a t-butyldimethylsilyl group, a vinyldimethylsilyl group, a propyldimethylsilyl group, a triphenylsilyl group, a diphenylsilyl group, and a phenylsilyl group. 
     As used herein, the term “halogen” refers to fluorine, chlorine, bromine or iodine atom. 
     As used herein, the term “hetero” in such as “a hetero aromatic ring”, “a hetero cycloalkylene group”, “a hetero arylene group”, “a hetero aryl alkylene group”, “a hetero aryl oxylene group”, “a hetero cycloalkyl group”, “a hetero aryl group”, “a hetero aryl alkyl group”, “a hetero aryloxyl group”, “a hetero aryl amino group” and “a hetero aryl silyl group” means that at least one carbon atom, for example 1-5 carbons atoms, constituting an aromatic ring or an alicyclic ring is substituted with at least one hetero atom selected from the group consisting of N, O, S, Si, Se, P, B and combination thereof. 
     As used herein, the term “hetero aromatic” or “hetero aryl” refers to a heterocycle including hetero atoms selected from N, O and S in a ring where the ring system is an aromatic ring. The term includes monocyclic rings linked covalently or fused-ring polycyclic groups. A hetero aromatic group can be unsubstituted or substituted. Examples of hetero aromatic or hetero aryl include pyridyl, pyrrolyl, pyrazinyl, pyrimidinyl, thienyl (alternatively referred to as thiophenyl), thiazolyl, furanyl, imidazolyl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, oxadiazolyl, and thiadiazolyl. 
     As used herein, the term “hetero aryl oxy” refers to a group represented by the formula —O-(hetero aryl) where hetero aryl is defined herein. 
     For example, when each of R and R 1  to R 3  in Formula 1-1 is independently a C 6 -C 30  aromatic group, each of R and R 1  to R 3  can be independently selected from the group consisting of, but is not limited to, a C 6 -C 30  aryl group, a C 7 -C 30  aryl alkyl group, a C 6 -C 30  aryl oxy group and a C 6 -C 30  aryl amino group. As an example, when each of R and R 1  to R 3  is independently a C 6 -C 30  aryl group, each of R and R 1  to R 3  can be independently selected from the group consisting of, but is not limited to, an unfused or fused aryl group such as phenyl, biphenyl, terphenyl, naphthyl, anthracenyl, pentalenyl, indenyl, indeno-indenyl, heptalenyl, biphenylenyl, indacenyl, phenalenyl, phenanthrenyl, benzo-phenanthrenyl, dibenzo-phenanthrenyl, azulenyl, pyrenyl, fluoranthenyl, triphenylenyl, chrysenyl, tetraphenylenyl, tetracenyl, pleiadenyl, picenyl, pentaphenylenyl, pentacenyl, fluorenyl, indeno-fluorenyl and spiro-fluorenyl. 
     Alternatively, when each of R and R 1  to R 3  in Formula 1 is independently a C 3 -C 30  hetero aromatic group, each of R and R 1  to R 3  can be independently selected from the group consisting of, but is not limited to, a C 3 -C 30  hetero aryl group, a C 4 -C 30  hetero aryl alkyl group, a C 3 -C 30  hetero aryl oxy group and a C 3 -C 30  hetero aryl amino group. As an example, when each of R and R 1  to R 3  is independently a C 3 -C 30  hetero aryl group, each of R and R 1  to R 3  can be independently selected from the group consisting of, but is not limited to, an unfused or fused hetero aryl group such as pyrrolyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridazinyl, triazinyl, tetrazinyl, imidazolyl, pyrazolyl, indolyl, iso-indolyl, indazolyl, indolizinyl, pyrrolizinyl, carbazolyl, benzo-carbazolyl, dibenzo-carbazolyl, indolo-carbazolyl, indeno-carbazolyl, benzo-furo-carbazolyl, benzo-thieno-carbazolyl, carbolinyl, quinolinyl, iso-quinolinyl, phthlazinyl, quinoxalinyl, cinnolinyl, quinazolinyl, quinolizinyl, purinyl, benzo-quinolinyl, benzo-iso-quinolinyl, benzo-quinazolinyl, benzo-quinoxalinyl, acridinyl, phenazinyl, phenoxazinyl, phenothiazinyl, phenanthrolinyl, perimidinyl, phenanthridinyl, pteridinyl, naphthyridinyl, furanyl, pyranyl, oxazinyl, oxazolyl, oxadiazolyl, triazolyl, dioxinyl, benzo-furanyl, dibenzo-furanyl, thiopyranyl, xanthenyl, chromenyl, iso-chromenyl, thioazinyl, thiophenyl, benzo-thiophenyl, dibenzo-thiophenyl, difuro-pyrazinyl, benzofuro-dibenzo-furanyl, benzothieno-benzo-thiophenyl, benzothieno-dibenzo-thiophenyl, benzothieno-benzo-furanyl, benzothieno-dibenzo-furanyl, xanthene-linked Spiro acridinyl, dihydroacridinyl substituted with at least one C 1 -C 10  alkyl and N-substituted spiro fluorenyl. 
     As an example, each of the aromatic group or the hetero aromatic group of R and R 1  to R 3  can consist of one to three aromatic or hetero aromatic rings. When the number of the aromatic or hetero aromatic rings of R and R 1  to R 3  is more than three, conjugated structure in the first compound  232  becomes too long, thus, the first compound  232  can have too narrow energy bandgap. For example, each of the aryl group or the hetero aryl group of R and R 1  to R 3  can be independently selected from the group consisting of, but is not limited to, phenyl, biphenyl, naphthyl, anthracenyl, pyrrolyl, triazinyl, imidazolyl, pyrazolyl, pyridinyl, pyrazinyl, pyrimidinyl, pyridazinyl, furanyl, benzo-furanyl, dibenzo-furanyl, thiophenyl, benzo-thiophenyl, dibenzo-thiophenyl, carbazolyl, acridinyl, carbolinyl, phenazinyl, phenoxazinyl and phenothiazinyl. 
     Alternatively, two adjacent R 1 , and/or R 2  and R 3  can form an unsubstituted or substituted C 3 -C 30  alicyclic ring (e.g., a C 5 -C 10  alicyclic ring), an unsubstituted or substituted C 3 -C 30  hetero alicyclic ring (e.g., a C 3 -C 10  hetero alicyclic ring), an unsubstituted or substituted C 6 -C 30  aromatic ring (e.g., a C 6 -C 20  aromatic ring) or an unsubstituted or substituted C 3 -C 30  hetero aromatic ring (e.g., a C 3 -C 20  hetero aromatic ring). The alicyclic ring, the hetero alicyclic ring, the aromatic ring and the hetero aromatic ring formed by: two adjacent R 1 ; or R 2  and R 3 , are not limited to specific rings. For example, the aromatic ring or the hetero aromatic ring formed by those groups can be independently selected from the group consisting of, but is not limited to, a benzene ring, a pyridine ring, an indole ring, a pyran ring, a fluorene ring unsubstituted or substituted with at least one C 1 -C 10  alkyl group. 
     The first compound  232  being the organometallic compound having the structure of Formula 1-1 has a ligand with fused with multiple aromatic and/or hetero aromatic rings, thus it has narrow full-width at half maximum (FWHM) in photoluminescence spectrum. Particularly, since the first compound  232  has a rigid chemical conformation, its conformation is not rotated in the luminous process so that it can maintain good luminous lifespan. In addition, since the first compound  232  has specific ranges of photoluminescence emissions, the color purity of the light emitted from the first compound  232  can be improved. 
     In addition, the first compound  232  can be a heteroleptic metal complex including two different bidentate ligands coordinated to the central metal atom. (n is a positive integer in Formula 1-1) The photoluminescence color purity and emission colors of the first compound  232  can be controlled with ease by combining two different bidentate ligands. Moreover, it is possible to control the color purity and emission peaks of the first compound  232  by introducing various substituents to each of the ligands. For example, the first compound  232  having the structure of Formula 1-1 can emit yellow to red colors and can improve luminous efficiency of an organic light emitting diode. 
     In one exemplary aspect, the first compound  232  can have the ring (a) with X 3 -X 5 , Y 1  and A to be represented by Formula 1-2. 
     
       
         
         
             
             
         
       
     
     wherein each of X 21  to X 27  is independently CR 1  or N; Y 3  is BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te, TeO 2 , or NR a ; and each of M, R, 
     
       
         
         
             
             
         
       
     
     m, n, to R 3  and R a  is same as defined in Formula 1-1. 
     In an alternative aspect, the first compound  232  can have the ring (b) with X 8 -X 11 , Y 2  and B to be represented by Formula 1-3 
     
       
         
         
             
             
         
       
     
     wherein each of X 31  to X 38  is independently CR 1  or N; Y 4  is BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te, TeO 2 , or NR a ; each of M, 
     
       
         
         
             
             
         
       
     
     m, n, R 1  to R 3  and R a  is same as defined in Formula 1-1. 
     For example, M can be iridium (Ir), palladium (Pd) or platinum (Pt). X 31  to X 38  can be CR 1 . R 1  can be selected from the group consisting of hydrogen, protium, deuterium and a C 1 -C 20  alkyl group unsubstituted or substituted with deuterium, or optionally, two of les of X 31  to X 33  can form a C 6 -C 30  aromatic ring unsubstituted or substituted with a C 1 -C 20  alkyl group. Y 4  can be CR 2 R 3 , N a  or O. Each of R 2  and R 3  can be independently selected from the group consisting of hydrogen, protium, deuterium, a C 1 -C 20  alkyl group unsubstituted or substituted with deuterium and a C 6 -C 30  aromatic group (aryl group). In addition, one of m and n can be 1, and the other one of m and n can be 2. 
     More particularly, in Formula 1-2, X 25  and X 26  are connected to each other to form an aromatic ring or a hetero aromatic ring so that the first compound  232  can be represented by Formula 1-4. Alternatively, in Formula 1-2, X 26  and X 27  are connected to each other to form an aromatic ring or a hetero aromatic ring so that the first compound  232  can be represented by Formula 1-5. 
     
       
         
         
             
             
         
       
     
     wherein each of X 41  to X 45  is independently CR 1  or N; each of M, R, 
     
       
         
         
             
             
         
       
     
     m, n and R 1  to R 3  is same as defined in Formula 1-1; and X 21  to X 24  and Y 3  is same as defined in Formula 1-2; 
     Alternatively, in Formula 1-3, X 31  and X 3  are connected to each other to form an aromatic ring or a hetero aromatic ring so that the first compound  232  can be represented by Formula 1-6. Alternatively, in Formula 1-3, X 32  and X 33  are connected to each other to form an aromatic ring or a hetero aromatic ring so that the first compound  232  can be represented by Formula 1-7. 
     
       
         
         
             
             
         
       
     
     wherein each of X 51  to X 55  is independently CR 1  or N; M, 
     
       
         
         
             
             
         
       
     
     m, n, R 1  to R 3  is same as defined in Formula 1-1; and each of X 34  to X 38  and Y 4  is same as defined in Formula 1-3. 
     For example, M can be iridium (Ir), palladium (Pd) or platinum (Pt). One of X 34  to X 38  and X 51  to X 55  can be N, and the rest of X 34  to X 38  and X 51  to X 55  can be CR 1 . Y 4  can be CR 2 R 3 , N a , O or S. R 1  can be selected from the group consisting of hydrogen, protium, deuterium, a C 1 -C 20  alkyl group unsubstituted or substituted with deuterium, a C 1 -C 20  alkyl silyl group, a C 6 -C 30  aromatic group (aryl group) or a C 3 -C 30  hetero aromatic group (hetero aryl group). Each of R 2  and R 3  can be independently selected from the group consisting of hydrogen, protium, deuterium, a C 1 -C 20  alkyl group unsubstituted or substituted with deuterium, a C 3 -C 30  alicyclic group, a C 3 -C 30  hetero alicyclic group, a C 6 -C 30  aromatic group (aryl group) or a C 3 -C 30  hetero aromatic group (hetero aryl group), or optionally, two adjacent R 1 , and/or R 2  and R 1  can form a C 3 -C 30  alicyclic ring, a C 3 -C 30  hetero alicyclic ring, a C 6 -C 30  aromatic ring or a C 3 -C 30  hetero aromatic ring. 
     For example, in Formula 1-1, the auxiliary ligand 
     
       
         
         
             
             
         
       
     
     can be a bidentate ligand wherein Z 1  and Z 2  are independently selected from the group consisting of an oxygen atom, a nitrogen atom, and a phosphorus atom. The bidentate ligand can be acetylacetonate-containing ligand, or N,N′- or N,O-bidentate anionic ligand. 
     As an example, the center coordination metal can be iridium and the auxiliary ligand 
     
       
         
         
             
             
         
       
     
     can be an acetylacetonate-containing ligand. Namely, the first compound  232  can be represented by one of Formulas 1-8 to 1-11: 
     
       
         
         
             
             
         
       
     
     wherein R in Formulas 1-8 and 1-9 is same as defined in Formula 1-1; each of X 21  to X 24 , X 34  to X 38 , X 41  to X 45  and X 51  to X 55  is independently CR 1  or N; each of Y 3  and Y 4  is independently BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te or TeO 2 , or NR a ; each of R 1  to R 3  and R a  is same as defined in Formula 1-1; each of R 11  to R 13  is independently selected from the group consisting of hydrogen, protium, deuterium, tritium, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrozone group, an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 2 -C 20  alkenyl group, an unsubstituted or substituted C 2 -C 20  alkynyl group, an unsubstituted or substituted C 1 -C 20  alkoxy group, an amino group, an unsubstituted or substituted C 1 -C 20  alkyl amino group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, a carboxyl group, a nitrile group, an isonitrile group, a sulfanyl group, a phosphino group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group and an unsubstituted or substituted C 3 -C 30  hetero aromatic group; m is an integer of 1 to 3; n is an integer of 0 to 2; and wherein m+n is 3. 
     In Formula 1-1, M can be iridium, one of Z 1  and Z 2  can be an oxygen atom, and the other one of Z 1  and Z 2  can be a nitrogen atom. Namely, the first compound  232  can be represented by one of Formulas 1-12 to 1-15. 
     
       
         
         
             
             
         
       
     
     wherein R in Formulas 1-12 and 1-13 is same as defined in Formula 1-1; each of X 21  to X 24 , X 34  to X 38 , X 41  to X 45  and X 51  to X 55  is independently CR 1  or N; each of Y 3  and Y 4  is independently BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te or TeO 2 , or NR a ; each of R 1  to R 3  and R a  is same as defined in Formula 1-1; each of R 61  to R 64  is independently selected from the group consisting of hydrogen, protium, deuterium, tritium, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrozone group, an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 2 -C 20  alkenyl group, an unsubstituted or substituted C 2 -C 20  alkynyl group, an unsubstituted or substituted C 1 -C 20  alkoxy group, an amino group, an unsubstituted or substituted C 1 -C 20  alkyl amino group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, a carboxyl group, a nitrile group, an isonitrile group, a sulfanyl group, a phosphino group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group and an unsubstituted or substituted C 3 -C 30  hetero aromatic group; m is an integer of 1 to 3; n is an integer of 0 to 2; and wherein m+n is 3. 
     In Formula 1-1, M can be iridium, Z 1  and Z 2  can be a nitrogen atom. Namely, the first compound  232  can be represented by one of Formulas 1-16 to 1-23. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein R in Formulas 1-16, 1-17, 1-20 and 1-21 is same as defined in Formula 1-1; each of X 21  to X 24 , X 34  to X 38 , X 41  to X 45  and X 51  to X 55  is independently CR 1  or N; each of Y 3  and Y 4  is independently BR 2 , CR 2 R 3 , C═O, SiR 2 R 3 , GeR 2 R 3 , PR 2 , P═O, O, S, SO 2 , Se, SeO 2 , Te or TeO 2 , or NR a ; each of R 1  to R 3  and R a  is same as defined in Formula 1-1; m is an integer of 1 to 3, n is an integer of 0 to 2, and wherein m+n is 3; each of R 71  to R 73  in Formulas 1-16 to 1-19 is independently selected from the group consisting of hydrogen, protium, deuterium, tritium, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrozone group, an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 2 -C 20  alkenyl group, an unsubstituted or substituted C 2 -C 20  alkynyl group, an unsubstituted or substituted C 1 -C 20  alkoxy group, an amino group, an unsubstituted or substituted C 1 -C 20  alkyl amino group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, a carboxyl group, a nitrile group, an isonitrile group, a sulfanyl group, a phosphino group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group and an unsubstituted or substituted C 3 -C 30  hetero aromatic group; each of R 81  to R 85  in Formulas 1-20 to 1-23 is independently selected from the group consisting of hydrogen, protium, deuterium, tritium, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrozone group, an unsubstituted or substituted C 1 -C 20  alkyl group, an unsubstituted or substituted C 2 -C 20  alkenyl group, an unsubstituted or substituted C 2 -C 20  alkynyl group, an unsubstituted or substituted C 1 -C 20  alkoxy group, an amino group, an unsubstituted or substituted C 1 -C 20  alkyl amino group, an unsubstituted or substituted C 1 -C 20  alkyl silyl group, a carboxyl group, a nitrile group, an isonitrile group, a sulfanyl group, a phosphino group, an unsubstituted or substituted C 3 -C 30  alicyclic group, an unsubstituted or substituted C 3 -C 30  hetero alicyclic group, an unsubstituted or substituted C 6 -C 30  aromatic group and an unsubstituted or substituted C 3 -C 30  hetero aromatic group. 
     For example, the first compound  232  represented by Formula 1-8 can be one of the compounds in Formula 1-24. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     For example, the first compound  232  represented by Formula 1-9 can be one of the compounds in Formula 1-25. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     For example, the first compound  232  represented by Formula 1-10 can be one of the compounds in Formula 1-26. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     When Y4 in Formula 1-11 is an unsubstituted or substituted carbon atom, i.e., CH 2  or CR 2 R 3 , the first compound  232  can be one of the compounds in Formula 1-27. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     When Y4 in Formula 1-11 is an unsubstituted or substituted hetero atom, i.e., NR a  or O, the first compound  232  can be one of the compounds in Formula 1-28. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     For example, the first compound  232  can be one of the compounds in Formula 1-29. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Synthesis Example 1: Synthesis of Compound 369 (Compound RD7 in Formula 8) 
     (1) Synthesis of Compound B-1 
     
       
         
         
             
             
         
       
     
     Compound A-1 (5-bromoquinoline, 50.0 g, 240.33 mmol), propan-2-ylboronic acid (42.25 g, 480.65 mmol), Pd 2 (dba) 3  (tris(dibenzylideneacetone)dipalladium (0), 6.6 g, 3 mol %), SPhos (2-dicyclichexhylphosphino-2′,6′-dimethoxybiphenyl, 9.9 g, 24.03 mmol), potassium phosphate monohydrate (276.71 g, 1.2 mol) and toluene (1000 mL) were put into a reaction vessel, and then the solution was stirred at 120° C. for 12 hours. After the reaction was complete, the solution was cooled down to a room temperature and the solution was extracted with ethyl acetate to remove the solvent. A crude product was purified with column chromatography (eluent: ethyl acetate and hexane) to give the compound B-1 (5-isopropylquinoline, 35.4 g, yield: 86%). 
     MS (m/z): 171.10 
     (2) Synthesis of Compound C-1 
     
       
         
         
             
             
         
       
     
     The compound B-1 (5-isopropylquinoline, 35.4 g, 206.73 mmol), mCBPA (3-chloroperbenzoic acid, 53.5 g, 310.09 mmol) and dichloromethane (500 mL) were put into a reaction vessel, and then the solution was stirred at room temperature for 3 hours. Sodium sulfite (80 g) was added into the solution, the organic layer was washed with water and then placed under reduced pressure to give the compound C-1 (27.5 g, yield: 71%). 
     MS (m/z): 187.10 
     (3) Synthesis of Compound D1 
     
       
         
         
             
             
         
       
     
     The compound C-1 (27.5 g, 146.87 mmol) dissolved in toluene (500 mL) was put into a reaction vessel, phosphoryl trichloride (POCl 3 , 45.0 g, 293.74 mmol) and diisopropylethylamine (DIPEA, 38.0 g, 293.74 mmol) were added into the vessel, and then the solution was stirred at 120° C. for 4 hours. The reactants ware placed under reduced pressure to remove the solvent and extracted with dichloromethane, and then the organic layer was washed with water. Water was removed with MgSO 4 , the crude product was filtered and then the solvent was removed. The crude product was purified with column chromatography to give the compound D-1 (2-chloro-5-isopropylquinoline, 11.8 g, yield: 39%). 
     MS (m/z); 205.07 
     (4) Synthesis of Compound F-1 
     
       
         
         
             
             
         
       
     
     The compound E-1 (1-naphthoic acid, 50 g, 290.30 mmol) and SOCl 2  (200 mL) were put into a reaction vessel, the solution was refluxed for 4 hours, SOCl 2  was removed, ethanol (200 mL) was added, and then the solution was stirred at 70° C. for 7 hours. Water was added, the organic layer was extracted with ether, water was removed with MgSO 4  and then the solution was filtered. The solution was placed under reduced pressure to remove the solvent and to give the compound F-1 (ethyl-1-naphthoate, 53.2 g, yield: 90%). 
     MS (m/z): 200.08 
     (5) Synthesis of Compound G-1 
     
       
         
         
             
             
         
       
     
     The compound F-1 (ethyl-1-naphthoate, 52.3 g, 261.20 mmol), NBS (N-bromosuccinimide, 51.14 g, 287.32 mmol), Pd(OAc) 2  (palladium(II)acetate, 0.6 g, 2.61 mmol), Na 2 S 2 O 8  (124.4 g, 522.40 mmol) and dichloromethane (500 mL) were put into a reaction vessel, TfOH (Trifluoromethanesulfonic acid, 19.6 g, 130.60 mmol) was added into the reaction vessel, and then the solution was stirred at 70° C. for 1 hour. The reactants were cooled to room temperature, the reaction was complete using NaHCO 3 , and then was extracted with dichloromethane. Water in the organic layer was removed with MgSO 4 , the solvent was removed, and then the crude product was purified with column chromatography (eluent: petroleum ether and ethyl acetate) to give the compound G-1 (ethyl-8-bromonaphthalene-1-carboxylate, 54.0 g, yield: 74%). 
     MS (m/z): 277.99 
     (6) Synthesis of Compound H-1 
     
       
         
         
             
             
         
       
     
     The compound G-1 (ethyl-8-bromonaphthalene-1-carboxylate, 54.0 g, 193.46 mmol), bis(pinacolato)diboron (58.6 g, 232.15 mmol), Pd(dppf)Cl 2  ([1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II), 7.1 g, 9.67 mmol), KOAc (potassium acetate, 57.0 g, 580.37 mmol) and 1,4-dioxane (500 mL) were put into a reaction vessel, and then the solution was stirred at 100° C. for 4 hours. The reactants were cooled to room temperature, extracted with ethyl acetate, then water in the organic layer was removed with MgSO 4 , and then the solution was filtered and placed under reduced pressure to remove the solvent. The crude product was purified with column chromatography (eluent: hexane and ethyl acetate) to give the compound H-1 (ethyl8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate, 54.3 g, yield: 86%). 
     MS (m/z): 326.17 
     (7) Synthesis of Compound I-1 
     
       
         
         
             
             
         
       
     
     The compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol), the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene caroboylate, 17.45 g, 53.48 mmol), Pd(OAc) 2  (0.5 g, 2.43 mmol), PPh 3  (chloro(tripphenylphosphine)[2-(2′-amino-1,1′-biphenyl)]palladium(II), 2.6 g, 9.72 mmol), K 2 CO 3  (20.2 g, 145.86 mmol), 1,4-dioxane (100 mL) and water (100 mL) were put into a reaction vessel, and then the solution was stirred at 100° C. for 12 hours. The reactants ware cooled to room temperature and extracted with ethyl acetate, water in the organic layer was removed with MgSO 4 , and then the solution was filtered and placed under reduced pressure to remove the solvent. The crude product was purified with column chromatography (eluent: hexane and ethyl acetate) to give the compound I-1 (ethyl 8-(5-isopropylquinolin-2-yl)naphthalene-1-carboxylate, 13.5 g, yield: 75%). 
     MS (m/z): 369.17 
     (8) Synthesis of Compound J-1 
     
       
         
         
             
             
         
       
     
     The compound I-1 (ethyl 8-(5-isopropylquinolin-2-yl)naphthalene-1-carboxylate, 13.5 g, 36.6 mmol) and THF (100 mL) were put into a reaction vessel and then CH 3 MgBr (21.8 g, 182.70 mmol) was added dropwise into the reaction vessel at 0° C. The solution was raised to room temperature, the reaction was complete after 12 hours, was extracted with ethyl acetate, water in the organic layer was removed with MgSO 4 , and then the solution was filtered and placed under reduced pressure to remove the solvent. The crude product was purified with column chromatography (eluent: hexane and ethyl acetate) to give the compound J-1 (2-(1-(5-isopropylquinolin-2-yl)naphthalene-8-yl)propan-2-ol, 6.9 g, yield: 53%). 
     MS (m/z): 355.19 
     (9) Synthesis of Compound K-1 
     
       
         
         
             
             
         
       
     
     The compound J-1 (2-(1-(5-isopropylquinolin-2-yl)naphthalene-8-yl)propan-2-ol, 20 g, 56.26 mmol) and a mixed aqueous solution (200 mL) of acetic acid and sulfuric acid were put into a reaction vessel, and then the solution was refluxed for 16 hours. After the reaction was complete, the solution was cooled to room temperature, and then the reactants were added dropwise into sodium hydroxide aqueous solution with ice. The organic layer was extracted with dichloromethane and water was removed with MgSO 4 . The solvent was removed and then the crude product was recrystallized with toluene and ethanol to give the compound K-1 (9-isopropyl-7,7-dimethyl-7H-naphtho[1,8-bc]acridine, 10.25 g, yield: 54%) of yellow solid. 
     MS (m/z): 337.18 
     (10) Synthesis of Compound L-1 
     
       
         
         
             
             
         
       
     
     The compound K-1 (10.25 g, 30.37 mmol), 2-ethoxyethanol (200 mL) and distilled water (50 mL) were put into a reaction vessel, the solution was bubbled with nitrogen for 1 hour, IrCl 3 .H 2 O (4.4 g, 13.81 mmol) was added into the reaction vessel, and then the solution was refluxed for 2 days. After the reaction was complete, the solution was cooled to room temperature, and then the obtained solid was filtered. The solid was washed with hexane and water and dried to give the compound L-1 (4.0 g, yield: 32%). 
     (11) Synthesis of Compound 369 
     
       
         
         
             
             
         
       
     
     The compound L-1 (4.0 g, 2.21 mmol), 3,7-diethylnonane-4,6-dione (4.7 g, 22.09 mmol), Na 2 CO 3  (4.7 g, 441.8 mmol) and 2-ethoxyethanol (100 mL) were put into a reaction vessel, and then the solution was stirred slowly for 24 hours. After the reaction was complete, dichloromethane was added into the reactants to dissolve product, and then the solution was filtered with celite. The solvent was removed, the solid was filtered using filter paper, then the filtered solid was put into isopropanol, and then the solution was stirred. The solution was filtered to remove isopropanol, and the solution was dried and recrystallized with dichloromethane and isopropanol. High purity of compound 369 (2.5 g, yield: 53%) was obtained using a sublimation purification instrument. 
     MS (m/z): 1076.48 
     Synthesis Example 2: Synthesis of compound 2 (compound RD5 in Formula 8) 
     (1) Synthesis of Compound C-2 
     
       
         
         
             
             
         
       
     
     The compound C-2 (ethyl 3-6-(isopropylisoqunolin-1-yl)-naphthoate (14.4 g, yield: 80%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-2 (1-chloro-6-isopropylisoquinoline, 10 g, 48.62 mmol) and compound B-2 (ethyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)-2-naphthoate (17.45 g, 53.50 mmol) were used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan yl)naphthalene-1-carboxylate, respectively. 
     MS (m/z): 369.17 
     (2) Synthesis of Compound D-2 
     
       
         
         
             
             
         
       
     
     The compound D-2 (2-(3-(6-isopropylisoquinolin-1-yl)naphthalen-2-yl)propan-2-ol, 6.9 g, yield: 50%) was obtained by repeating the synthesis process of the compound J-1 except that the compound C-2 (ethyl 3-(6-isopropylisoquinolin-1-yl)-2-naphthoate, 14.4 g, 39.0 mmol) was used instead of the compound I-1 (ethyl 8-(5-isopropylquinolin-2-yl)naphthalene-1-carboxylate, 13.5 g, 36.5 mmol). 
     MS (m/z): 355.19 
     (3) Synthesis of Compound E-2 
     
       
         
         
             
             
         
       
     
     The compound E-2 (5-isopropyl-7,7-dimethyl-7H-benzo[de]naphtha[2,3-h]quinolone, 11.39 g, yield: 60%) was obtained by repeating the synthesis process of the Compound K-1 except that the compound D-2 (2-(3-(6-isopropylisoquinolin-1-yl)naphthalen-2-yl)propan-2-ol, 20 g, 56.26 mmol) was used instead of the compound J-1 (2-(1-(5-isopropylquinolin-2-yl)naphthalene-8-yl)propan-2-ol, 20 g, 56.26 mmol). 
     MS (m/z): 337.18 
     (4) Synthesis of Compound F-2 
     
       
         
         
             
             
         
       
     
     The compound F-2 (4.7 g, yield: 34%) was obtained by repeating the synthesis process of the Compound L-1 except that the compound E-2 (11.39 g, 33.76 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (5) Synthesis of Compound 2 
     
       
         
         
             
             
         
       
     
     The compound 2 (3.2 g, yield: 57%) was obtained by repeating the synthesis process of compound 369 except that the Compound F-2 (4.7 g, 2.61 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1076.48 
     Synthesis Example 3: Synthesis of Compound 501 (Compound RD8 in Formula 8) 
     (1) Synthesis of Compound C-3 
     
       
         
         
             
             
         
       
     
     The compound C-3 (ethyl 8-6-(isopropylisoquinolin-3-yl)-naphthoate, 12.6 g, yield: 70%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-3 (3-chloro-6-isopropylisoquinoline, 10 g, 48.62 mmol) was used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol). 
     MS (m/z): 369.17 
     (2) Synthesis of Compound D-3 
     
       
         
         
             
             
         
       
     
     The compound D-3 (2-(8-(6-isopropylisoquinolin-3-yl)naphthalen-1-yl)propan-2-ol, 7.3 g, yield: 60%) was obtained by repeating the synthesis process of the Compound J-1 except that the compound C-3 (ethyl 8-(6-isopropylisoquinolin-3-yl)naphthoate, 12.6 g, 34.0 mmol) was used instead of the compound I-1 (ethyl 8-(5-isopropylquinolin-2-yl)naphthalene-1-carboxylate, 13.5 g, 36.5 mmol). 
     MS (m/z): 355.19 
     (3) Synthesis of Compound E-3 
     
       
         
         
             
             
         
       
     
     The compound E-3 (2-isopropyl-13,13-dimethyl-13H-naphtho[1,8-bc]phenanthridine, 4.3 g, yield: 62%) was obtained by repeating the synthesis process of the Compound K-1 except that the compound D-3 (2-(8-(6-isopropylisoquinolin-3-yl)naphthalen-1-yl)propan-2-ol, 7.3 g, 20.4 mmol) was used instead of the compound J-1 (2-(1-(5-isopropylquinolin-2-yl)naphthalene-8-yl)propan-2-ol, 20 g, 56.26 mmol). 
     MS (m/z): 337.18 
     (4) Synthesis of Compound F-3 
     
       
         
         
             
             
         
       
     
     The compound F-3 (1.9 g, yield: 37%) was obtained by repeating the synthesis process of the compound L-1 except that the compound E-3 (2-isopropyl-13,13-dimethyl-13H-naphtho[1,8-bc]phenanthridine, 4.3 g, 12.6 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (5) Synthesis of Compound 501 
     
       
         
         
             
             
         
       
     
     The compound 501 (1.4 g, yield: 60%) was obtained by repeating the synthesis process of compound 369 except that the compound F-3 (1.9 g, 1.07 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1076.48 
     Synthesis Example 4: Synthesis of Compound 182 (compound RD6 in Formula 8) 
     (1) Synthesis of Compound C-4 
     
       
         
         
             
             
         
       
     
     The compound C-4 (12.2 g, yield: 68%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-4 (10 g, 48.62 mmol) and the compound B-4 (17.45 g, 53.48 mmol) were used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 369.17 
     (2) Synthesis of Compound D-4 
     
       
         
         
             
             
         
       
     
     The compound D-4 (6.8 g, yield: 58%) was obtained by repeating the synthesis process of the compound J-1 except that the compound C-4 (12.2 g, 33.02 mmol) was used instead of the compound I-1 (ethyl 8-(5-isopropylquinolin-2-yl)naphthalene-1-carboxylate, 13.5 g, 36.5 mmol). 
     MS (m/z): 355.19 
     (3) Synthesis of Compound E-4 
     
       
         
         
             
             
         
       
     
     The compound E-4 (4.1 g, yield: 63%) was obtained by repeating the synthesis process of the compound K-1 except that the compound D-4 (6.8 g, 19.15 mmol) was used instead of the compound J-1 (2-(1-(5-isopropylquinolin-2-yl)naphthalene-8-yl)propan-2-ol, 20 g, 56.26 mmol). 
     MS (m/z): 337.18 
     (4) Synthesis of Compound F-4 
     
       
         
         
             
             
         
       
     
     The compound F-4 (2.1 g, yield: 42%) was obtained by repeating the synthesis process of the compound L-1 except that the compound E-4 (4.1 g, 12.15 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (5) Synthesis of Compound 182 
     
       
         
         
             
             
         
       
     
     The compound 182 (1.1 g, yield: 57%) was obtained by repeating the synthesis process of compound 369 except that the compound F-4 (2.1 g, 1.17 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1076.48 
     Synthesis Example 5: Synthesis of Compound 154 (Compound RD9 in Formula 8) 
     (1) Synthesis of Compound C-5 
     
       
         
         
             
             
         
       
     
     The compound C-5 (11.8 g, yield: 78%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-5 (10 g, 48.62 mmol) and the compound B-5 (14.4 g, 53.48 mmol) were used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 312.16 
     (2) Synthesis of Compound D-5 
     
       
         
         
             
             
         
       
     
     The compound C-5 (11.8 g, 37.75 mmol) and dimethylsulfoxide (DMSO) (200 mL) were put into a reaction vessel, then CuI (10.8 g, 56.66 mmol) was added into the reaction vessel, and then the solution was refluxed at 150° C. for 12 hours. After the reaction was complete, the solution was filtered, extracted with ethyl acetate, water in the organic layer was removed with MgSO 4 , and then the solution was filtered and placed under reduced pressure to remove the solvent. The crude product was purified with column chromatography (eluent: hexane and ethyl acetate) to give the compound D-5 (4.6 g, yield: 39%). 
     MS (m/z): 310.15 
     (3) Synthesis of Compound E-5 
     
       
         
         
             
             
         
       
     
     The compound D-5 (4.6 g, 14.82 mmol), 1-iodobenzene (3.3 g, 16.30 mmol) and toluene (200 mL) were put into a reaction vessel, then Pd 2 (dba) 3  (0.7 g, 0.74 mmol), P(t-Bu) 3  (Tri-tert-butylphosphine, 0.3 g, 1.48 mmol) and NaOt-Bu (sodium tert-butoxide, 2.8 g, 29.64 mmol) were added into the reaction vessel, and then the solution was refluxed at 100° C. for 24 hours. After the reaction was complete, the solution was extracted with ethyl acetate, water in the organic layer was removed with MgSO 4 , and then the solution was filtered and placed under reduced pressure to remove the solvent. The crude product was purified with column chromatography (eluent: hexane and ethyl acetate) to give the compound E-5 (4.6 g, yield: 81%). 
     MS (m/z): 386.18 
     (4) Synthesis of Compound F-5 
     
       
         
         
             
             
         
       
     
     The compound F-5 (2.5 g, yield: 47%) was obtained by repeating the synthesis process of the compound L-1 except that the compound E-5 (4.6 g, 11.90 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (5) Synthesis of Compound 154 
     
       
         
         
             
             
         
       
     
     The compound 154 (1.4 g, yield: 46%) was obtained by repeating the synthesis process of compound 369 except that the compound F-5 (2.5 g, 1.25 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1174.47 
     Synthesis Example 6: Synthesis of Compound 334 (Compound RD10 in Formula 8) 
     (1) Synthesis of Compound C-6 
     
       
         
         
             
             
         
       
     
     The compound C-6 (11.4 g, yield: 75%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-6 (10 g, 48.62 mmol) and the compound B-6 (14.4 g, 53.48 mmol) were used instead of the compound D-1 (2-chloro isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 312.16 
     (2) Synthesis of Compound D-6 
     
       
         
         
             
             
         
       
     
     The compound D-6 (6.8 g, yield: 58%) was obtained by repeating the synthesis process of the compound D5 except that the compound C-6 (11.4 g, 35.49 mmol) was used instead of the compound C-5 (11.8 g, 37.77 mmol). 
     MS (m/z): 310.15 
     (3) Synthesis of Compound E-6 
     
       
         
         
             
             
         
       
     
     The compound E-6 (5.6 g, yield: 78%) was obtained by repeating the synthesis process of the compound E-5 except that the compound D-6 (5.8 g, 18.61 mmol) was used instead of the compound D-5 (4.6 g, 14.82 mmol). 
     MS (m/z): 386.18 
     (4) Synthesis of Compound F-6 
     
       
         
         
             
             
         
       
     
     The compound F-6 (2.8 g, yield: 42%) was obtained by repeating the synthesis process of the compound L-1 except that the compound E-6 (5.6 g, 14.49 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (5) Synthesis of Compound 334 
     
       
         
         
             
             
         
       
     
     The compound 334 (2.0 g, yield: 61%) was obtained by repeating the synthesis process of compound 369 except that the compound F-6 (2.8 g, 1.38 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1174.47 
     Synthesis Example 7: Synthesis of Compound 465 (Compound RD11 in Formula 8) 
     (1) Synthesis of Compound C-7 
     
       
         
         
             
             
         
       
     
     The compound C-7 (9.0 g, yield: 50%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-7 (10 g, 48.62 mmol) and the compound B-7 (14.4 g, 53.48 mmol) were used instead of the compound D-1 (2-chloro isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 312.16 
     (2) Synthesis of Compound D-7 
     
       
         
         
             
             
         
       
     
     The compound D-7 (7.4 g, yield: 55%) was obtained by repeating the synthesis process of the compound D-5 except that the compound C-7 (9.0 g, 28.69 mmol) was used instead of the compound C-5 (11.8 g, 37.77 mmol). 
     MS (m/z): 310.15 
     (3) Synthesis of Compound E-7 
     
       
         
         
             
             
         
       
     
     The compound E-7 (4.7 g, yield: 77%) was obtained by repeating the synthesis process of the compound E-5 except that the compound D-7 (4.9 g, 15.78 mmol) was used instead of the compound D-5 (4.6 g, 14.82 mmol). 
     MS (m/z): 386.18 
     (4) Synthesis of Compound F-7 
     
       
         
         
             
             
         
       
     
     The compound F-7 (2.6 g, yield: 48%) was obtained by repeating the synthesis process of the compound L-1 except that the compound E-7 (4.7 g, 12.16 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (5) Synthesis of Compound 465 
     
       
         
         
             
             
         
       
     
     The compound 465 (2.0 g, yield: 64%) was obtained by repeating the synthesis process of compound 369 except that the compound F-7 (2.6 g, 1.33 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1174.47 
     Synthesis Example 8: Synthesis of Compound 582 (Compound RD12 in Formula 8) 
     (1) Synthesis of Compound C-8 
     
       
         
         
             
             
         
       
     
     The compound C-8 (9.0 g, yield: 50%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-8 (10 g, 48.62 mmol) and the compound B-8 (14.4 g, 53.48 mmol) were used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 312.16 
     (2) Synthesis of Compound D-8 
     
       
         
         
             
             
         
       
     
     The compound D-8 (7.4 g, yield: 55%) was obtained by repeating the synthesis process of the compound D-5 except that the compound C-8 (10.0 g, 35.01 mmol) was used instead of the compound C-5 (11.8 g, 37.77 mmol). 
     MS (m/z): 310.15 
     (3) Synthesis of Compound E-8 
     
       
         
         
             
             
         
       
     
     The compound E-8 (5.3 g, yield: 83%) was obtained by repeating the synthesis process of the compound E-5 except that the compound D-8 (5.1 g, 15.45 mmol) was used instead of the compound D-5 (4.6 g, 14.82 mmol). 
     MS (m/z): 386.18 
     (4) Synthesis of Compound F-8 
     
       
         
         
             
             
         
       
     
     The compound F-8 (2.4 g, yield: 39%) was obtained by repeating the synthesis process of the compound L-1 except that the compound E-8 (5.3 g, 13.66 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (5) Synthesis of Compound 582 
     
       
         
         
             
             
         
       
     
     The compound 582 (1.8 g, yield: 64%) was obtained by repeating the synthesis process of compound 369 except that the compound F-8 (2.4 g, 1.1 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1174.47 
     Synthesis Example 9: Synthesis of Compound 168 (Compound RD13 in Formula 8) 
     (1) Synthesis of Compound C-9 
     
       
         
         
             
             
         
       
     
     The compound C-9 (9.9 g, yield: 67%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-9 (10 g, 44.71 mmol) and the compound B-9 (13.3 g, 49.18 mmol) were used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 331.14 
     (2) Synthesis of Compound D-9 
     
       
         
         
             
             
         
       
     
     The compound C-9 (9.9 g, 29.88 mmol) and DMF (100 mL) were put into a reaction vessel, and the compound C-9 was dissolved in DMF, K 2 CO 3  (12.4 g, 89.62 mmol) was added into the reaction vessel, and then the solution was stirred at 100° C. for 1 hour. After the reaction was complete, the solution was cooled to room temperature and then ethanol (100 mL) was added into the reaction vessel. After the mixture was distilled under reduced pressure, the reactants were recrystallized with chloroform/ethyl acetate to give the compound D-9 (4.9 g, yield: 53%). 
     MS (m/z): 311.13 
     (3) Synthesis of Compound E-9 
     
       
         
         
             
             
         
       
     
     The compound E-9 (3.1 g, yield: 50%) was obtained by repeating the synthesis process of the compound L-1 except that the compound D-9 (4.9 g, 15.83 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (4) Synthesis of Compound 168 
     
       
         
         
             
             
         
       
     
     The compound 168 (2.0 g, yield: 54%) was obtained by repeating the synthesis process of compound 369 except that the compound E-9 (3.1 g, 1.80 mmol) was used instead of the Compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1024.38 
     Synthesis Example 10: Synthesis of Compound 348 (Compound RD14 in Formula 8) 
     (1) Synthesis of Compound C-10 
     
       
         
         
             
             
         
       
     
     The compound C-10 (9.0 g, yield: 64%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-10 (10 g, 44.71 mmol) and the compound B-10 (13.3 g, 49.18 mmol) were used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 331.14 
     (2) Synthesis of Compound D-10 
     
       
         
         
             
             
         
       
     
     The compound D-10 (5.0 g, yield: 55%) was obtained by repeating the synthesis process of the compound D-9 except that the compound C-10 (9.6 g, 29.06 mmol) was used instead of the compound C-9 (9.9 g, 28.88 mmol). 
     MS (m/z): 311.13 
     (3) Synthesis of Compound E-10 
     
       
         
         
             
             
         
       
     
     The compound E-10 (3.5 g, yield: 57%) was obtained by repeating the synthesis process of the compound L-1 except that the compound D-10 (5.0 g, 15.98 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (4) Synthesis of Compound 348 
     
       
         
         
             
             
         
       
     
     The compound 348 (1.8 g, yield: 43%) was obtained by repeating the synthesis process of compound 369 except that the compound E-10 (3.5 g, 2.07 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1024.38 
     Synthesis Example 11: Synthesis of Compound 483 (Compound RD15 in Formula 8) 
     (1) Synthesis of Compound C-11 
     
       
         
         
             
             
         
       
     
     The compound C-11 (7.9 g, yield: 53%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-11 (10 g, 44.71 mmol) and the compound B-11 (13.3 g, 49.18 mmol) were used instead of the Compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 331.14 
     (2) Synthesis of Compound D-11 
     
       
         
         
             
             
         
       
     
     The compound D-11 (3.8 g, yield: 51%) was obtained by repeating the synthesis process of the compound D-9 except that the compound C-11 (7.9 g, 23.07 mmol) was used instead of the compound C-9 (9.9 g, 28.88 mmol). 
     MS (m/z): 311.13 
     (3) Synthesis of Compound E-11 
     
       
         
         
             
             
         
       
     
     The compound E-11 (3.0 g, yield: 63%) was obtained by repeating the synthesis process of the compound L-1 except that the compound D-11 (3.8 g, 12.20 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (4) Synthesis of Compound 483 
     
       
         
         
             
             
         
       
     
     The compound 483 (1.6 g, yield: 44%) was obtained by repeating the synthesis process of compound 369 except that the compound E-11 (3.0 g, 1.75 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1024.38 
     Synthesis Example 12: Synthesis of Compound 598 (Compound RD16 in Formula 8) 
     (1) Synthesis of Compound C-12 
     
       
         
         
             
             
         
       
     
     The compound C-12 (9.8 g, yield: 66%) was obtained by repeating the synthesis process of the compound I-1 except that the compound A-12 (10 g, 44.71 mmol) and the compound B-12 (13.3 g, 49.18 mmol) were used instead of the compound D-1 (2-chloro-5-isopropylquinoline, 10 g, 48.62 mmol) and the compound H-1 (ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxanborolan-2-yl)naphthalene-1-carboxylate (17.45 g, 53.48 mmol), respectively. 
     MS (m/z): 331.14 
     (2) Synthesis of Compound D-12 
     
       
         
         
             
             
         
       
     
     The compound D-12 (5.0 g, yield: 54%) was obtained by repeating the synthesis process of the compound D-9 except that the compound C-12 (9.8 g, 29.51 mmol) was used instead of the compound C-9 (9.9 g, 28.88 mmol). 
     MS (m/z): 311.13 
     (3) Synthesis of Compound E-12 
     
       
         
         
             
             
         
       
     
     The compound E-12 (3.4 g, yield: 55%) was obtained by repeating the synthesis process of the compound L-1 except that the compound D-12 (5.0 g, 15.93 mmol) was used instead of the compound K-1 (10.25 g, 30.37 mmol). 
     (4) Synthesis of Compound 598 
     
       
         
         
             
             
         
       
     
     The compound 598 (1.6 g, yield: 39%) was obtained by repeating the synthesis process of compound 369 except that the compound E-12 (3.4 g, 1.99 mmol) was used instead of the compound L-1 (4.0 g, 2.21 mmol). 
     MS (m/z): 1024.38 
     Synthesis Example 13: Synthesis of Compound RD1 (Compound 4 in Formula 1-24) 
     (1) Synthesis of Compound B-1 
     
       
         
         
             
             
         
       
     
     The compound A-1 (1-chloro-6-isobutylisoquinoline, 10 g, 45.51 mmol), ethyl 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-naphthoate (16.3 g, 50.06 mmol), Pd(OAc) 2  (0.51 g, 2.28 mmol), PPh 3  (2.39 g, 0.91 mmol), K 2 CO 3  (18.9 g, 136.53 mmol), 1-4-dioxane (100 mL) and water (100 mL) were stirred at 100° C. for 12 hours. After cooling to room temperature, extraction was performed with ethyl acetate, and water in the organic layer was removed using MgSO 4 . Then, the mixture was filtered under reduced pressure to remove the solvent. The mixture was wet-purified using hexane and ethyl acetate to obtain the compound B-1 (10 g, 26.07 mmol). (yield: 57%) 
     (2) Synthesis of Compound C-1 
     
       
         
         
             
             
         
       
     
     The compound B-1 (ethyl 3-(6-isobutylisoquinolin-1-yl)-2-naphthoate, 10 g, 26.07 mmol) and THF (100 mL) were added, and CH 3 MgBr (15.5 g, 130 mmol) was slowly added at 0° C. The temperature was raised to room temperature, and the reaction was terminated after 12 hours. The mixture was extracted with ethyl acetate, water in the organic layer was removed using MgSO 4 , and the solvent was removed under reduced pressure. The mixture was wet-purified using hexane and ethyl acetate, and the compound C-1 (7 g, 18.94 mmol) was obtained. (yield: 73%) 
     (3) Synthesis of Compound D-1 
     
       
         
         
             
             
         
       
     
     The compound C-1 (2-(3-(6-isobutylisoquinolin-1-yl)naphthalen-2-yl)propan-2-ol, 10 g, 27.06 mmol) was added to a mixed aqueous solution of acetic acid and sulfuric acid (200 mL), and the mixture was reflux and stirred for 16 hours. After completion of the reaction, the temperature was lowered to room temperature, and the reactant was slowly added to the sodium hydroxide aqueous solution. After extracting the organic layer using dichloromethane and removing water using MgSO 4 , the organic solvent was removed under reduced pressure. The mixture was recrystallized using toluene and ethanol to obtain the compound D-1 (5 g, 14.22 mmol) in a yellow solid state. (yield: 53%) 
     (4) Synthesis of Compound E-1 
     
       
         
         
             
             
         
       
     
     The compound D-1 (5-isobutyl-7,7-dimethyl-7H-benzo[de]naphtho[2,3-h]quinoline, 10 g, 28.45 mmol), 2-ethoxyethanol (200 mL) and distilled water (50 mL) were added, and nitrogen was injected to the mixture for 1 hour. IrCl3.H2O (4.5 g, 12.93 mmol) was put in the reaction vessel and refluxed for 2 days. After completion of the reaction, the temperature was lowered to room temperature and the resulting solid was filtered. After washing the solid with methanol and drying the solid, the compound E-1 (7.0 g, 6.05 mmol) was obtained. (yield: 21%) 
     (5) Synthesis of Compound RD1 
     
       
         
         
             
             
         
       
     
     The compound E-1 (10 g, 8.64 mmol), 3,7-diethylnonane-4,6-dione (18.3 g, 86.4 mmol) and Na 2 CO 3  (18.3 g, 172.8 mmol) were added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol and stirred, and then the filtered solid was dried. Recrystallization and sublimation purification using dichloromethane and isopropanol were performed to obtain the compound RD1 with high purity (5 g, 4.53 mmol). (yield: 52%) 
     Synthesis Example 14: Synthesis of Compound RD2 (Compound 184 in Formula 1-25) 
     (1) Synthesis of Compound B-2 
     
       
         
         
             
             
         
       
     
     The compound A-2 (1-chloro-6-isobutylisoquinoline, 10 g, 45.51 mmol), ethyl 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1-naphthoate (16.3 g, 50.06 mmol), Pd(OAc) 2  (0.51 g, 2.28 mmol), PPh 3  (2.39 g, 0.91 mmol), K 2 CO 3  (18.9 g, 136.53 mmol), 1-4-dioxane (100 mL) and water (100 mL) were stirred at 100° C. for 12 hours. After cooling to room temperature, extraction was performed with ethyl acetate, and water in the organic layer was removed using MgSO 4 . Then, the mixture was filtered under reduced pressure to remove the solvent. The mixture was wet-purified using hexane and ethyl acetate to obtain the compound B-2 (9 g, 23.47 mmol). (yield: 52%) 
     (2) Synthesis of Compound C-2 
     
       
         
         
             
             
         
       
     
     The compound B-2 (ethyl 2-(6-isobutylisoquinolin-1-yl)-1-naphthoate, 10 g, 26.07 mmol) and THF (100 mL) were added, and CH 3 MgBr (15.5 g, 130 mmol) was slowly added at 0° C. The temperature was raised to room temperature, and the reaction was terminated after 12 hours. The mixture was extracted with ethyl acetate, water in the organic layer was removed using MgSO 4 , and the solvent was removed under reduced pressure. The mixture was wet-purified using hexane and ethyl acetate, and the compound C-2 (6 g, 16.23 mmol) was obtained. (yield: 62%) 
     (3) Synthesis of Compound D-2 
     
       
         
         
             
             
         
       
     
     The compound C-2 (2-(2-(6-isobutylisoquinolin-1-yl)naphthalen-1-yl)propan-2-ol, 10 g, 27.06 mmol) was added to a mixed aqueous solution of acetic acid and sulfuric acid (200 mL), and the mixture was reflux and stirred for 16 hours. After completion of the reaction, the temperature was lowered to room temperature, and the reactant was slowly added to the sodium hydroxide aqueous solution. After extracting the organic layer using dichloromethane and removing water using MgSO 4 , the organic solvent was removed under reduced pressure. The mixture was recrystallized using toluene and ethanol to obtain the compound D-2 (4 g, 11.38 mmol) in a yellow solid state. (yield: 42%) 
     (4) Synthesis of Compound E-2 
     
       
         
         
             
             
         
       
     
     The compound D-2 (5-isobutyl-7,7-dimethyl-7H-benzo[de]naphtho[1,2-h]quinoline, 10 g, 28.45 mmol), 2-ethoxyethanol (200 mL) and distilled water (50 mL) were added, and nitrogen was injected to the mixture for 1 hour. IrCl3.H2O (4.5 g, 12.93 mmol) was put in the reaction vessel and refluxed for 2 days. After completion of the reaction, the temperature was lowered to room temperature and the resulting solid was filtered. After washing the solid with methanol and drying the solid, the compound E-2 (10 g, 8.65 mmol) was obtained. (yield: 30%) 
     (5) Synthesis of Compound RD2 
     
       
         
         
             
             
         
       
     
     The compound E-2 (10 g, 8.64 mmol), 3,7-diethylnonane-4,6-dione (18.3 g, 86.4 mmol) and Na 2 CO 3  (18.3 g, 172.8 mmol) were added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol and stirred, and then the filtered solid was dried. The mixture was recrystallized and purified using dichloromethane and isopropanol to obtain the compound RD2 with high purity (4 g, 3.98 mmol). (yield: 46%) 
     Synthesis Example 15: Synthesis of Compound RD3 (Compound 371 in Formula 1-26) 
     (1) Synthesis of Compound B-3 
     
       
         
         
             
             
         
       
     
     The compound A-3 (5-bromoquinoline, 50 g, 240.33 mmol), isobutylboronic acid (49 g, 480.65 mmol), Pd 2 (dba) 3  (6.6 g, 3 mol %), Sphos (2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, 9.9 g, 24.03 mmol), potassium phosphate monohydrate (276.71 g, 1.2 mol) and toluene (1000 mL) were stirred at 120° C. for 12 hours. After completion of the reaction, the temperature was lowered, and the mixture was extracted with ethyl acetate. After the solvent was removed, the mixture was wet-purified using ethyl acetate and hexane to obtain the compound B-3 (35 g, 188.92 mmol). (yield: 79%) 
     (2) Synthesis of Compound C-3 
     
       
         
         
             
             
         
       
     
     The compound B-3 (5-isobutylquinoline, 35 g, 188.92 mmol), 3-chloroperbenzoic acid (57 g, 283.38 mmol) and dichloromethane (500 mL) were stirred at room temperature for 3 hours. After completion of the reaction, sodium sulfite (80 g) was added into the mixture. The organic layer was extracted and the pressure was lowered so that the compound C-3 (27 g, 134.15 mmol) was obtained. (yield: 71%) 
     (3) Synthesis of Compound D-3 
     
       
         
         
             
             
         
       
     
     The compound C-3 (25 g, 124.22 mmol) and toluene (500 mL) were added, and phosphoryl trichloride (38.1 g, 248.44 mmol) and diisopropylethylamine (32.1 g, 248.44 mmol) were added into the mixture. The mixture was stirred at the temperature of 120° C. for 4 hours. After completion of the reaction, the mixture was extracted with dichloromethane, and the pressure was lowered. The mixture was filtered using MgSO 4  under reduced pressure, and the organic solvent was removed. The mixture was wet-purified to obtain the compound D-3 (30 g, 91.0 mmol). (yield: 73%) 
     (4) Synthesis of Compound E-3 
     
       
         
         
             
             
         
       
     
     The compound D-3 (10 g, 45.51 mmol), ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)naphthalene-1-carboxylate (16.33 g, 50.06 mmol), Pd(OAc) 2  (0.5 g, 2.28 mmol), PPh 3  (2.4 g, 9.10 mmol), K 2 CO 3  (18.9 g, 136.53 mmol), 1,4-dioxane (100 mL) and water (100 mL)) were stirred at 100° C. for 12 hours. After completion of the reaction, the mixture was extracted with ethyl acetate, and water in the organic layer was removed using MgSO 4 . The solvent was removed from the mixture by lowering the pressure. The mixture was wet-purified using hexane and ethyl acetate to obtain the compound E-3 (13 g, 33.90 mmol) was obtained. (yield: 74%) 
     (5) Synthesis of Compound F3 
     
       
         
         
             
             
         
       
     
     The compound E-3 (10 g, 26.07 mmol) and THF (100 mL) were added, and CH 3 MgBr (15.5 g, 130.35 mmol) was slowly added at 0° C. After the reaction proceeded at room temperature for 12 hours, the mixture was worked-up using ethyl acetate and MgSO 4 . The mixture was wet-purified using hexane and ethyl acetate to obtain the compound F-3 (6 g, 16.24 mmol). (yield: 62%) 
     (5) Synthesis of Compound G3 
     
       
         
         
             
             
         
       
     
     The compound F-3 (20 g, 54.12 mmol) and a mixed aqueous solution of acetic acid and sulfuric acid (200 mL) were added and refluxed for 16 hours. After completion of the reaction, the reactant was slowly added to a cold aqueous sodium hydroxide (cool sodium hydroxide) solution. After work-up using dichloromethane and MgSO 4 , and the mixture was recrystallized using toluene and ethanol to obtain the compound G-3 (10 g, 28.45 mmol) in a yellow solid state. (yield: 53%) 
     (5) Synthesis of Compound H3 
     
       
         
         
             
             
         
       
     
     The compound G-3 (10 g, 28.45 mmol), 2-ethoxyethanol (200 mL) and distilled water (50 mL) were added, and nitrogen was bubbled for 1 hour. Then, IrCl 3 .H 2 O (4.5 g, 14.22 mmol) was added to the reaction vessel, and the mixture was refluxed for 2 days. After completion of the reaction, the temperature was slowly lowered to room temperature and the resulting solid was filtered. The solid was washed with hexane and methanol and dried to obtain the compound H-3 (6.0 g, 5.19 mmol). (yield: 18%) 
     (5) Synthesis of Compound RD3 
     
       
         
         
             
             
         
       
     
     The compound H-3 (10 g, 8.64 mmol), 3,7-diethylnonane-4,6-dione (18.3 g, 86.4 mmol) and Na 2 CO 3  (18.3 g, 172.8 mmol) was added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol, and the mixture was stirred. After stirring, the mixture was filtered, and the filtered solid was dried. The solid was recrystallized using dichloromethane and isopropanol and was purified to obtain the compound RD3 (4 g, 3.62 mmol) with high purity. (yield: 42%) 
     Synthesis Example 16: Synthesis of Compound RD4 (Compound 503 in Formula 1-27) 
     (1) Synthesis of Compound B-4 
     
       
         
         
             
             
         
       
     
     The compound A-4 (10 g, 45.51 mmol), ethyl 8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)naphthalene-1-carboxylate (16.33 g, 50.06 mmol), Pd(OAc) 2  (0.5 g, 2.28 mmol), PPh 3  (2.4 g, 9.10 mmol), K 2 CO 3  (18.9 g, 136.53 mmol), 1,4-dioxane (100 mL) and water (100 mL) were stirred at 100° C. for 12 hours. After completion of the reaction, the mixture was extracted with ethyl acetate, and water in the organic layer was removed using MgSO 4 . The solvent was removed from the mixture by lowering the pressure. The mixture was wet-purified using hexane and ethyl acetate to obtain the compound B-4 (13 g, 33.90 mmol). (yield: 74%) 
     (2) Synthesis of Compound C-4 
     
       
         
         
             
             
         
       
     
     The compound B-4 (10 g, 26.07 mmol) and THF (100 mL) were added, and CH 3 MgBr (15.5 g, 130 mmol) was slowly added at 0° C. The reaction was proceeded for 12 hours, and the mixture was worked-up using ethyl acetate and MgSO 4 . The mixture was wet-purified using hexane and ethyl acetate, and the compound C-4 (6 g, 16.24 mmol) was obtained. (yield: 62%) 
     (3) Synthesis of Compound D-4 
     
       
         
         
             
             
         
       
     
     The compound C-4 (20 g, 54.12 mmol) was added to a mixed aqueous solution of acetic acid and sulfuric acid (200 mL), and the mixture was reflux for 16 hours. After completion of the reaction, a cold sodium hydroxide aqueous solution was slowly added into the mixture. The mixture was worked-up using dichloromethane and MgSO 4 . The mixture was recrystallized using toluene and ethanol to obtain the compound D-4 (10 g, 28.45 mmol) in a yellow solid state. (yield: 53%) 
     (4) Synthesis of Compound E-4 
     
       
         
         
             
             
         
       
     
     The compound D-4 (10 g, 28.45 mmol), 2-ethoxyethanol (200 mL) and distilled water (50 mL) were added, and nitrogen was injected to the mixture for 1 hour. IrCl 3 .H 2 O (4.5 g, 14.22 mmol) was put in the reaction vessel and refluxed for 2 days. After completion of the reaction, the temperature was slowly lowered to room temperature and the resulting solid was filtered. After washing the solid with methanol and drying the solid, the compound E-4 (6.0 g, 5.19 mmol) was obtained. (yield: 18%) 
     (5) Synthesis of Compound RD4 
     
       
         
         
             
             
         
       
     
     The compound E-4 (10 g, 8.64 mmol), 3,7-diethylnonane-4,6-dione (18.3 g, 86.4 mmol) and Na 2 CO 3  (18.3 g, 172.8 mmol) were added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol and stirred, and then the filtered solid was dried. The mixture was recrystallized and purified using dichloromethane and isopropanol to obtain the compound RD4 with high purity (4 g, 3.62 mmol). (yield: 42%) 
     Synthesis Example 17: Synthesis of Compound RD17 (Compound 610 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     The compound A-17 (10 g, 5.38 mmol), 3,7-diethyl-3,7-dimethylnonane-4,6-dione (12.94 g, 53.84 mmol) and Na 2 CO 3  (11.4 g, 107.7 mmol) were added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol and stirred, and then the filtered solid was dried. The mixture was recrystallized using dichloromethane and isopropanol and purified to obtain the compound RD17 with high purity (3.8 g, 3.36 mmol). (yield: 42%) 
     Synthesis Example 18: Synthesis of Compound RD18 (Compound 611 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, bromobenzene (1.01 g, 6.46 mmol) and 50 ml of THF were put in a reaction vessel, and the temperature was lowered to −78° C. n-BuLi (2.6 ml, 2.5M in hexane) was slowly added into the mixture. After 30 minutes, while maintaining the temperature, N,N′-diisopropylcarbodiimide (0.82 g, 6.46 mmol) was slowly added, and the mixture was stirred for 30 minutes. The mixture was added to a reaction vessel, in which the compound A-18 (3 g, 1.62 mmol) was dissolved in 100 ml THF, and stirred at 80° C. for 8 hours. The temperature of the mixture was lowered to room temperature and volatile substances were removed. After the mixture was recrystallized using THF/pentane and dichloromethane/hexane, purification was performed to obtain the compound RD18 with high purity (2.3 g, 2.03 mmol). 
     Synthesis Example 19: Synthesis of Compound RD19 (Compound 612 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-19 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-1 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD19 with high purity (1.1 g, 1.01 mmol). 
     Synthesis Example 20: Synthesis of Compound RD20 (Compound 613 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-20 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-2 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD20 with high purity (0.9 g, 0.80 mmol). 
     Synthesis Example 21: Synthesis of Compound RD21 (Compound 614 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     The compound A-21 (10 g, 5.38 mmol), 3,7-diethyl-3,7-dimethylnonane-4,6-dione (12.94 g, 53.84 mmol) and Na 2 CO 3  (11.4 g, 107.7 mmol) were added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol and stirred, and then the filtered solid was dried. The mixture was recrystallized using dichloromethane and isopropanol and purified to obtain the compound RD21 with high purity (3.4 g, 3.00 mmol). 
     Synthesis Example 22: Synthesis of Compound RD22 (Compound 615 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, bromobenzene (1.01 g, 6.46 mmol) and 50 ml of THF were put in a reaction vessel, and the temperature was lowered to −78° C. n-BuLi (2.6 ml, 2.5M in hexane) was slowly added into the mixture. After 30 minutes, while maintaining the temperature, N,N′-diisopropylcarbodiimide (0.82 g, 6.46 mmol) was slowly added, and the mixture was stirred for 30 minutes. The mixture was added to a reaction vessel, in which the compound A-22 (3 g, 1.62 mmol) was dissolved in 100 ml THF, and stirred at 80° C. for 8 hours. The temperature of the mixture was lowered to room temperature and volatile substances were removed. After the mixture was recrystallized using THF/pentane and dichloromethane/hexane, purification was performed to obtain the compound RD22 with high purity (2.0 g, 1.82 mmol). 
     Synthesis Example 23: Synthesis of Compound RD23 (Compound 616 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-23 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-1 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD23 with high purity (2.5 g, 2.29 mmol). 
     Synthesis Example 24: Synthesis of Compound RD24 (Compound 617 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-24 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-2 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD24 with high purity (2.2 g, 1.95 mmol). 
     Synthesis Example 25: Synthesis of Compound RD25 (Compound 618 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     The compound A-25 (10 g, 5.38 mmol), 3,7-diethyl-3,7-dimethylnonane-4,6-dione (12.94 g, 53.84 mmol) and Na 2 CO 3  (11.4 g, 107.7 mmol) were added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol and stirred, and then the filtered solid was dried. The mixture was recrystallized using dichloromethane and isopropanol and purified to obtain the compound RD25 with high purity (3.3 g, 2.91 mmol). 
     Synthesis Example 26: Synthesis of Compound RD26 (Compound 619 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, bromobenzene (1.01 g, 6.46 mmol) and 50 ml of THF were put in a reaction vessel, and the temperature was lowered to −78° C. n-BuLi (2.6 ml, 2.5M in hexane) was slowly added into the mixture. After 30 minutes, while maintaining the temperature, N,N′-diisopropylcarbodiimide (0.82 g, 6.46 mmol) was slowly added, and the mixture was stirred for 30 minutes. The mixture was added to a reaction vessel, in which the compound A-26 (3 g, 1.62 mmol) was dissolved in 100 ml THF, and stirred at 80° C. for 8 hours. The temperature of the mixture was lowered to room temperature and volatile substances were removed. After the mixture was recrystallized using THF/pentane and dichloromethane/hexane, purification was performed to obtain the compound RD26 with high purity (2.1 g, 1.92 mmol). 
     Synthesis Example 27: Synthesis of Compound RD27 (Compound 620 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-27 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-1 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD27 with high purity (2.2 g, 2.02 mmol). 
     Synthesis Example 28: Synthesis of Compound RD28 (Compound 621 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-28 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-2 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD28 with high purity (1.9 g, 1.68 mmol). 
     Synthesis Example 29: Synthesis of Compound RD29 (Compound 622 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     The compound A-29 (10 g, 5.38 mmol), 3,7-diethyl-3,7-dimethylnonane-4,6-dione (12.94 g, 53.84 mmol) and Na 2 CO 3  (11.4 g, 107.7 mmol) were added and dissolved in 2-ethoxyethanol (100 mL). The mixture was slowly stirred for 24 hours. After completion of the reaction, the product was filtered using dichloromethane. After removing the solvent, the solid was filtered. The filtered solid was added to isopropanol and stirred, and then the filtered solid was dried. The mixture was recrystallized using dichloromethane and isopropanol and purified to obtain the compound RD29 with high purity (3.9 g, 3.44 mmol). 
     Synthesis Example 30: Synthesis of Compound RD30 (Compound 623 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, bromobenzene (1.01 g, 6.46 mmol) and 50 ml of THF were put in a reaction vessel, and the temperature was lowered to −78° C. n-BuLi (2.6 ml, 2.5M in hexane) was slowly added into the mixture. After 30 minutes, while maintaining the temperature, N,N′-diisopropylcarbodiimide (0.82 g, 6.46 mmol) was slowly added, and the mixture was stirred for 30 minutes. The mixture was added to a reaction vessel, in which the compound A-30 (3 g, 1.62 mmol) was dissolved in 100 ml THF, and stirred at 80° C. for 8 hours. The temperature of the mixture was lowered to room temperature and volatile substances were removed. After the mixture was recrystallized using THF/pentane and dichloromethane/hexane, purification was performed to obtain the compound RD30 with high purity (2.7 g, 2.46 mmol). 
     Synthesis Example 31: Synthesis of Compound RD31 (Compound 624 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-31 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-1 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD31 with high purity (2.0 g, 1.84 mmol). 
     Synthesis Example 32: Synthesis of Compound RD32 (Compound 625 in Formula 1-29) 
     
       
         
         
             
             
         
       
     
     Under the nitrogen condition, the compound A-32 (3 g, 1.62 mmol) and THT (100 ml) were added in a reaction vessel, and the compound F-2 (0.8 g, 3.56 mmol) dissolved in THF was slowly added. The mixture was stirred at room temperature for 8 hours. The mixture was extracted using toluene, the solvent was removed, and diethyl ether was added to obtain a solid. The obtained solid was purified to obtain the compound RD32 with high purity (1.8 g, 1.59 mmol). 
     The second compound  234  has an excellent hole-dominant property (characteristic) and is represented by Formula 2-1. 
     
       
         
         
             
             
         
       
     
     wherein
 
one of X 12  and X 13  is a nitrogen atom (N), and the other one of X 12  and X 13  is an oxygen atom (O) or a sulfur atom (S);
 
each of R 4 , R 5  and R 6  is independently selected from the group consisting of an unsubstituted or substituted C 6 -C 30  aryl group and an unsubstituted or substituted C 3 -C 30  heteroaryl group; L is selected from the group consisting of an unsubstituted or substituted C 6 -C 30  arylene group and an unsubstituted or substituted C 3 -C 30  heteroarylene group; and a is 0 or 1.
 
     For example, R 4 , R 5  and R 6  may be same or different. The C 6 -C 30  aryl group, the C 3 -C 30  heteroaryl group, the C 6 -C 30  arylene group and the C 3 -C 30  heteroarylene group may be substituted with a C 1 -C 10  alkyl group or a C 6 -C 30  aryl group. 
     For example, R 4  may be selected from an unsubstituted or substituted C 6 -C 30  aryl. L may be selected from an unsubstituted or substituted C 6 -C 30  arylene group, or a may be 0. 
     In an exemplary embodiment, R 4  may be an unsubstituted C 6 -C 30  aryl group, e.g., phenyl. Each of R 5  and R 6  may be independently selected from the group consisting of a substituted unsubstituted C 6 -C 30  aryl group, e.g., phenyl, naphthyl or biphenyl, a substituted C 6 -C 30  aryl group, e.g., 9,9-dimethylfluorenyl, and an unsubstituted C 3 -C 30  heteroaryl group, e.g., dibenzofuranyl or dibenzothiophenyl. L may be a substituted C 6 -C 30  arylene group, e.g., phenylene. 
     In an exemplary embodiment, one of X 12  and X 13  may be N, and the other one of X 12  and X 13  may be 0, and each of R 4 , R 5  and R 6  may be an unsubstituted or substituted C 6 -C 30  aryl group. 
     In an exemplary embodiment, R 4  may be phenyl. R 5  and R 6  may be different, R 5  may be phenyl or biphenyl, and R 6  may be independently selected from naphthyl, biphenyl and 9,9-dimethylfluorenyl. 
     For example, the second compound  234  can be one of the compounds in Formula 2-2. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The third compound  236  has an excellent electron-dominant property (characteristic) and is represented by Formula 3-1. 
     
       
         
         
             
             
         
       
     
     wherein
 
X is NR 8 , O or S, and R 8  is selected from the group consisting of an unsubstituted or substituted C 1 -C 10  alkyl group, an unsubstituted or substituted C 6 -C 30  aryl group and an unsubstituted or substituted C 3 -C 30  heteroaryl group, and
 
R 7  is selected from the group consisting of an unsubstituted or substituted C 6 -C 30  aryl group and an unsubstituted or substituted C 3 -C 30  heteroaryl group.
 
     For example, each of R 7  and R 8  may be independently selected from an unsubstituted or substituted C 6 -C 30  aryl group. 
     In an exemplary embodiment, R 7  may be selected from phenyl, biphenyl, naphthyl and 9,9-dimethylfluorenyl, and R 8  may be selected from phenyl, naphthyl and biphenyl. 
     In Formula 3-1, a linking position (or a linking site) of a X-containing fused-ring to a benzocarbazole moiety (or a naphtho benzofuran moiety) can be specified. Namely, 
     Formula 3-1 can be represented by Formula 3-2. 
     
       
         
         
             
             
         
       
     
     In Formula 3-1, a linking position between a X-containing fused-ring and a benzocarbazole moiety (or a naphtho benzofuran moiety) can be specified. Namely, Formula 3-1 can be represented by Formula 3-3. 
     
       
         
         
             
             
         
       
     
     For example, the third compound  236  can be one of the compounds in Formula 3-4. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The HIL  210  is positioned between the first electrode  160  and the HTL  220 . The HIL  210  can include at least one compound selected from the group consisting of 4,4′,4″-tris(3-methylphenylamino)triphenylamine (MTDATA), 4,4′,4″-tris(N,N-diphenyl-amino)triphenylamine (NATA), 4,4′,4″-tris(N-(naphthalene-1-yl)-N-phenyl-amino)triphenylamine (1T-NATA), 4,4′,4″-tris(N-(naphthalene-2-yl)-N-phenyl-amino)triphenylamine (2T-NATA), copper phthalocyanine (CuPc), tris(4-carbazoyl-9-yl-phenyl)amine (TCTA), N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine (NPB or NPD), 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile(dipyrazino[2,3-f: 2′3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN), 1,3,5-tris[4-(diphenylamino)phenyl]benzene (TDAPB), poly(3,4-ethylenedioxythiphene)polystyrene sulfonate (PEDOT/PSS), and N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine, but it is not limited thereto. The HIL  210  can have a thickness of 10 to 200 Å, preferably 50 to 150 Å. 
     The HTL  220  is positioned between the HIL  210  and the red EML  230 . The HTL  220  can include at least one compound selected from the group consisting of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), NPB (or NPD), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl(CBP), poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine](poly-TPD), (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine))] (TFB), di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane (TAPC), 3,5-di(9H-carbazol-9-yl)-N,N-diphenylaniline (DCDPA), N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine, N-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine, and a compound in Formula 4, but it is not limited thereto. The HTL  220  can have a thickness of 500 to 900 Å, preferably 600 to 800 Å. 
     
       
         
         
             
             
         
       
     
     The ETL  240  is positioned between the red EML  230  and the second electrode  164  and includes at least one of an oxadiazole-containing compound, a triazole-containing compound, a phenanthroline-containing compound, a benzoxazole-containing compound, a benzothiazole-containing compound, a benzimidazole-containing compound, and a triazine-containing compound. For example, the ETL  240  can include at least one compound selected from the group consisting of tris-(8-hydroxyquinoline aluminum (Alq 3 ),2-biphenyl-4-yl-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD), spiro-PBD, lithium quinolate (Liq), 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBi), bis(2-methyl-8-quinolinolato-N1,O8)-(1,1′-biphenyl-4-olato)aluminum (BAlq), 4,7-diphenyl-1,10-phenanthroline (Bphen), 2,9-bis(naphthalene-2-yl)-4,7-diphenyl-1,10-phenanthroline (NBphen), 2,9-dimethyl-4,7-diphenyl-1,10-phenathroline (BCP), 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ), 4-(naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole (NTAZ), 1,3,5-tri(p-pyrid-3-yl-phenyl)benzene (TpPyPB), 2,4,6-tris(3′-(pyridin-3-yl)biphenyl-3-yl)1,3,5-triazine (TmPPPyTz), Poly[9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene]-alt-2,7-(9,9-dioctylfluorene)](PFNBr), tris(phenylquinoxaline) (TPQ), and diphenyl-4-triphenylsilyl-phenylphosphine oxide (TSPO1), but it is not limited thereto. The ETL  240  can have a thickness of 100 to 500 Å, preferably 200 to 400 Å. 
     The EIL  250  is positioned between the ETL  240  and the second electrode  164 . The EIL  250  at least one of an alkali halide compound, such as LiF, CsF, NaF, or BaF 2 , and an organo-metallic compound, such as Liq, lithium benzoate, or sodium stearate, but it is not limited thereto. The EIL  250  can have a thickness of 1 to 20 Å, preferably 5 to 15 Å. 
     The EBL, which is positioned between the HTL  220  and the red EML  230  to block the electron transfer from the red EML  230  to the HTL  220 , can include at least one compound selected from the group consisting of TCTA, tris[4-(diethylamino)phenyl]amine, N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine, TAPC, MTDATA, 1,3-bis(carbazol-9-yl)benzene (mCP), 3,3′-bis(N-carbazolyl)-1,1′-biphenyl (mCBP), CuPc, N,N′-bis[4-[bis(3-methylphenyl)amino]phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (DNTPD), TDAPB, DCDPA, and 2,8-bis(9-phenyl-9H-carbazol-3-yl)dibenzo[b,d]thiophene), but it is not limited thereto. 
     The HBL, which is positioned between the ETL  240  and the red EML  230  to block the hole transfer from the red EML  230  to the ETL  240 , can include the above material of the ETL  240 . For example, the material of the HBL has a HOMO energy level being lower than a material of the red EML  230  and can be at least one compound selected from the group consisting of BCP, BAlq, Alq3, PBD, spiro-PBD, Liq, bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimidine (B3PYMPM), bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO), 9-(6-9H-carbazol-9-yl)pyridine-3-yl)-9H-3,9′-bicarbazole, and TSPO1, but it is not limited thereto. 
     As illustrated above, the OLED D1 is positioned in the red pixel region, and the red EML  230  of the OLED D1 includes the first compound  232 , which is represented by Formula 1-1, being a dopant, the second compound  234 , which is represented by Formula 2-1, being a first host or a p-type host and the third compound  236 , which is represented by Formula 3-1, being a second host or an n-type host. As a result, in the OLED D1, the driving voltage is decreased, and the luminous efficiency and the luminous lifespan is increased. 
       FIG.  4    is a cross-sectional view illustrating an OLED according to a third embodiment of the present disclosure. 
     As shown in  FIG.  4   , the OLED D2 includes first and second electrodes  160  and  164  facing each other and the organic emitting layer  162  therebetween. The organic emitting layer  162  includes a first emitting part  710  including a first red EML  720  and a second emitting part  730  including a second red EML  740 . In addition, the organic emitting layer  162  can further include a charge generation layer (CGL)  750  between the first and second emitting parts  710  and  730 . 
     For example, the first electrode  160  can include a transparent conductive material, e.g., ITO or IZO, and the second electrode  164  can include one of Al, Mg, Ag, AlMg and MgAg. 
     The CGL  750  is positioned between the first and second emitting parts  710  and  730  so that the first emitting part  710 , the CGL  750  and the second emitting part  730  are sequentially stacked on the first electrode  160 . Namely, the first emitting part  710  is positioned between the first electrode  160  and the CGL  750 , and the second emitting part  730  is positioned between the second electrode  164  and the CGL  750 . 
     As illustrated below, the first emitting part  710  includes the first red EML  720 . The first red EML  720  includes a first compound  722  as a red dopant (e.g., a red emitter), a second compound  724  as a p-type host (e.g., a first host) and a third compound  726  as an n-type host (e.g., a second host). In the first red EML  720 , the first compound  722  is represented by Formula 1-1, the second compound  724  is represented by Formula 2-1, and the third compound  726  is represented by Formula 3-1. 
     The first red EML  720  can have a thickness of 100 to 400 Å, e.g., 200 to 400 Å, but it is not limited thereto. 
     In the first red EML  720 , each of the second and third compounds  724  and  726  can have a weight % being greater than the first compound  722 . For example, in the first red EML  720 , the first compound  722  can have a weight % of 1 to 20, e.g., 5 to 15. 
     In addition, in the first red EML  720 , a ratio of the weight % between the second compound  724  and the third compound  726  can be 1:3 to 3:1. For example, in the first red EML  720 , the second and third compounds  724  and  726  can have the same weight %. 
     The first emitting part  710  can further include at least one of a first HTL  714  under the first red EML  720  and a first ETL  716  on or over the first red EML  720 . Namely, the first HTL  714  is disposed between the first red EML  720  and the first electrode  160 , and the first ETL  716  is disposed between the first red EML  720  and the CGL  750 . 
     In addition, the first emitting part  710  can further include an HIL  712  between the first electrode  160  and the first HTL  714 . 
     As illustrated below, the second emitting part  730  includes the second red EML  740 . The second red EML  740  includes a first compound  742 , e.g., a fourth compound, as a red dopant (e.g., a red emitter), a second compound  744 , e.g., a fifth compound, as a p-type host (e.g., a first host) and a third compound  726 , e.g., a sixth compound, as an n-type host (e.g., a second host). In the second red EML  740 , the first compound  742  is represented by Formula 1-1, the second compound  744  is represented by Formula 2-1, and the third compound  746  is represented by Formula 3-1. 
     The second red EML  740  can have a thickness of 100 to 400 Å, e.g., 200 to 400 Å, but it is not limited thereto. 
     In the second red EML  740 , each of the second and third compounds  744  and  746  can have a weight % being greater than the first compound  742 . For example, in the second red EML  740 , the first compound  742  can have a weight % of 1 to 20, e.g., 5 to 15. 
     In addition, in the second red EML  740 , a ratio of the weight % between the second compound  744  and the third compound  746  can be 1:3 to 3:1. For example, in the second red EML  740 , the second and third compounds  744  and  746  can have the same weight %. 
     The first compound  742  in the second red EML  740  and the first compound  722  in the first red EML  720  can be same or different. The second compound  744  in the second red EML  740  and the second compound  724  in the first red EML  720  can be same or different. The third compound  746  in the second red EML  740  and the third compound  726  in the first red EML  720  can be same or different. 
     The second emitting part  730  can further include at least one of a second HTL  732  under the second red EML  740  and a second ETL  734  on or over the second red EML  740 . Namely, the second HTL  732  is disposed between the second red EML  740  and the CGL  750 , and the second ETL  734  is disposed between the second red EML  740  and the second electrode  164 . 
     In addition, the second emitting part  730  can further include an EIL  736  between the second ETL  734  and the second electrode  164 . 
     The CGL  750  is positioned between the first and second emitting parts  710  and  730 . 
     Namely, the first and second emitting parts  710  and  730  are connected to each other through the CGL  750 . The CGL  750  can be a P-N junction type CGL of an N-type CGL  752  and a P-type CGL  754 . 
     The N-type CGL  752  is positioned between the first ETL  716  and the second HTL  732 , and the P-type CGL  754  is positioned between the N-type CGL  752  and the second HTL  732 . 
     In the OLED D2, at least one of the first and second red EMLs  720  and  740  includes a first compound, e.g., a red dopant, represented by Formula 1-1, a second compound, e.g., a p-type host, represented by Formula 2-1 and a third compound, e.g., an n-type host, represented by Formula 3-1. As a result, the OLED D2 has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
       FIG.  5    is a cross-sectional view illustrating an organic light emitting display device according to a fourth embodiment of the present disclosure. 
     As shown in  FIG.  5   , the organic light emitting display device  300  includes a first substrate  310 , where a red pixel region RP, a green pixel region GP and a blue pixel region BP are defined, a second substrate  370  facing the first substrate  310 , an OLED D, which is positioned between the first and second substrates  310  and  370  and providing white emission, and a color filter layer  380  between the OLED D and the second substrate  370 . 
     Each of the first and second substrates  310  and  370  can be a glass substrate or a flexible substrate. For example, each of the first and second substrates  310  and  370  can be a polyimide (PI) substrate, a polyethersulfone (PES) substrate, a polyethylenenaphthalate (PEN) substrate, a polyethylene terephthalate (PET) substrate or a polycarbonate (PC) substrate. 
     A buffer layer  320  is formed on the substrate, and the TFT Tr corresponding to each of the red, green and blue pixel regions RP, GP and BP is formed on the buffer layer  320 . The buffer layer  320  can be omitted. 
     A semiconductor layer  322  is formed on the buffer layer  320 . The semiconductor layer  322  can include an oxide semiconductor material or polycrystalline silicon. 
     A gate insulating layer  324  is formed on the semiconductor layer  322 . The gate insulating layer  324  can be formed of an inorganic insulating material such as silicon oxide or silicon nitride. 
     A gate electrode  330 , which is formed of a conductive material, e.g., metal, is formed on the gate insulating layer  324  to correspond to a center of the semiconductor layer  322 . 
     An interlayer insulating layer  332 , which is formed of an insulating material, is formed on the gate electrode  330 . The interlayer insulating layer  332  can be formed of an inorganic insulating material, e.g., silicon oxide or silicon nitride, or an organic insulating material, e.g., benzocyclobutene or photo-acryl. 
     The interlayer insulating layer  332  includes first and second contact holes  334  and  336  exposing both sides of the semiconductor layer  322 . The first and second contact holes  334  and  336  are positioned at both sides of the gate electrode  330  to be spaced apart from the gate electrode  330 . 
     A source electrode  340  and a drain electrode  342 , which are formed of a conductive material, e.g., metal, are formed on the interlayer insulating layer  332 . 
     The source electrode  340  and the drain electrode  342  are spaced apart from each other with respect to the gate electrode  330  and respectively contact both sides of the semiconductor layer  322  through the first and second contact holes  334  and  336 . 
     The semiconductor layer  322 , the gate electrode  330 , the source electrode  340  and the drain electrode  342  constitute the TFT Tr. The TFT Tr serves as a driving element. Namely, the TFT Tr can correspond to the driving TFT Td (of  FIG.  1   ). 
     The gate line and the data line cross each other to define the pixel, and the switching TFT is formed to be connected to the gate and data lines. The switching TFT is connected to the TFT Tr as the driving element. 
     In addition, the power line, which can be formed to be parallel to and spaced apart from one of the gate and data lines, and the storage capacitor for maintaining the voltage of the gate electrode of the TFT Tr in one frame can be further formed. 
     A planarization layer  350 , which includes a drain contact hole  352  exposing the drain electrode  342  of the TFT Tr, is formed to cover the TFT Tr. 
     A first electrode  360 , which is connected to the drain electrode  342  of the TFT Tr through the drain contact hole  352 , is separately formed in each pixel region and on the planarization layer  350 . The first electrode  360  can be an anode and can be formed of a conductive material, e.g., a transparent conductive oxide (TCO), having a relatively high work function. The first electrode  360  can further include a reflection electrode or a reflection layer. For example, the reflection electrode or the reflective layer can include Ag or aluminum-palladium-copper (APC). In a top-emission type organic light emitting display device  300 , the first electrode  360  can have a structure of ITO/Ag/ITO or ITO/APC/ITO. 
     A bank layer  366  is formed on the planarization layer  350  to cover an edge of the first electrode  360 . Namely, the bank layer  366  is positioned at a boundary of the pixel and exposes a center of the first electrode  360  in the pixel. Since the OLED D emits the white light in the red, green and blue pixel regions RP, GP and BP, the organic emitting layer  362  can be formed as a common layer in the red, green and blue pixel regions RP, GP and BP without separation. The bank layer  366  can be formed to prevent a current leakage at an edge of the first electrode  360  and can be omitted. 
     An organic emitting layer  362  is formed on the first electrode  360 . As illustrated below, the organic emitting layer  362  includes at least two emitting parts, and each emitting part includes at least one EML. As a result, the OLED D emits the white light. 
     At least one of the emitting parts includes a first compound, e.g., a red dopant, represented by Formula 1-1, a second compound, e.g., a p-type host or a first host, represented by Formula 2-1 and a third compound, e.g., an n-type host or a second host, represented by Formula 3-1 to emit the red light. 
     A second electrode  364  is formed over the substrate  310  where the organic emitting layer  362  is formed. 
     In the organic light emitting display device  300 , since the light emitted from the organic emitting layer  362  is incident to the color filter layer  380  through the second electrode  364 , the second electrode  364  has a thin profile for transmitting the light. 
     The first electrode  360 , the organic emitting layer  362  and the second electrode  364  constitute the OLED D. 
     The color filter layer  380  is positioned over the OLED D and includes a red color filter  382 , a green color filter  384  and a blue color filter  386  respectively corresponding to the red, green and blue pixel regions RP, GP and BP. The red color filter  382  can include at least one of red dye and red pigment, the green color filter  384  can include at least one of green dye and green pigment, and the blue color filter  386  can include at least one of blue dye and blue pigment. 
     The color filter layer  380  can be attached to the OLED D by using an adhesive layer. Alternatively, the color filter layer  380  can be formed directly on the OLED D. 
     An encapsulation film can be formed to prevent penetration of moisture into the OLED D. For example, the encapsulation film can include a first inorganic insulating layer, an organic insulating layer and a second inorganic insulating layer sequentially stacked, but it is not limited thereto. The encapsulation film can be omitted. 
     A polarization plate for reducing an ambient light reflection can be disposed over the top-emission type OLED D. For example, the polarization plate can be a circular polarization plate. 
     In the OLED of  FIG.  5   , the first and second electrodes  360  and  364  are a reflection electrode and a transparent (or semi-transparent) electrode, respectively, and the color filter layer  380  is disposed over the OLED D. Alternatively, when the first and second electrodes  360  and  364  are a transparent (or semi-transparent) electrode and a reflection electrode, respectively, the color filter layer  380  can be disposed between the OLED D and the first substrate  310 . 
     A color conversion layer can be formed between the OLED D and the color filter layer  380 . The color conversion layer can include a red color conversion layer, a green color conversion layer and a blue color conversion layer respectively corresponding to the red, green and blue pixel regions RP, GP and BP. The white light from the OLED D is converted into the red light, the green light and the blue light by the red, green and blue color conversion layer, respectively. For example, the color conversion layer can include a quantum dot. Accordingly, the color purity of the organic light emitting display device  300  can be further improved. 
     The color conversion layer can be included instead of the color filter layer  380 . 
     As described above, in the organic light emitting display device  300 , the OLED D in the red, green and blue pixel regions RP, GP and BP emits the white light, and the white light from the organic light emitting diode D passes through the red color filter  382 , the green color filter  384  and the blue color filter  386 . As a result, the red light, the green light and the blue light are provided from the red pixel region RP, the green pixel region GP and the blue pixel region BP, respectively. 
     In  FIG.  5   , the OLED D emitting the white light is used for a display device. 
     Alternatively, the OLED D can be formed on an entire surface of a substrate without at least one of the driving element and the color filter layer to be used for a lightening device. The display device and the lightening device each including the OLED D of the present disclosure can be referred to as an organic light emitting device. 
       FIG.  6    is a cross-sectional view illustrating an OLED according to a fifth embodiment of the present disclosure. 
     As shown in  FIG.  6   , in the OLED D3, the organic emitting layer  362  includes a first emitting part  430  including a red EML  410 , a second emitting part  440  including a first blue EML  450  and a third emitting part  460  including a third blue EML  470 . In addition, the organic emitting layer  362  can further include a first CGL  480  between the first and second emitting parts  430  and  440  and a second CGL  490  between the first and third emitting part  430  and  460 . In addition, the first emitting part  430  can further include a green EML  420 . 
     The first electrode  360  is an anode, and the second electrode  364  is a cathode. One of the first and second electrodes  360  and  364  can be a transparent (semitransparent) electrode, and the other one of the first and second electrodes  360  and  364  can be a reflective electrode. 
     The second emitting part  440  is positioned between the first electrode  360  and the first emitting part  430 , and the third emitting part  460  is positioned between the first emitting part  430  and the second electrode  364 . In addition, the second emitting part  440  is positioned between the first electrode  360  and the first CGL  480 , and the third emitting part  460  is positioned between the second CGL  490  and the second electrode  364 . Namely, the second emitting part  440 , the first CGL  480 , the first emitting part  430 , the second CGL  460  and the third emitting part  460  are sequentially stacked on the first electrode  360 . 
     In the first emitting part  430 , the green EML  420  is positioned on the red EML  410 . 
     The first emitting part  430  can further include at least one of a first HTL  432  under the red EML  410  and a first ETL  434  over the red EML  410 . When the first emitting part  430  includes the green EML  420 , the first ETL  434  is positioned on the green EML  420 . 
     The second emitting part  440  can further include at least one of a second HTL  444  under the first blue EML  450  and a second ETL  448  on the first blue EML  450 . In addition, the second emitting part  440  can further include an HIL  442  between the first electrode  360  and the first HTL  444 . 
     The second emitting part  440  can further include at least one of a first EBL between the second HTL  444  and the first blue EML  450  and a first HBL between the first blue EML  450  and the second ETL  448 . 
     The third emitting part  460  can further include at least one of a third HTL  462  under the second blue EML  470  and a third ETL  466  on the second blue EML  470 . In addition, the third emitting part  460  can further include an EIL  468  between the second electrode  364  and the third ETL  466 . 
     The third emitting part  460  can further include at least one of a first EBL between the third HTL  462  and the second blue EML  470  and a first HBL between the second blue EML  470  and the third ETL  466 . 
     For example, the HIL  442  can include at least one of MTDATA, NATA, 4,4′,4″-tris(N-(naphthalene-1-yl)-N-phenyl-amino)triphenylamine 1T-NATA, 2T-NATA, CuPc, TCTA, NPB, HAT-CN, TDAPB, PEDOT/PSS and N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine. 
     Each of the first to third HTLs  432 ,  444  and  464  can include at least one of TPD, NPB, CBP, poly-TPD, TFB, TAPC, DCDPA, N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine, N-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine, and the compound in Formula 4. 
     Each of the first to third ETLs  434 ,  448  and  466  can include at least one of Alq3, PBD, spiro-PBD, Liq, TPBi, BAlq, Bphen, NBphen, BCP, TAZ, NTAZ, TpPyPB, TmPPPyTz, PFNBr, TPQ, and TSPO1. 
     The EIL  468  can include at least one of an alkali halide compound, such as LiF, CsF, NaF, or BaF 2 , and an organo-metallic compound, such as Liq, lithium benzoate, or sodium stearate. 
     The first CGL  480  is positioned between the first and second emitting parts  430  and  440 , and the second CGL  490  is positioned between the first and third emitting parts  430  and  460 . Namely, the first and second emitting parts  430  and  440  is connected to each other by the first CGL  480 , and the first and third emitting parts  430  and  460  is connected to each other by the second CGL  490 . The first CGL  480  can be a P-N junction type CGL of an N-type CGL  482  and a P-type CGL  484 , and the second CGL  490  can be a P-N junction type CGL of an N-type CGL  492  and a P-type CGL  494 . 
     In the first CGL  480 , the N-type CGL  482  is positioned between the first HTL  432  and the second ETL  448 , and the P-type CGL  484  is positioned between the N-type CGL  482  and the first HTL  432 . 
     In the second CGL  490 , the N-type CGL  492  is positioned between the first ETL  434  and the third HTL  462 , and the P-type CGL  494  is positioned between the N-type CGL  492  and the third HTL  462 . 
     Each of the N-type CGL  482  of the first CGL  480  and the N-type CGL  492  of the second CGL  490  can be an organic layer doped with an alkali metal, e.g., Li, Na, K or Cs, and/or an alkali earth metal, e.g., Mg, Sr, Ba or Ra. For example, each of the N-type CGL  482  of the first CGL  480  and the N-type CGL  492  of the second CGL  490  can include an organic material, e.g., 4,7-diphenyl-1,10-phenanthroline (Bphen) or MTDATA, as a host, and the alkali metal and/or the alkali earth metal as a dopant can be doped with a weight % of about 0.01 to 30. 
     Each of the P-type CGL  484  of the first CGL  480  and the P-type CGL  494  of the second CGL  490  can include at least one of an inorganic material, which is selected from the group consisting of tungsten oxide (WOx), molybdenum oxide (MoOx), beryllium oxide (Be2O3), vanadium oxide (V2O5) and their combination, and an organic material, which is selected from the group consisting of NPD, HAT-CN, F4TCNQ, TPD, N,N,N′,N′-tetranaphthyl-benzidine (TNB), TCTA, N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) and their combination. 
     The red EML  410  includes a first compound  412  as a red dopant (e.g., a red emitter), a second compound  414  as a p-type host (e.g., a first host) and a third compound  416  as an n-type host (e.g., a second host). In the red EML  410 , the first compound  412  is represented by Formula 1-1, the second compound  414  is represented by Formula 2-1, and the third compound  416  is represented by Formula 3-1. 
     In the red EML  410 , each of the second and third compounds  414  and  416  can have a weight % being greater than the first compound  412 . For example, in the red EML  410 , the first compound  412  can have a weight % of 1 to 20, e.g., 5 to 15. 
     In addition, in the red EML  410 , a ratio of the weight % between the second compound  414  and the third compound  416  can be 1:3 to 3:1. For example, in the red EML  410 , the second and third compounds  414  and  416  can have the same weight %. 
     In the first emitting part  410 , the green EML  420  includes a green host and a green dopant. The green dopant can be one of a phosphorescent compound, a fluorescent compound and a delayed fluorescent compound. For example, in the green EML  420 , the host can be 4,4′-bis(carbazol-9-yl)biphenyl (CBP), and the green dopant can be fac tris(2-phenylpyridine)iridium Ir(ppy)3 or tris(8-hydroxyquinolino)aluminum (Alq3). 
     The first blue EML  450  in the second emitting part  440  includes a first blue host and a first blue dopant, and the second blue EML  470  in the third emitting part  460  includes a second blue host and a second blue dopant. 
     For example, each of the first and second blue hosts can be independently selected from the group consisting of mCP, 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazole-3-carbonitrile (mCP-CN), mCBP, CBP-CN, 9-(3-(9H-Carbazol-9-yl)phenyl)-3-(diphenylphosphoryl)-9H-carbazole (mCPPO1) 3,5-Di(9H-carbazol-9-yl)biphenyl (Ph-mCP), TSPO1, 9-( 3 ′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3-yl)-9H-pyrido[2,3-b]indole (CzBPCb), bis(2-methylphenyl)diphenylsilane (UGH-1), 1,4-bis(triphenylsilyl)benzene (UGH-2), 1,3-bis(triphenylsilyl)benzene (UGH-3), 9,9-spiorobifluoren-2-yl-diphenyl-phosphine oxide (SPPO1) and 9,9′-(5-(triphenylsilyl)-1,3-phenylene)bis(9H-carbazole) (SimCP). 
     For example, each of the first and second blue dopants can be independently selected from the group consisting of perylene, 4,4′-bis[4-(di-p-tolylamino)styryl]biphenyl (DPAVBi), 4-(di-p-tolylamino)-4-4′-[(di-p-tolylamino)styryl]stilbene (DPAVB), 4,4′-bis[4-(diphenylamino)styryl]biphenyl (BDAVBi), 2,7-bis(4-diphenylamino)styryl)-9,9-spiorfluorene (spiro-DPVBi), [1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl] benzene (DSB), 1-4-di-[4-(N,N-diphenyl)amino]styryl-benzene (DSA), 2,5,8,11-tetra-tetr-butylperylene (TBPe), bis(2-hydroxylphenyl)-pyridine)beryllium (Bepp2), 9-(9-Phenylcarbazole-3-yl)-10-(naphthalene-1-yl)anthracene (PCAN), mer-tris(1-phenyl-3-methylimidazolin-2-ylidene-C,C(2)′ iridium(III) (mer-Ir(pmi)3), fac-Tris(1,3-diphenyl-benzimidazolin-2-ylidene-C,C(2)′ iridium(III) (fac-Ir(dpbic)3), bis(3,4,5-trifluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(III) (Ir(tfpd)2pic), tris(2-(4,6-difluorophenyl)pyridine))iridium(III) (Ir(Fppy)3) and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic). 
     In an exemplary aspect, each of the first and second blue EMLs  450  and  470  can include an anthracene derivative as a blue host and a boron derivative as a blue dopant. 
     As illustrated above, the OLED D3 of the present disclosure includes the first emitting part  430  including the red EML  410  and the green EML  420 , the second emitting part  440  including the first blue EML  450  and the third emitting part  460  including the second blue EML  470 . As a result, the OLED D3 emits the white light. 
     In addition, the red EML  410  includes the first compound  412 , which is represented by Formula 1-1, as a red dopant, the second compound  414 , which is represented by Formula 2-1, as a first host or a p-type host, and the third compound  416 , which is represented by Formula 3-1, as a second host or an n-type host. As a result, the OLED D3 has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
       FIG.  7    is a cross-sectional view illustrating an OLED according to a sixth embodiment of the present disclosure. 
     As shown in  FIG.  7   , in the OLED D4, the organic emitting layer  362  includes a first emitting part  530  including a red EML  510  and green EML  520  and a yellow-green EML  525 , a second emitting part  540  including a first blue EML  550  and a third emitting part  560  including a third blue EML  570 . In addition, the organic emitting layer  362  can further include a first CGL  580  between the first and second emitting parts  530  and  540  and a second CGL  590  between the first and third emitting part  530  and  560 . 
     The first electrode  360  is an anode, and the second electrode  364  is a cathode. One of the first and second electrodes  360  and  364  can be a transparent (semitransparent) electrode, and the other one of the first and second electrodes  360  and  364  can be a reflective electrode. 
     The second emitting part  540  is positioned between the first electrode  360  and the first emitting part  530 , and the third emitting part  560  is positioned between the first emitting part  530  and the second electrode  364 . In addition, the second emitting part  540  is positioned between the first electrode  360  and the first CGL  580 , and the third emitting part  560  is positioned between the second CGL  590  and the second electrode  364 . Namely, the second emitting part  540 , the first CGL  580 , the first emitting part  530 , the second CGL  560  and the third emitting part  560  are sequentially stacked on the first electrode  360 . 
     In the first emitting part  530 , the yellow-green EML  525  is positioned between the red EML  510  and the green EML  520 . Namely, the red EML  510 , the yellow-green EML  525  and the green EML  520  are sequentially stacked so that the first emitting part  530  includes an EML having a triple-layered structure. 
     The first emitting part  530  can further include at least one of a first HTL  532  under the red EML  510  and a first ETL  534  over the red EML  510 . 
     The second emitting part  540  can further include at least one of a second HTL  544  under the first blue EML  550  and a second ETL  548  on the first blue EML  550 . In addition, the second emitting part  540  can further include an HIL  542  between the first electrode  360  and the first HTL  544 . 
     The second emitting part  540  can further include at least one of a first EBL between the second HTL  544  and the first blue EML  550  and a first HBL between the first blue EML  550  and the second ETL  548 . 
     The third emitting part  560  can further include at least one of a third HTL  562  under the second blue EML  570  and a third ETL  566  on the second blue EML  570 . In addition, the third emitting part  560  can further include an EIL  568  between the second electrode  364  and the third ETL  566 . 
     The third emitting part  560  can further include at least one of a first EBL between the third HTL  562  and the second blue EML  570  and a first HBL between the second blue EML  570  and the third ETL  566 . 
     For example, the HIL  542  can include at least one of MTDATA, NATA, 4,4′,4″-tris(N-(naphthalene-1-yl)-N-phenyl-amino)triphenylamine 1T-NATA, 2T-NATA, CuPc, TCTA, NPB, HAT-CN, TDAPB, PEDOT/PSS and N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine. 
     Each of the first to third HTLs  532 ,  544  and  564  can include at least one of TPD, NPB, CBP, poly-TPD, TFB, TAPC, DCDPA, N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine, N-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine, and the compound in Formula 4. 
     Each of the first to third ETLs  534 ,  548  and  566  can include at least one of Alq3, PBD, spiro-PBD, Liq, TPBi, BAlq, Bphen, NBphen, BCP, TAZ, NTAZ, TpPyPB, TmPPPyTz, PFNBr, TPQ, and TSPO1. 
     The EIL  568  can include at least one of an alkali halide compound, such as LiF, CsF, NaF, or BaF 2 , and an organo-metallic compound, such as Liq, lithium benzoate, or sodium stearate. 
     The first CGL  580  is positioned between the first and second emitting parts  530  and  540 , and the second CGL  590  is positioned between the first and third emitting parts  530  and  560 . Namely, the first and second emitting parts  530  and  540  is connected to each other by the first CGL  580 , and the first and third emitting parts  530  and  560  is connected to each other by the second CGL  590 . The first CGL  580  can be a P-N junction type CGL of an N-type CGL  582  and a P-type CGL  584 , and the second CGL  590  can be a P-N junction type CGL of an N-type CGL  592  and a P-type CGL  594 . 
     In the first CGL  580 , the N-type CGL  582  is positioned between the first HTL  532  and the second ETL  548 , and the P-type CGL  584  is positioned between the N-type CGL  582  and the first HTL  532 . 
     In the second CGL  590 , the N-type CGL  592  is positioned between the first ETL  534  and the third HTL  562 , and the P-type CGL  594  is positioned between the N-type CGL  592  and the third HTL  562 . 
     Each of the N-type CGL  582  of the first CGL  580  and the N-type CGL  592  of the second CGL  590  can be an organic layer doped with an alkali metal, e.g., Li, Na, K or Cs, and/or an alkali earth metal, e.g., Mg, Sr, Ba or Ra. For example, each of the N-type CGL  582  of the first CGL  580  and the N-type CGL  592  of the second CGL  590  can include an organic material, e.g., 4,7-diphenyl-1,10-phenanthroline (Bphen) or MTDATA, as a host, and the alkali metal and/or the alkali earth metal as a dopant can be doped with a weight % of about 0.01 to 30. 
     Each of the P-type CGL  584  of the first CGL  580  and the P-type CGL  594  of the second CGL  590  can include at least one of an inorganic material, which is selected from the group consisting of tungsten oxide (WOx), molybdenum oxide (MoOx), beryllium oxide (Be2O3), vanadium oxide (V2O5) and their combination, and an organic material, which is selected from the group consisting of NPD, HAT-CN, F4TCNQ, TPD, N,N,N′,N′-tetranaphthyl-benzidine (TNB), TCTA, N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) and their combination. 
     The red EML  510  includes a first compound  512  as a red dopant (e.g., a red emitter), a second compound  514  as a p-type host (e.g., a first host) and a third compound  516  as an n-type host (e.g., a second host). In the red EML  510 , the first compound  512  is represented by Formula 1-1, the second compound  514  is represented by Formula 2-1, and the third compound  516  is represented by Formula 3-1. 
     In the red EML  510 , each of the second and third compounds  514  and  516  can have a weight % being greater than the first compound  512 . For example, in the red EML  510 , the first compound  512  can have a weight % of 1 to 20, e.g., 5 to 15. 
     In addition, in the red EML  510 , a ratio of the weight % between the second compound  514  and the third compound  516  can be 1:3 to 3:1. For example, in the red EML  510 , the second and third compounds  514  and  516  can have the same weight %. 
     In the first emitting part  510 , the green EML  520  includes a green host and a green dopant. The green dopant can be one of a phosphorescent compound, a fluorescent compound and a delayed fluorescent compound. In addition, in the first emitting part  510 , the yellow-green EML  525  includes a yellow-green host and a yellow-green dopant. The yellow-green dopant can be one of a phosphorescent compound, a fluorescent compound and a delayed fluorescent compound. 
     The first blue EML  550  in the second emitting part  540  includes a first blue host and a first blue dopant, and the second blue EML  570  in the third emitting part  560  includes a second blue host and a second blue dopant. 
     For example, each of the first and second blue hosts can be independently selected from the group consisting of mCP, mCP-CN, mCBP, CBP-CN, mCPPO1 Ph-mCP, TSPO1, CzBPCb, UGH-1, UGH-2, UGH-3, SPPO1 and SimCP. 
     For example, each of the first and second blue dopants can be independently selected from the group consisting of perylene, DPAVBi, DPAVB, BDAVBi, spiro-DPVBi, DSB, DSA, TBPe, Bepp2, PCAN, mer-Ir(pmi)3, fac-Ir(dpbic)3, Ir(tfpd)2pic, Ir(Fppy)3 and FIrpic. 
     In an exemplary aspect, each of the first and second blue EMLs  550  and  570  can include an anthracene derivative as a blue host and a boron derivative as a blue dopant. 
     As illustrated above, the OLED D4 of the present disclosure includes the first emitting part  530  including the red EML  510 , the green EML  520  and the yellow-green EML  525 , the second emitting part  540  including the first blue EML  550  and the third emitting part  560  including the second blue EML  570 . As a result, the OLED D4 emits the white light. 
     In addition, the red EML  510  includes the first compound  512 , which is represented by Formula 1-1, as a red dopant, the second compound  514 , which is represented by Formula 2-1, as a first host or a p-type host, and the third compound  516 , which is represented by Formula 3-1, as a second host or an n-type host. As a result, the OLED D4 has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
       FIG.  8    is a cross-sectional view illustrating an OLED according to a seventh embodiment of the present disclosure. 
     As shown in  FIG.  8   , in the OLED D5, the organic emitting layer  362  includes a first emitting part  630  including a red EML  610  and a green EML  620  and a second emitting part  640  including a blue EML  650 . In addition, the organic emitting layer  362  can further include a CGL  660  between the first and second emitting parts  630  and  640 . 
     The first electrode  360  is an anode, and the second electrode  364  is a cathode. One of the first and second electrodes  360  and  364  can be a transparent (semitransparent) electrode, and the other one of the first and second electrodes  360  and  364  can be a reflective electrode. 
     The first emitting part  630  is positioned between the CGL  660  and the second electrode  364 , and the second emitting part  640  is positioned between the CGL  660  and the first electrode  360 . Alternatively, the first emitting part  630  can be positioned between the CGL  660  and the first electrode  360 , and the second emitting part  640  can be positioned between the CGL  660  and the second electrode  364 . 
     In the first emitting part  630 , the green EML  620  is positioned on the red EML  610 . 
     The first emitting part  630  can further include at least one of a first HTL  632  under the red EML  610  and a first ETL  634  over the red EML  610 . When the first emitting part  630  includes the green EML  620 , the first ETL  634  is positioned on the green EML  620 . In addition, the first emitting part  630  can further include an EIL  636  between the first ETL  634  and the second electrode  364 . 
     The second emitting part  640  can further include at least one of a second HTL  644  under the blue EML  650  and a second ETL  646  on the blue EML  650 . In addition, the second emitting part  640  can further include an HIL  642  between the first electrode  360  and the first HTL  644 . 
     For example, the HIL  642  can include at least one of MTDATA, NATA, 4,4′,4″-tris(N-(naphthalene-1-yl)-N-phenyl-amino)triphenylamine 1T-NATA, 2T-NATA, CuPc, TCTA, NPB, HAT-CN, TDAPB, PEDOT/PSS and N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine. 
     Each of the first and second HTLs  632  and  644  can include at least one of TPD, NPB, CBP, poly-TPD, TFB, TAPC, DCDPA, N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine, N-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine, and the compound in Formula 4. 
     Each of the first and second ETLs  634  and  646  can include at least one of Alq3, PBD, spiro-PBD, Liq, TPBi, BAlq, Bphen, NBphen, BCP, TAZ, NTAZ, TpPyPB, TmPPPyTz, PFNBr, TPQ, and TSPO1. 
     The EIL  636  can include at least one of an alkali halide compound, such as LiF, CsF, NaF, or BaF 2 , and an organo-metallic compound, such as Liq, lithium benzoate, or sodium stearate. 
     The CGL  660  is positioned between the first and second emitting parts  630  and  640 . Namely, the first and second emitting parts  630  and  640  is connected to each other by the CGL  660 . 
     The CGL  660  can be a P-N junction type CGL of an N-type CGL  662  and a P-type CGL  664 . 
     In the CGL  660 , the N-type CGL  662  is positioned between the first HTL  632  and the second ETL  646 , and the P-type CGL  664  is positioned between the N-type CGL  662  and the first HTL  632 . 
     The N-type CGL  662  can be an organic layer doped with an alkali metal, e.g., Li, Na, K or Cs, and/or an alkali earth metal, e.g., Mg, Sr, Ba or Ra. For example, the N-type CGL  662  can include an organic material, e.g., 4,7-diphenyl-1,10-phenanthroline (Bphen) or MTDATA, as a host, and the alkali metal and/or the alkali earth metal as a dopant can be doped with a weight % of about 0.01 to 30. 
     The P-type CGL  664  can include at least one of an inorganic material, which is selected from the group consisting of tungsten oxide (WOx), molybdenum oxide (MoOx), beryllium oxide (Be2O3), vanadium oxide (V2O5) and their combination, and an organic material, which is selected from the group consisting of NPD, HAT-CN, F4TCNQ, TPD, N,N,N′,N′-tetranaphthyl-benzidine (TNB), TCTA, N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) and their combination. 
     The red EML  610  includes a first compound  612  as a red dopant (e.g., a red emitter), a second compound  614  as a p-type host (e.g., a first host) and a third compound  616  as an n-type host (e.g., a second host). In the red EML  610 , the first compound  612  is represented by Formula 1-1, the second compound  614  is represented by Formula 2-1, and the third compound  616  is represented by Formula 3-1. 
     In the red EML  610 , each of the second and third compounds  614  and  616  can have a weight % being greater than the first compound  612 . For example, in the red EML  610 , the first compound  612  can have a weight % of 1 to 20, e.g., 5 to 15. 
     In addition, in the red EML  610 , a ratio of the weight % between the second compound  614  and the third compound  616  can be 1:3 to 3:1. For example, in the red EML  610 , the second and third compounds  614  and  616  can have the same weight %. 
     In the first emitting part  610 , the green EML  620  includes a green host and a green dopant. The green dopant can be one of a phosphorescent compound, a fluorescent compound and a delayed fluorescent compound. 
     The blue EML  650  in the second emitting part  640  includes a blue host and a blue dopant. 
     For example, the blue host can be selected from the group consisting of mCP, mCP-CN, mCBP, CBP-CN, mCPPO1 Ph-mCP, TSPO1, CzBPCb, UGH-1, UGH-2, UGH-3, SPPO1 and SimCP, a and the blue dopant can be selected from the group consisting of perylene, DPAVBi, DPAVB, BDAVBi, spiro-DPVBi, DSB, DSA, TBPe, Bepp2, PCAN, mer-Ir(pmi)3, fac-Ir(dpbic)3, Ir(tfpd)2pic, Ir(Fppy)3 and FIrpic. 
     In an exemplary aspect, the blue EML  650  can include an anthracene derivative as a blue host and a boron derivative as a blue dopant. 
     As illustrated above, the OLED D5 of the present disclosure includes the first emitting part  630  including the red EML  610  and the green EML  620  and the second emitting part  640  including the blue EML  650 . As a result, the OLED D5 emits the white light. 
     In addition, the red EML  610  includes the first compound  612 , which is represented by Formula 1-1, as a red dopant, the second compound  614 , which is represented by Formula 2-1, as a first host or a p-type host, and the third compound  616 , which is represented by Formula 3-1, as a second host or an n-type host. As a result, the OLED D5 has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     [OLED] 
     The anode (ITO), the HIL (HATCN (the compound in Formula 5), 100 Å), the HTL (the compound in Formula 4, 700 Å), the EML (host and dopant (10 wt. %), 300 Å), the ETL (Alq3, 300 Å), the EIL (LiF, 10 Å) and the cathode (Al, 1000 Å) was sequentially deposited. An encapsulation film is formed by using an UV curable epoxy and a moisture getter to form the OLED. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     1. Comparative Example 1 (Ref1) 
     The compound RD1 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     2. Examples 
     (1) Examples 1 to 4 (Ex1 to Ex4) 
     The compound RD1 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 5 to 8 (Ex5 to Ex8) 
     The compound RD1 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 9 to 12 (Ex9 to Ex12) 
     The compound RD1 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 13 to 16 (Ex13 to Ex16) 
     The compound RD1 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 1 and Examples 1 to 16 are measured and listed in Table 1. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref1 
                 RD1 
                 CBP 
                 4.28 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex1 
                 RD1 
                 RHH-2 
                 REH-1 
                 4.21 
                 127 
                 135 
               
               
                 Ex2 
                 RD1 
                 RHH-2 
                 REH-11 
                 4.19 
                 125 
                 134 
               
               
                 Ex3 
                 RD1 
                 RHH-2 
                 REH-16 
                 4.24 
                 117 
                 120 
               
               
                 Ex4 
                 RD1 
                 RHH-2 
                 REH-30 
                 4.22 
                 114 
                 117 
               
               
                 Ex5 
                 RD1 
                 RHH-8 
                 REH-1 
                 4.16 
                 131 
                 138 
               
               
                 Ex6 
                 RD1 
                 RHH-8 
                 REH-11 
                 4.16 
                 126 
                 135 
               
               
                 Ex7 
                 RD1 
                 RHH-8 
                 REH-16 
                 4.18 
                 121 
                 126 
               
               
                 Ex8 
                 RD1 
                 RHH-8 
                 REH-30 
                 4.18 
                 118 
                 121 
               
               
                 Ex9 
                 RD1 
                 RHH-20 
                 REH-1 
                 4.14 
                 127 
                 134 
               
               
                 Ex10 
                 RD1 
                 RHH-20 
                 REH-11 
                 4.12 
                 125 
                 130 
               
               
                 Ex11 
                 RD1 
                 RHH-20 
                 REH-16 
                 4.17 
                 114 
                 126 
               
               
                 Ex12 
                 RD1 
                 RHH-20 
                 REH-30 
                 4.16 
                 111 
                 120 
               
               
                 Ex13 
                 RD1 
                 RHH-27 
                 REH-1 
                 4.17 
                 115 
                 130 
               
               
                 Ex14 
                 RD1 
                 RHH-27 
                 REH-11 
                 4.17 
                 113 
                 126 
               
               
                 Ex15 
                 RD1 
                 RHH-27 
                 REH-16 
                 4.19 
                 107 
                 116 
               
               
                 Ex16 
                 RD1 
                 RHH-27 
                 REH-30 
                 4.20 
                 105 
                 115 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, in comparison to the OLED of Ref1, in which the red EML includes the compound RD1 as a dopant and CBP as a host, the OLED of Ex1 to Ex16, in which the red EML includes the compound RD1 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 1 to 12, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD1 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 1, 2, 5, 6, 9, 10, 13 and 14, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD1 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     3. Comparative Example 2 (Ref2) 
     The compound RD2 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     4. Examples 
     (1) Examples 17 to 20 (Ex17 to Ex20) 
     The compound RD2 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 21 to 24 (Ex21 to Ex24) 
     The compound RD2 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 25 to 28 (Ex25 to Ex28) 
     The compound RD2 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 29 to 32 (Ex29 to Ex32) 
     The compound RD2 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 2 and Examples 17 to 32 are measured and listed in Table 2. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref2 
                 RD2 
                 CBP 
                 4.30 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex17 
                 RD2 
                 RHH-2 
                 REH-1 
                 4.21 
                 125 
                 134 
               
               
                 Ex18 
                 RD2 
                 RHH-2 
                 REH-11 
                 4.22 
                 123 
                 128 
               
               
                 Ex19 
                 RD2 
                 RHH-2 
                 REH-16 
                 4.24 
                 116 
                 122 
               
               
                 Ex20 
                 RD2 
                 RHH-2 
                 REH-30 
                 4.24 
                 112 
                 119 
               
               
                 Ex21 
                 RD2 
                 RHH-8 
                 REH-1 
                 4.18 
                 127 
                 135 
               
               
                 Ex22 
                 RD2 
                 RHH-8 
                 REH-11 
                 4.19 
                 121 
                 130 
               
               
                 Ex23 
                 RD2 
                 RHH-8 
                 REH-16 
                 4.22 
                 115 
                 125 
               
               
                 Ex24 
                 RD2 
                 RHH-8 
                 REH-30 
                 4.23 
                 111 
                 118 
               
               
                 Ex25 
                 RD2 
                 RHH-20 
                 REH-1 
                 4.17 
                 125 
                 133 
               
               
                 Ex26 
                 RD2 
                 RHH-20 
                 REH-11 
                 4.18 
                 121 
                 127 
               
               
                 Ex27 
                 RD2 
                 RHH-20 
                 REH-16 
                 4.21 
                 111 
                 123 
               
               
                 Ex28 
                 RD2 
                 RHH-20 
                 REH-30 
                 4.24 
                 108 
                 119 
               
               
                 Ex29 
                 RD2 
                 RHH-27 
                 REH-1 
                 4.20 
                 110 
                 128 
               
               
                 Ex30 
                 RD2 
                 RHH-27 
                 REH-11 
                 4.21 
                 109 
                 121 
               
               
                 Ex31 
                 RD2 
                 RHH-27 
                 REH-16 
                 4.24 
                 105 
                 114 
               
               
                 Ex32 
                 RD2 
                 RHH-27 
                 REH-30 
                 4.25 
                 105 
                 115 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, in comparison to the OLED of Ref2, in which the red EML includes the compound RD2 as a dopant and CBP as a host, the OLED of Ex17 to Ex32, in which the red EML includes the compound RD2 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 17 to 28, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD2 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 17, 18, 21, 22, 25, 26, 29 and 30, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD2 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     5. Comparative Example 3 (Ref3) 
     The compound RD3 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     6. Examples 
     (1) Examples 33 to 36 (Ex33 to Ex36) 
     The compound RD3 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds RHH-2, RHH-8, RHH-20 or RHH-27 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 37 to 40 (Ex37 to Ex40) 
     The compound RD3 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds RHH-2, RHH-8, RHH-20 or RHH-27 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 41 to 44 (Ex41 to Ex44) 
     The compound RD3 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds RHH-2, RHH-8, RHH-20 or RHH-27 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 45 to 48 (Ex45 to Ex48) 
     The compound RD3 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds RHH-2, RHH-8, RHH-20 or RHH-27 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 3 and Examples 33 to 48 are measured and listed in Table 3. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref3 
                 RD3 
                 CBP 
                 4.30 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex33 
                 RD3 
                 RHH-2 
                 REH-1 
                 4.22 
                 124 
                 132 
               
               
                 Ex34 
                 RD3 
                 RHH-2 
                 REH-11 
                 4.22 
                 122 
                 127 
               
               
                 Ex35 
                 RD3 
                 RHH-2 
                 REH-16 
                 4.24 
                 119 
                 118 
               
               
                 Ex36 
                 RD3 
                 RHH-2 
                 REH-30 
                 4.26 
                 115 
                 117 
               
               
                 Ex37 
                 RD3 
                 RHH-8 
                 REH-1 
                 4.18 
                 127 
                 134 
               
               
                 Ex38 
                 RD3 
                 RHH-8 
                 REH-11 
                 4.19 
                 124 
                 129 
               
               
                 Ex39 
                 RD3 
                 RHH-8 
                 REH-16 
                 4.23 
                 119 
                 126 
               
               
                 Ex40 
                 RD3 
                 RHH-8 
                 REH-30 
                 4.24 
                 117 
                 121 
               
               
                 Ex41 
                 RD3 
                 RHH-20 
                 REH-1 
                 4.17 
                 122 
                 131 
               
               
                 Ex42 
                 RD3 
                 RHH-20 
                 REH-11 
                 4.18 
                 120 
                 125 
               
               
                 Ex43 
                 RD3 
                 RHH-20 
                 REH-16 
                 4.21 
                 118 
                 121 
               
               
                 Ex44 
                 RD3 
                 RHH-20 
                 REH-30 
                 4.22 
                 114 
                 118 
               
               
                 Ex45 
                 RD3 
                 RHH-27 
                 REH-1 
                 4.19 
                 117 
                 126 
               
               
                 Ex46 
                 RD3 
                 RHH-27 
                 REH-11 
                 4.20 
                 115 
                 122 
               
               
                 Ex47 
                 RD3 
                 RHH-27 
                 REH-16 
                 4.24 
                 110 
                 114 
               
               
                 Ex48 
                 RD3 
                 RHH-27 
                 REH-30 
                 4.25 
                 107 
                 115 
               
               
                   
               
            
           
         
       
     
     As shown in Table 3, in comparison to the OLED of Ref3, in which the red EML includes the compound RD3 as a dopant and CBP as a host, the OLED of Ex33 to Ex48, in which the red EML includes the compound RD3 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 33 to 44, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD3 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 33, 34, 37, 38, 41, 42, 45 and 46, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD3 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     7. Comparative Example 4 (Ref4) 
     The compound RD4 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     8. Examples 
     (1) Examples 49 to 52 (Ex49 to Ex52) 
     The compound RD4 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 53 to 56 (Ex53 to Ex56) 
     The compound RD4 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 57 to 60 (Ex57 to Ex60) 
     The compound RD4 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 and REH-28 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 61 to 64 (Ex61 to Ex64) 
     The compound RD4 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 4 and Examples 49 to 64 are measured and listed in Table 4. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref4 
                 RD4 
                 CBP 
                 4.31 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex49 
                 RD4 
                 RHH-2 
                 REH-1 
                 4.23 
                 122 
                 128 
               
               
                 Ex50 
                 RD4 
                 RHH-2 
                 REH-11 
                 4.22 
                 120 
                 122 
               
               
                 Ex51 
                 RD4 
                 RHH-2 
                 REH-16 
                 4.24 
                 118 
                 117 
               
               
                 Ex52 
                 RD4 
                 RHH-2 
                 REH-30 
                 4.23 
                 112 
                 112 
               
               
                 Ex53 
                 RD4 
                 RHH-8 
                 REH-1 
                 4.19 
                 125 
                 133 
               
               
                 Ex54 
                 RD4 
                 RHH-8 
                 REH-11 
                 4.20 
                 121 
                 126 
               
               
                 Ex55 
                 RD4 
                 RHH-8 
                 REH-16 
                 4.22 
                 119 
                 122 
               
               
                 Ex56 
                 RD4 
                 RHH-8 
                 REH-30 
                 4.24 
                 116 
                 119 
               
               
                 Ex57 
                 RD4 
                 RHH-20 
                 REH-1 
                 4.18 
                 123 
                 131 
               
               
                 Ex58 
                 RD4 
                 RHH-20 
                 REH-11 
                 4.18 
                 119 
                 128 
               
               
                 Ex59 
                 RD4 
                 RHH-20 
                 REH-16 
                 4.22 
                 115 
                 117 
               
               
                 Ex60 
                 RD4 
                 RHH-20 
                 REH-30 
                 4.23 
                 112 
                 116 
               
               
                 Ex61 
                 RD4 
                 RHH-27 
                 REH-1 
                 4.23 
                 118 
                 127 
               
               
                 Ex62 
                 RD4 
                 RHH-27 
                 REH-11 
                 4.24 
                 115 
                 124 
               
               
                 Ex63 
                 RD4 
                 RHH-27 
                 REH-16 
                 4.25 
                 110 
                 117 
               
               
                 Ex64 
                 RD4 
                 RHH-27 
                 REH-30 
                 4.28 
                 111 
                 116 
               
               
                   
               
            
           
         
       
     
     As shown in Table 4, in comparison to the OLED of Ref4, in which the red EML includes the compound RD4 as a dopant and CBP as a host, the OLED of Ex49 to Ex64, in which the red EML includes the compound RD4 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 49 to 60, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD4 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 49, 50, 53, 54, 57, 58, 61 and 62, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD4 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     9. Comparative Example 5 (Ref5) 
     The compound RD5 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     10. Examples 
     (1) Examples 65 and 68 (Ex65 and Ex68) 
     The compound RD5 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 69 and 72 (Ex69 and Ex72) 
     The compound RD5 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 73 and 76 (Ex73 and Ex76) 
     The compound RD5 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 77 and 80 (Ex77 and Ex80) 
     The compound RD5 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 5 and Examples 65 to 80 are measured and listed in Table 5. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref5 
                 RD5 
                 CBP 
                 4.28 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex65 
                 RD5 
                 RHH-2 
                 REH-1 
                 4.21 
                 126 
                 132 
               
               
                 Ex66 
                 RD5 
                 RHH-2 
                 REH-11 
                 4.19 
                 125 
                 127 
               
               
                 Ex67 
                 RD5 
                 RHH-2 
                 REH-16 
                 4.23 
                 117 
                 118 
               
               
                 Ex68 
                 RD5 
                 RHH-2 
                 REH-30 
                 4.22 
                 115 
                 113 
               
               
                 Ex69 
                 RD5 
                 RHH-8 
                 REH-1 
                 4.16 
                 129 
                 138 
               
               
                 Ex70 
                 RD5 
                 RHH-8 
                 REH-11 
                 4.17 
                 123 
                 134 
               
               
                 Ex71 
                 RD5 
                 RHH-8 
                 REH-16 
                 4.18 
                 117 
                 121 
               
               
                 Ex72 
                 RD5 
                 RHH-8 
                 REH-30 
                 4.18 
                 115 
                 118 
               
               
                 Ex73 
                 RD5 
                 RHH-20 
                 REH-1 
                 4.15 
                 125 
                 134 
               
               
                 Ex74 
                 RD5 
                 RHH-20 
                 REH-11 
                 4.15 
                 123 
                 129 
               
               
                 Ex75 
                 RD5 
                 RHH-20 
                 REH-16 
                 4.18 
                 111 
                 123 
               
               
                 Ex76 
                 RD5 
                 RHH-20 
                 REH-30 
                 4.19 
                 112 
                 117 
               
               
                 Ex77 
                 RD5 
                 RHH-27 
                 REH-1 
                 4.19 
                 115 
                 126 
               
               
                 Ex78 
                 RD5 
                 RHH-27 
                 REH-11 
                 4.20 
                 113 
                 122 
               
               
                 Ex79 
                 RD5 
                 RHH-27 
                 REH-16 
                 4.23 
                 108 
                 115 
               
               
                 Ex80 
                 RD5 
                 RHH-27 
                 REH-30 
                 4.22 
                 108 
                 112 
               
               
                   
               
            
           
         
       
     
     As shown in Table 5, in comparison to the OLED of Ref5, in which the red EML includes the compound RD5 as a dopant and CBP as a host, the OLED of Ex65 to Ex80, in which the red EML includes the compound RD5 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 65 to 76, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD5 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 65, 66, 69, 70, 73, 74, 77 and 78, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD5 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     11. Comparative Example 6 (Ref6) 
     The compound RD6 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     12. Examples 
     (1) Examples 81 and 84 (Ex81 and Ex84) 
     The compound RD6 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 85 and 88 (Ex85 and Ex88) 
     The compound RD6 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 89 and 92 (Ex89 and Ex92) 
     The compound RD6 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 93 and 96 (Ex93 and Ex96) 
     The compound RD6 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 6 and Examples 81 to 96 are measured and listed in Table 6. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref6 
                 RD6 
                 CBP 
                 4.30 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex81 
                 RD6 
                 RHH-2 
                 REH-1 
                 4.23 
                 125 
                 133 
               
               
                 Ex82 
                 RD6 
                 RHH-2 
                 REH-11 
                 4.22 
                 123 
                 128 
               
               
                 Ex83 
                 RD6 
                 RHH-2 
                 REH-16 
                 4.24 
                 116 
                 121 
               
               
                 Ex84 
                 RD6 
                 RHH-2 
                 REH-30 
                 4.23 
                 112 
                 117 
               
               
                 Ex85 
                 RD6 
                 RHH-8 
                 REH-1 
                 4.18 
                 127 
                 134 
               
               
                 Ex86 
                 RD6 
                 RHH-8 
                 REH-11 
                 4.18 
                 121 
                 129 
               
               
                 Ex87 
                 RD6 
                 RHH-8 
                 REH-16 
                 4.22 
                 115 
                 120 
               
               
                 Ex88 
                 RD6 
                 RHH-8 
                 REH-30 
                 4.21 
                 111 
                 116 
               
               
                 Ex89 
                 RD6 
                 RHH-20 
                 REH-1 
                 4.17 
                 125 
                 130 
               
               
                 Ex90 
                 RD6 
                 RHH-20 
                 REH-11 
                 4.16 
                 121 
                 125 
               
               
                 Ex91 
                 RD6 
                 RHH-20 
                 REH-16 
                 4.21 
                 111 
                 121 
               
               
                 Ex92 
                 RD6 
                 RHH-20 
                 REH-30 
                 4.22 
                 108 
                 117 
               
               
                 Ex93 
                 RD6 
                 RHH-27 
                 REH-1 
                 4.22 
                 110 
                 125 
               
               
                 Ex94 
                 RD6 
                 RHH-27 
                 REH-11 
                 4.20 
                 109 
                 119 
               
               
                 Ex95 
                 RD6 
                 RHH-27 
                 REH-16 
                 4.24 
                 105 
                 108 
               
               
                 Ex96 
                 RD6 
                 RHH-27 
                 REH-30 
                 4.23 
                 105 
                 110 
               
               
                   
               
            
           
         
       
     
     As shown in Table 6, in comparison to the OLED of Ref6, in which the red EML includes the compound RD6 as a dopant and CBP as a host, the OLED of Ex81 to Ex96, in which the red EML includes the compound RD6 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 81 to 92, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD6 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 81, 82, 85, 86, 89, 90, 93 and 94, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD6 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     13. Comparative Example 7 (Ref7) 
     The compound RD7 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     14. Examples 
     (1) Examples 97 and 100 (Ex97 and Ex100) 
     The compound RD7 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 101 and 104 (Ex101 and Ex104) 
     The compound RD7 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 105 and 108 (Ex105 and Ex108) 
     The compound RD7 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 109 and 112 (Ex109 and Ex112) 
     The compound RD7 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 7 and Examples 97 to 112 are measured and listed in Table 7. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 7 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref7 
                 RD7 
                 CBP 
                 4.31 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex97 
                 RD7 
                 RHH-2 
                 REH-1 
                 4.22 
                 123 
                 131 
               
               
                 Ex98 
                 RD7 
                 RHH-2 
                 REH-11 
                 4.22 
                 121 
                 126 
               
               
                 Ex99 
                 RD7 
                 RHH-2 
                 REH-16 
                 4.25 
                 117 
                 117 
               
               
                 Ex100 
                 RD7 
                 RHH-2 
                 REH-30 
                 4.26 
                 114 
                 115 
               
               
                 Ex101 
                 RD7 
                 RHH-8 
                 REH-1 
                 4.19 
                 126 
                 132 
               
               
                 Ex102 
                 RD7 
                 RHH-8 
                 REH-11 
                 4.20 
                 123 
                 128 
               
               
                 Ex103 
                 RD7 
                 RHH-8 
                 REH-16 
                 4.23 
                 119 
                 123 
               
               
                 Ex104 
                 RD7 
                 RHH-8 
                 REH-30 
                 4.24 
                 118 
                 119 
               
               
                 Ex105 
                 RD7 
                 RHH-20 
                 REH-1 
                 4.18 
                 123 
                 130 
               
               
                 Ex106 
                 RD7 
                 RHH-20 
                 REH-11 
                 4.19 
                 120 
                 123 
               
               
                 Ex107 
                 RD7 
                 RHH-20 
                 REH-16 
                 4.22 
                 118 
                 120 
               
               
                 Ex108 
                 RD7 
                 RHH-20 
                 REH-30 
                 4.24 
                 115 
                 116 
               
               
                 Ex109 
                 RD7 
                 RHH-27 
                 REH-1 
                 4.20 
                 116 
                 124 
               
               
                 Ex110 
                 RD7 
                 RHH-27 
                 REH-11 
                 4.21 
                 115 
                 120 
               
               
                 Ex111 
                 RD7 
                 RHH-27 
                 REH-16 
                 4.25 
                 109 
                 112 
               
               
                 Ex112 
                 RD7 
                 RHH-27 
                 REH-30 
                 4.27 
                 105 
                 110 
               
               
                   
               
            
           
         
       
     
     As shown in Table 7, in comparison to the OLED of Ref7, in which the red EML includes the compound RD7 as a dopant and CBP as a host, the OLED of Ex97 to Ex112, in which the red EML includes the compound RD7 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 97 to 108, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD7 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 97, 98, 101, 102, 105, 106, 109 and 110, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD7 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     15. Comparative Example 8 (Ref8) 
     The compound RD8 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     16. Examples 
     (1) Examples 113 and 116 (Ex113 and Ex116) 
     The compound RD8 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 117 and 120 (Ex117 and Ex120) 
     The compound RD8 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 121 and 124 (Ex121 and Ex124) 
     The compound RD8 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 125 and 128 (Ex125 and Ex128) 
     The compound RD8 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 or REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example Band Examples 113 to 128 are measured and listed in Table 8. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 8 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref8 
                 RD8 
                 CBP 
                 4.32 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex113 
                 RD8 
                 RHH-2 
                 REH-1 
                 4.25 
                 120 
                 126 
               
               
                 Ex114 
                 RD8 
                 RHH-2 
                 REH-11 
                 4.23 
                 119 
                 121 
               
               
                 Ex115 
                 RD8 
                 RHH-2 
                 REH-16 
                 4.26 
                 116 
                 115 
               
               
                 Ex116 
                 RD8 
                 RHH-2 
                 REH-30 
                 4.25 
                 110 
                 110 
               
               
                 Ex117 
                 RD8 
                 RHH-8 
                 REH-1 
                 4.20 
                 125 
                 130 
               
               
                 Ex118 
                 RD8 
                 RHH-8 
                 REH-11 
                 4.22 
                 119 
                 124 
               
               
                 Ex119 
                 RD8 
                 RHH-8 
                 REH-16 
                 4.24 
                 119 
                 119 
               
               
                 Ex120 
                 RD8 
                 RHH-8 
                 REH-30 
                 4.25 
                 113 
                 116 
               
               
                 Ex121 
                 RD8 
                 RHH-20 
                 REH-1 
                 4.19 
                 121 
                 127 
               
               
                 Ex122 
                 RD8 
                 RHH-20 
                 REH-11 
                 4.19 
                 118 
                 121 
               
               
                 Ex123 
                 RD8 
                 RHH-20 
                 REH-16 
                 4.23 
                 112 
                 117 
               
               
                 Ex124 
                 RD8 
                 RHH-20 
                 REH-30 
                 4.24 
                 108 
                 114 
               
               
                 Ex125 
                 RD8 
                 RHH-27 
                 REH-1 
                 4.23 
                 115 
                 123 
               
               
                 Ex126 
                 RD8 
                 RHH-27 
                 REH-11 
                 4.25 
                 110 
                 116 
               
               
                 Ex127 
                 RD8 
                 RHH-27 
                 REH-16 
                 4.25 
                 109 
                 109 
               
               
                 Ex128 
                 RD8 
                 RHH-27 
                 REH-30 
                 4.28 
                 107 
                 110 
               
               
                   
               
            
           
         
       
     
     As shown in Table 8, in comparison to the OLED of Ref8, in which the red EML includes the compound RD8 as a dopant and CBP as a host, the OLED of Ex113 to Ex128, in which the red EML includes the compound RD8 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 113 to 124, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD8 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 113, 114, 117, 118, 121, 122, 125 and 126, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD8 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     17. Comparative Example 9 (Ref9) 
     The compound RD9 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     18. Examples 
     (1) Examples 129 and 131 (Ex129 and Ex131) 
     The compound RD9 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 132 and 134 (Ex132 and Ex134) 
     The compound RD9 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 135 and 137 (Ex135 and Ex137) 
     The compound RD9 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 9 and Examples 129 to 137 are measured and listed in Table 9. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 9 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref9 
                 RD9 
                 CBP 
                 4.29 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex129 
                 RD9 
                 RHH-2 
                 REH-1 
                 4.20 
                 118 
                 120 
               
               
                 Ex130 
                 RD9 
                 RHH-2 
                 REH-11 
                 4.18 
                 117 
                 115 
               
               
                 Ex131 
                 RD9 
                 RHH-2 
                 REH-16 
                 4.21 
                 115 
                 109 
               
               
                 Ex132 
                 RD9 
                 RHH-8 
                 REH-1 
                 4.18 
                 121 
                 121 
               
               
                 Ex133 
                 RD9 
                 RHH-8 
                 REH-11 
                 4.16 
                 115 
                 120 
               
               
                 Ex134 
                 RD9 
                 RHH-8 
                 REH-16 
                 4.20 
                 114 
                 116 
               
               
                 Ex135 
                 RD9 
                 RHH-20 
                 REH-1 
                 4.15 
                 118 
                 119 
               
               
                 Ex136 
                 RD9 
                 RHH-20 
                 REH-11 
                 4.13 
                 115 
                 116 
               
               
                 Ex137 
                 RD9 
                 RHH-20 
                 REH-16 
                 4.17 
                 113 
                 114 
               
               
                   
               
            
           
         
       
     
     As shown in Table 9, in comparison to the OLED of Ref9, in which the red EML includes the compound RD9 as a dopant and CBP as a host, the OLED of Ex129 to Ex137, in which the red EML includes the compound RD9 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 129, 130, 132, 133, 135 and 136, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD9 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     19. Comparative Example 10 (Ref10) 
     The compound RD10 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     20. Examples 
     (1) Examples 138 and 140 (Ex138 and Ex140) 
     The compound RD10 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 141 and 143 (Ex141 and Ex143) 
     The compound RD10 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 144 and 146 (Ex144 and Ex146) 
     The compound RD10 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 10 and Examples 138 to 146 are measured and listed in Table 10. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 10 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref10 
                 RD10 
                 CBP 
                 4.30 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex138 
                 RD10 
                 RHH-2 
                 REH-1 
                 4.21 
                 117 
                 120 
               
               
                 Ex139 
                 RD10 
                 RHH-2 
                 REH-11 
                 4.20 
                 117 
                 116 
               
               
                 Ex140 
                 RD10 
                 RHH-2 
                 REH-16 
                 4.22 
                 114 
                 110 
               
               
                 Ex141 
                 RD10 
                 RHH-8 
                 REH-1 
                 4.19 
                 120 
                 120 
               
               
                 Ex142 
                 RD10 
                 RHH-8 
                 REH-11 
                 4.17 
                 116 
                 118 
               
               
                 Ex143 
                 RD10 
                 RHH-8 
                 REH-16 
                 4.20 
                 115 
                 115 
               
               
                 Ex144 
                 RD10 
                 RHH-20 
                 REH-1 
                 4.17 
                 117 
                 118 
               
               
                 Ex145 
                 RD10 
                 RHH-20 
                 REH-11 
                 4.15 
                 114 
                 115 
               
               
                 Ex146 
                 RD10 
                 RHH-20 
                 REH-16 
                 4.18 
                 111 
                 113 
               
               
                   
               
            
           
         
       
     
     As shown in Table 10, in comparison to the OLED of Ref10, in which the red EML includes the compound RD10 as a dopant and CBP as a host, the OLED of Ex138 to Ex146, in which the red EML includes the compound RD10 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 138, 139, 141, 142, 144 and 145, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD10 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     21. Comparative Example 11 (Ref1l) 
     The compound RD11 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     22. Examples 
     (1) Examples 147 and 149 (Ex147 and Ex149) 
     The compound RD11 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 150 and 152 (Ex150 and Ex152) 
     The compound RD11 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 153 and 155 (Ex153 and Ex155) 
     The compound RD11 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 1 land Examples 147 to 155 are measured and listed in Table 11. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 11 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref11 
                 RD11 
                 CBP 
                 4.31 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex147 
                 RD11 
                 RHH-2 
                 REH-1 
                 4.23 
                 117 
                 119 
               
               
                 Ex148 
                 RD11 
                 RHH-2 
                 REH-11 
                 4.21 
                 118 
                 114 
               
               
                 Ex149 
                 RD11 
                 RHH-2 
                 REH-16 
                 4.23 
                 114 
                 110 
               
               
                 Ex150 
                 RD11 
                 RHH-8 
                 REH-1 
                 4.20 
                 119 
                 121 
               
               
                 Ex151 
                 RD11 
                 RHH-8 
                 REH-11 
                 4.19 
                 117 
                 118 
               
               
                 Ex152 
                 RD11 
                 RHH-8 
                 REH-16 
                 4.21 
                 113 
                 114 
               
               
                 Ex153 
                 RD11 
                 RHH-20 
                 REH-1 
                 4.18 
                 115 
                 116 
               
               
                 Ex154 
                 RD11 
                 RHH-20 
                 REH-11 
                 4.17 
                 113 
                 112 
               
               
                 Ex155 
                 RD11 
                 RHH-20 
                 REH-16 
                 4.20 
                 112 
                 110 
               
               
                   
               
            
           
         
       
     
     As shown in Table 11, in comparison to the OLED of Ref11, in which the red EML includes the compound RD11 as a dopant and CBP as a host, the OLED of Ex147 to Ex155, in which the red EML includes the compound RD11 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 147, 148, 150, 151, 153 and 154, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD11 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     23. Comparative Example 12 (Ref12) 
     The compound RD12 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     24. Examples 
     (1) Examples 156 and 158 (Ex156 and Ex158) 
     The compound RD12 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 159 and 161 (Ex159 and Ex161) 
     The compound RD12 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 162 and 164 (Ex162 and Ex164) 
     The compound RD12 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 12 and Examples 156 to 164 are measured and listed in Table 12. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 12 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref12 
                 RD12 
                 CBP 
                 4.31 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex156 
                 RD12 
                 RHH-2 
                 REH-1 
                 4.24 
                 116 
                 119 
               
               
                 Ex157 
                 RD12 
                 RHH-2 
                 REH-11 
                 4.22 
                 118 
                 115 
               
               
                 Ex158 
                 RD12 
                 RHH-2 
                 REH-16 
                 4.23 
                 115 
                 111 
               
               
                 Ex159 
                 RD12 
                 RHH-8 
                 REH-1 
                 4.21 
                 117 
                 123 
               
               
                 Ex160 
                 RD12 
                 RHH-8 
                 REH-11 
                 4.20 
                 115 
                 119 
               
               
                 Ex161 
                 RD12 
                 RHH-8 
                 REH-16 
                 4.22 
                 111 
                 115 
               
               
                 Ex162 
                 RD12 
                 RHH-20 
                 REH-1 
                 4.19 
                 114 
                 113 
               
               
                 Ex163 
                 RD12 
                 RHH-20 
                 REH-11 
                 4.18 
                 112 
                 110 
               
               
                 Ex164 
                 RD12 
                 RHH-20 
                 REH-16 
                 4.21 
                 110 
                 108 
               
               
                   
               
            
           
         
       
     
     As shown in Table 12, in comparison to the OLED of Ref12, in which the red EML includes the compound RD12 as a dopant and CBP as a host, the OLED of Ex156 to Ex164, in which the red EML includes the compound RD12 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 156, 147, 159, 160, 162 and 163, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD12 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     25. Comparative Example 13 (Ref13) 
     The compound RD13 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     26. Examples 
     (1) Examples 165 and 167 (Ex165 and Ex167) 
     The compound RD13 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 168 and 170 (Ex168 and Ex170) 
     The compound RD13 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 171 and 173 (Ex171 and Ex173) 
     The compound RD13 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 13 and Examples 165 to 173 are measured and listed in Table 13. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 13 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref13 
                 RD13 
                 CBP 
                 4.26 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex165 
                 RD13 
                 RHH-2 
                 REH-1 
                 4.18 
                 115 
                 116 
               
               
                 Ex166 
                 RD13 
                 RHH-2 
                 REH-11 
                 4.14 
                 114 
                 114 
               
               
                 Ex167 
                 RD13 
                 RHH-2 
                 REH-16 
                 4.17 
                 113 
                 109 
               
               
                 Ex168 
                 RD13 
                 RHH-8 
                 REH-1 
                 4.15 
                 116 
                 118 
               
               
                 Ex169 
                 RD13 
                 RHH-8 
                 REH-11 
                 4.14 
                 115 
                 117 
               
               
                 Ex170 
                 RD13 
                 RHH-8 
                 REH-16 
                 4.19 
                 113 
                 115 
               
               
                 Ex171 
                 RD13 
                 RHH-20 
                 REH-1 
                 4.14 
                 115 
                 116 
               
               
                 Ex172 
                 RD13 
                 RHH-20 
                 REH-11 
                 4.12 
                 112 
                 113 
               
               
                 Ex173 
                 RD13 
                 RHH-20 
                 REH-16 
                 4.15 
                 111 
                 111 
               
               
                   
               
            
           
         
       
     
     As shown in Table 13, in comparison to the OLED of Ref13, in which the red EML includes the compound RD13 as a dopant and CBP as a host, the OLED of Ex165 to Ex173, in which the red EML includes the compound RD13 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 165, 166, 168, 169, 171 and 172, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD13 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     27. Comparative Example 14 (Ref14) 
     The compound RD14 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     28. Examples 
     (1) Examples 174 and 176 (Ex174 and Ex176) 
     The compound RD14 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 177 and 179 (Ex177 and Ex179) 
     The compound RD14 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 180 and 182 (Ex180 and Ex182) 
     The compound RD14 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 14 and Examples 174 to 182 are measured and listed in Table 14. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 14 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref14 
                 RD14 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex174 
                 RD14 
                 RHH-2 
                 REH-1 
                 4.19 
                 114 
                 115 
               
               
                 Ex175 
                 RD14 
                 RHH-2 
                 REH-11 
                 4.15 
                 113 
                 111 
               
               
                 Ex176 
                 RD14 
                 RHH-2 
                 REH-16 
                 4.17 
                 112 
                 108 
               
               
                 Ex177 
                 RD14 
                 RHH-8 
                 REH-1 
                 4.15 
                 115 
                 116 
               
               
                 Ex178 
                 RD14 
                 RHH-8 
                 REH-11 
                 4.15 
                 114 
                 115 
               
               
                 Ex179 
                 RD14 
                 RHH-8 
                 REH-16 
                 4.18 
                 112 
                 110 
               
               
                 Ex180 
                 RD14 
                 RHH-20 
                 REH-1 
                 4.16 
                 114 
                 113 
               
               
                 Ex181 
                 RD14 
                 RHH-20 
                 REH-11 
                 4.14 
                 111 
                 107 
               
               
                 Ex182 
                 RD14 
                 RHH-20 
                 REH-16 
                 4.16 
                 109 
                 105 
               
               
                   
               
            
           
         
       
     
     As shown in Table 14, in comparison to the OLED of Ref14, in which the red EML includes the compound RD14 as a dopant and CBP as a host, the OLED of Ex174 to Ex182, in which the red EML includes the compound RD14 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 174, 175, 177, 178, 180 and 181, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD14 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     29. Comparative Example 15 (Ref15) 
     The compound RD15 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     30. Examples 
     (1) Examples 183 and 185 (Ex183 and Ex185) 
     The compound RD15 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 186 and 188 (Ex186 and Ex188) 
     The compound RD15 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 189 and 191 (Ex189 and Ex191) 
     The compound RD15 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 15 and Examples 183 to 191 are measured and listed in Table 15. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 15 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref15 
                 RD15 
                 CBP 
                 4.28 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex183 
                 RD15 
                 RHH-2 
                 REH-1 
                 4.19 
                 115 
                 116 
               
               
                 Ex184 
                 RD15 
                 RHH-2 
                 REH-11 
                 4.16 
                 113 
                 113 
               
               
                 Ex185 
                 RD15 
                 RHH-2 
                 REH-16 
                 4.17 
                 111 
                 109 
               
               
                 Ex186 
                 RD15 
                 RHH-8 
                 REH-1 
                 4.17 
                 116 
                 118 
               
               
                 Ex187 
                 RD15 
                 RHH-8 
                 REH-11 
                 4.16 
                 115 
                 114 
               
               
                 Ex188 
                 RD15 
                 RHH-8 
                 REH-16 
                 4.19 
                 111 
                 108 
               
               
                 Ex189 
                 RD15 
                 RHH-20 
                 REH-1 
                 4.17 
                 110 
                 116 
               
               
                 Ex190 
                 RD15 
                 RHH-20 
                 REH-11 
                 4.15 
                 108 
                 110 
               
               
                 Ex191 
                 RD15 
                 RHH-20 
                 REH-16 
                 4.17 
                 104 
                 108 
               
               
                   
               
            
           
         
       
     
     As shown in Table 15, in comparison to the OLED of Ref15, in which the red EML includes the compound RD15 as a dopant and CBP as a host, the OLED of Ex183 to Ex191, in which the red EML includes the compound RD15 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 183, 184, 186, 187, 189 and 190, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD15 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     31. Comparative Example 16 (Ref16) 
     The compound RD16 in Formula 8 and the compound (CBP) in Formula 7 are used as the dopant and host, respectively, to form the EML. 
     32. Examples 
     (1) Examples 192 and 194 (Ex192 and Ex194) 
     The compound RD16 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 195 and 197 (Ex195 and Ex197) 
     The compound RD16 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 198 and 200 (Ex198 and Ex200) 
     The compound RD16 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11 and REH-16 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 16 and Examples 192 to 200 are measured and listed in Table 16. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 16 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref16 
                 RD16 
                 CBP 
                 4.28 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex192 
                 RD16 
                 RHH-2 
                 REH-1 
                 4.19 
                 115 
                 117 
               
               
                 Ex193 
                 RD16 
                 RHH-2 
                 REH-11 
                 4.17 
                 112 
                 115 
               
               
                 Ex194 
                 RD16 
                 RHH-2 
                 REH-16 
                 4.18 
                 110 
                 110 
               
               
                 Ex195 
                 RD16 
                 RHH-8 
                 REH-1 
                 4.17 
                 119 
                 117 
               
               
                 Ex196 
                 RD16 
                 RHH-8 
                 REH-11 
                 4.16 
                 117 
                 113 
               
               
                 Ex197 
                 RD16 
                 RHH-8 
                 REH-16 
                 4.18 
                 113 
                 110 
               
               
                 Ex198 
                 RD16 
                 RHH-20 
                 REH-1 
                 4.17 
                 111 
                 117 
               
               
                 Ex199 
                 RD16 
                 RHH-20 
                 REH-11 
                 4.15 
                 109 
                 112 
               
               
                 Ex200 
                 RD16 
                 RHH-20 
                 REH-16 
                 4.16 
                 106 
                 111 
               
               
                   
               
            
           
         
       
     
     As shown in Table 16, in comparison to the OLED of Ref16, in which the red EML includes the compound RD16 as a dopant and CBP as a host, the OLED of Ex192 to Ex200, in which the red EML includes the compound RD16 as a dopant, the compound RHH-2, RHH-8 and RHH-20 as a first host, and the compound REH-1, REH-11 and REH-16 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 192, 193, 195, 196, 198 and 199, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8 and RHH-20 as the first host and the compound RD16 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     33. Comparative Example 17 (Ref17) 
     The compound RD17 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     34. Examples 
     (1) Examples 201 and 204 (Ex201 and Ex204) 
     The compound RD17 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 205 and 208 (Ex205 and Ex208) 
     The compound RD17 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 209 and 212 (Ex209 and Ex212) 
     The compound RD17 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 213 and 216 (Ex213 and Ex216) 
     The compound RD17 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 17 and Examples 201 to 216 are measured and listed in Table 17. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 17 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref17 
                 RD17 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex201 
                 RD17 
                 RHH-2 
                 REH-1 
                 4.20 
                 129 
                 137 
               
               
                 Ex202 
                 RD17 
                 RHH-2 
                 REH-11 
                 4.18 
                 127 
                 135 
               
               
                 Ex203 
                 RD17 
                 RHH-2 
                 REH-16 
                 4.21 
                 118 
                 121 
               
               
                 Ex204 
                 RD17 
                 RHH-2 
                 REH-30 
                 4.22 
                 119 
                 117 
               
               
                 Ex205 
                 RD17 
                 RHH-8 
                 REH-1 
                 4.15 
                 132 
                 140 
               
               
                 Ex206 
                 RD17 
                 RHH-8 
                 REH-11 
                 4.14 
                 124 
                 136 
               
               
                 Ex207 
                 RD17 
                 RHH-8 
                 REH-16 
                 4.18 
                 120 
                 125 
               
               
                 Ex208 
                 RD17 
                 RHH-8 
                 REH-30 
                 4.20 
                 117 
                 120 
               
               
                 Ex209 
                 RD17 
                 RHH-20 
                 REH-1 
                 4.13 
                 128 
                 135 
               
               
                 Ex210 
                 RD17 
                 RHH-20 
                 REH-11 
                 4.11 
                 127 
                 131 
               
               
                 Ex211 
                 RD17 
                 RHH-20 
                 REH-16 
                 4.15 
                 115 
                 127 
               
               
                 Ex212 
                 RD17 
                 RHH-20 
                 REH-30 
                 4.17 
                 113 
                 122 
               
               
                 Ex213 
                 RD17 
                 RHH-27 
                 REH-1 
                 4.18 
                 112 
                 131 
               
               
                 Ex214 
                 RD17 
                 RHH-27 
                 REH-11 
                 4.18 
                 111 
                 128 
               
               
                 Ex215 
                 RD17 
                 RHH-27 
                 REH-16 
                 4.21 
                 109 
                 119 
               
               
                 Ex216 
                 RD17 
                 RHH-27 
                 REH-30 
                 4.23 
                 109 
                 120 
               
               
                   
               
            
           
         
       
     
     As shown in Table 17, in comparison to the OLED of Ref17, in which the red EML includes the compound RD17 as a dopant and CBP as a host, the OLED of Ex201 to Ex216, in which the red EML includes the compound RD17 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 201 to 212, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD17 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 201, 202, 205, 206, 209, 210, 213 and 214, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD17 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     35. Comparative Example 18 (Ref18) 
     The compound RD18 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     36. Examples 
     (1) Examples 217 and 220 (Ex217 and Ex220) 
     The compound RD18 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 221 and 224 (Ex221 and Ex224) 
     The compound RD18 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 225 and 228 (Ex225 and Ex228) 
     The compound RD18 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 229 and 232 (Ex229 and Ex232) 
     The compound RD18 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 18 and Examples 217 to 232 are measured and listed in Table 18. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 18 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref18 
                 RD18 
                 CBP 
                 4.25 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex217 
                 RD18 
                 RHH-2 
                 REH-1 
                 4.13 
                 123 
                 134 
               
               
                 Ex218 
                 RD18 
                 RHH-2 
                 REH-11 
                 4.16 
                 120 
                 131 
               
               
                 Ex219 
                 RD18 
                 RHH-2 
                 REH-16 
                 4.17 
                 116 
                 123 
               
               
                 Ex220 
                 RD18 
                 RHH-2 
                 REH-30 
                 4.20 
                 113 
                 118 
               
               
                 Ex221 
                 RD18 
                 RHH-8 
                 REH-1 
                 4.11 
                 130 
                 137 
               
               
                 Ex222 
                 RD18 
                 RHH-8 
                 REH-11 
                 4.13 
                 123 
                 134 
               
               
                 Ex223 
                 RD18 
                 RHH-8 
                 REH-16 
                 4.17 
                 119 
                 128 
               
               
                 Ex224 
                 RD18 
                 RHH-8 
                 REH-30 
                 4.19 
                 118 
                 122 
               
               
                 Ex225 
                 RD18 
                 RHH-20 
                 REH-1 
                 4.15 
                 126 
                 132 
               
               
                 Ex226 
                 RD18 
                 RHH-20 
                 REH-11 
                 4.18 
                 121 
                 130 
               
               
                 Ex227 
                 RD18 
                 RHH-20 
                 REH-16 
                 4.17 
                 116 
                 123 
               
               
                 Ex228 
                 RD18 
                 RHH-20 
                 REH-30 
                 4.19 
                 112 
                 120 
               
               
                 Ex229 
                 RD18 
                 RHH-27 
                 REH-1 
                 4.16 
                 116 
                 129 
               
               
                 Ex230 
                 RD18 
                 RHH-27 
                 REH-11 
                 4.18 
                 113 
                 125 
               
               
                 Ex231 
                 RD18 
                 RHH-27 
                 REH-16 
                 4.20 
                 110 
                 118 
               
               
                 Ex232 
                 RD18 
                 RHH-27 
                 REH-30 
                 4.22 
                 111 
                 115 
               
               
                   
               
            
           
         
       
     
     As shown in Table 18, in comparison to the OLED of Ref18, in which the red EML includes the compound RD18 as a dopant and CBP as a host, the OLED of Ex217 to Ex232, in which the red EML includes the compound RD18 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 217 to 228, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD18 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 217, 218, 221, 222, 225, 226, 229 and 230, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD18 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     37. Comparative Example 19 (Ref19) 
     The compound RD19 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     38. Examples 
     (1) Examples 233 and 236 (Ex233 and Ex236) 
     The compound RD19 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 237 and 240 (Ex237 and Ex240) 
     The compound RD19 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 241 and 244 (Ex241 and Ex244) 
     The compound RD19 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 245 and 248 (Ex245 and Ex248) 
     The compound RD19 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 19 and Examples 233 to 248 are measured and listed in Table 19. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 19 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref19 
                 RD19 
                 CBP 
                 4.26 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex233 
                 RD19 
                 RHH-2 
                 REH-1 
                 4.17 
                 120 
                 121 
               
               
                 Ex234 
                 RD19 
                 RHH-2 
                 REH-11 
                 4.19 
                 117 
                 117 
               
               
                 Ex235 
                 RD19 
                 RHH-2 
                 REH-16 
                 4.20 
                 113 
                 114 
               
               
                 Ex236 
                 RD19 
                 RHH-2 
                 REH-30 
                 4.22 
                 108 
                 116 
               
               
                 Ex237 
                 RD19 
                 RHH-8 
                 REH-1 
                 4.16 
                 122 
                 126 
               
               
                 Ex238 
                 RD19 
                 RHH-8 
                 REH-11 
                 4.19 
                 119 
                 122 
               
               
                 Ex239 
                 RD19 
                 RHH-8 
                 REH-16 
                 4.20 
                 115 
                 116 
               
               
                 Ex240 
                 RD19 
                 RHH-8 
                 REH-30 
                 4.20 
                 111 
                 112 
               
               
                 Ex241 
                 RD19 
                 RHH-20 
                 REH-1 
                 4.18 
                 119 
                 120 
               
               
                 Ex242 
                 RD19 
                 RHH-20 
                 REH-11 
                 4.20 
                 115 
                 116 
               
               
                 Ex243 
                 RD19 
                 RHH-20 
                 REH-16 
                 4.21 
                 111 
                 112 
               
               
                 Ex244 
                 RD19 
                 RHH-20 
                 REH-30 
                 4.22 
                 108 
                 105 
               
               
                 Ex245 
                 RD19 
                 RHH-27 
                 REH-1 
                 4.20 
                 117 
                 118 
               
               
                 Ex246 
                 RD19 
                 RHH-27 
                 REH-11 
                 4.20 
                 114 
                 112 
               
               
                 Ex247 
                 RD19 
                 RHH-27 
                 REH-16 
                 4.22 
                 110 
                 108 
               
               
                 Ex248 
                 RD19 
                 RHH-27 
                 REH-30 
                 4.23 
                 110 
                 104 
               
               
                   
               
            
           
         
       
     
     As shown in Table 19, in comparison to the OLED of Ref19, in which the red EML includes the compound RD19 as a dopant and CBP as a host, the OLED of Ex233 to Ex248, in which the red EML includes the compound RD19 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 233 to 244, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD19 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 233, 234, 237, 238, 241, 242, 245 and 246, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD19 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     39. Comparative Example 20 (Ref20) 
     The compound RD20 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     40. Examples 
     (1) Examples 249 and 252 (Ex249 and Ex252) 
     The compound RD20 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 253 and 256 (Ex253 and Ex256) 
     The compound RD20 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 257 and 260 (Ex257 and Ex260) 
     The compound RD20 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 261 and 264 (Ex261 and Ex264) 
     The compound RD20 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 20 and Examples 249 to 264 are measured and listed in Table 20. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 20 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref20 
                 RD20 
                 CBP 
                 4.26 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex249 
                 RD20 
                 RHH-2 
                 REH-1 
                 4.18 
                 122 
                 123 
               
               
                 Ex250 
                 RD20 
                 RHH-2 
                 REH-11 
                 4.19 
                 118 
                 118 
               
               
                 Ex251 
                 RD20 
                 RHH-2 
                 REH-16 
                 4.21 
                 114 
                 115 
               
               
                 Ex252 
                 RD20 
                 RHH-2 
                 REH-30 
                 4.22 
                 109 
                 115 
               
               
                 Ex253 
                 RD20 
                 RHH-8 
                 REH-1 
                 4.17 
                 123 
                 128 
               
               
                 Ex254 
                 RD20 
                 RHH-8 
                 REH-11 
                 4.19 
                 120 
                 123 
               
               
                 Ex255 
                 RD20 
                 RHH-8 
                 REH-16 
                 4.20 
                 117 
                 118 
               
               
                 Ex256 
                 RD20 
                 RHH-8 
                 REH-30 
                 4.22 
                 112 
                 115 
               
               
                 Ex257 
                 RD20 
                 RHH-20 
                 REH-1 
                 4.18 
                 119 
                 121 
               
               
                 Ex258 
                 RD20 
                 RHH-20 
                 REH-11 
                 4.21 
                 116 
                 117 
               
               
                 Ex259 
                 RD20 
                 RHH-20 
                 REH-16 
                 4.23 
                 112 
                 115 
               
               
                 Ex260 
                 RD20 
                 RHH-20 
                 REH-30 
                 4.23 
                 110 
                 113 
               
               
                 Ex261 
                 RD20 
                 RHH-27 
                 REH-1 
                 4.19 
                 119 
                 119 
               
               
                 Ex262 
                 RD20 
                 RHH-27 
                 REH-11 
                 4.20 
                 115 
                 115 
               
               
                 Ex263 
                 RD20 
                 RHH-27 
                 REH-16 
                 4.21 
                 113 
                 111 
               
               
                 Ex264 
                 RD20 
                 RHH-27 
                 REH-30 
                 4.23 
                 112 
                 107 
               
               
                   
               
            
           
         
       
     
     As shown in Table 20, in comparison to the OLED of Ref20, in which the red EML includes the compound RD20 as a dopant and CBP as a host, the OLED of Ex249 to Ex264, in which the red EML includes the compound RD20 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 249 to 260, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD20 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 249, 250, 253, 254, 257, 258, 261 and 262, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD20 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     41. Comparative Example 21 (Ref21) 
     The compound RD21 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     42. Examples 
     (1) Examples 265 and 268 (Ex265 and Ex268) 
     The compound RD21 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 269 and 272 (Ex269 and Ex272) 
     The compound RD21 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 273 and 276 (Ex273 and Ex276) 
     The compound RD21 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 277 and 280 (Ex277 and Ex280) 
     The compound RD21 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 21 and Examples 265 to 280 are measured and listed in Table 21. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 21 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref21 
                 RD21 
                 CBP 
                 4.29 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex265 
                 RD21 
                 RHH-2 
                 REH-1 
                 4.22 
                 127 
                 135 
               
               
                 Ex266 
                 RD21 
                 RHH-2 
                 REH-11 
                 4.20 
                 124 
                 132 
               
               
                 Ex267 
                 RD21 
                 RHH-2 
                 REH-16 
                 4.25 
                 118 
                 120 
               
               
                 Ex268 
                 RD21 
                 RHH-2 
                 REH-30 
                 4.22 
                 118 
                 116 
               
               
                 Ex269 
                 RD21 
                 RHH-8 
                 REH-1 
                 4.17 
                 131 
                 137 
               
               
                 Ex270 
                 RD21 
                 RHH-8 
                 REH-11 
                 4.16 
                 124 
                 134 
               
               
                 Ex271 
                 RD21 
                 RHH-8 
                 REH-16 
                 4.22 
                 120 
                 124 
               
               
                 Ex272 
                 RD21 
                 RHH-8 
                 REH-30 
                 4.18 
                 118 
                 119 
               
               
                 Ex273 
                 RD21 
                 RHH-20 
                 REH-1 
                 4.15 
                 129 
                 133 
               
               
                 Ex274 
                 RD21 
                 RHH-20 
                 REH-11 
                 4.16 
                 126 
                 130 
               
               
                 Ex275 
                 RD21 
                 RHH-20 
                 REH-16 
                 4.17 
                 116 
                 126 
               
               
                 Ex276 
                 RD21 
                 RHH-20 
                 REH-30 
                 4.15 
                 113 
                 121 
               
               
                 Ex277 
                 RD21 
                 RHH-27 
                 REH-1 
                 4.20 
                 115 
                 129 
               
               
                 Ex278 
                 RD21 
                 RHH-27 
                 REH-11 
                 4.19 
                 111 
                 127 
               
               
                 Ex279 
                 RD21 
                 RHH-27 
                 REH-16 
                 4.23 
                 109 
                 117 
               
               
                 Ex280 
                 RD21 
                 RHH-27 
                 REH-30 
                 4.20 
                 110 
                 119 
               
               
                   
               
            
           
         
       
     
     As shown in Table 21, in comparison to the OLED of Ref21, in which the red EML includes the compound RD21 as a dopant and CBP as a host, the OLED of Ex265 to Ex280, in which the red EML includes the compound RD21 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 265 to 276, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD21 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 265, 266, 269, 270, 273, 274, 277 and 278, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD21 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     43. Comparative Example 22 (Ref20) 
     The compound RD22 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     44. Examples 
     (1) Examples 281 and 284 (Ex281 and Ex284) 
     The compound RD22 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 285 and 288 (Ex285 and Ex288) 
     The compound RD22 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 289 and 292 (Ex289 and Ex292) 
     The compound RD22 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 293 and 296 (Ex293 and Ex296) 
     The compound RD22 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 22 and Examples 281 to 296 are measured and listed in Table 22. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 22 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref22 
                 RD22 
                 CBP 
                 4.26 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex281 
                 RD22 
                 RHH-2 
                 REH-1 
                 4.14 
                 121 
                 130 
               
               
                 Ex282 
                 RD22 
                 RHH-2 
                 REH-11 
                 4.16 
                 118 
                 126 
               
               
                 Ex283 
                 RD22 
                 RHH-2 
                 REH-16 
                 4.18 
                 115 
                 120 
               
               
                 Ex284 
                 RD22 
                 RHH-2 
                 REH-30 
                 4.22 
                 112 
                 117 
               
               
                 Ex285 
                 RD22 
                 RHH-8 
                 REH-1 
                 4.13 
                 127 
                 135 
               
               
                 Ex286 
                 RD22 
                 RHH-8 
                 REH-11 
                 4.17 
                 124 
                 126 
               
               
                 Ex287 
                 RD22 
                 RHH-8 
                 REH-16 
                 4.18 
                 120 
                 122 
               
               
                 Ex288 
                 RD22 
                 RHH-8 
                 REH-30 
                 4.20 
                 118 
                 120 
               
               
                 Ex289 
                 RD22 
                 RHH-20 
                 REH-1 
                 4.17 
                 125 
                 131 
               
               
                 Ex290 
                 RD22 
                 RHH-20 
                 REH-11 
                 4.19 
                 120 
                 127 
               
               
                 Ex291 
                 RD22 
                 RHH-20 
                 REH-16 
                 4.21 
                 117 
                 123 
               
               
                 Ex292 
                 RD22 
                 RHH-20 
                 REH-30 
                 4.22 
                 113 
                 119 
               
               
                 Ex293 
                 RD22 
                 RHH-27 
                 REH-1 
                 4.18 
                 117 
                 128 
               
               
                 Ex294 
                 RD22 
                 RHH-27 
                 REH-11 
                 4.20 
                 114 
                 126 
               
               
                 Ex295 
                 RD22 
                 RHH-27 
                 REH-16 
                 4.22 
                 111 
                 119 
               
               
                 Ex296 
                 RD22 
                 RHH-27 
                 REH-30 
                 4.23 
                 110 
                 113 
               
               
                   
               
            
           
         
       
     
     As shown in Table 22, in comparison to the OLED of Ref22, in which the red EML includes the compound RD22 as a dopant and CBP as a host, the OLED of Ex281 to Ex296, in which the red EML includes the compound RD22 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 281 to 292, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD22 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 281, 282, 285, 286, 289, 290, 293 and 294, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD22 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     45. Comparative Example 23 (Ref23) 
     The compound RD23 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     46. Examples 
     (1) Examples 297 and 300 (Ex297 and Ex300) 
     The compound RD23 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 301 and 304 (Ex301 and Ex304) 
     The compound RD23 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 305 and 308 (Ex305 and Ex308) 
     The compound RD23 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 309 and 312 (Ex309 and Ex312) 
     The compound RD23 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 23 and Examples 297 to 312 are measured and listed in Table 23. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 23 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref23 
                 RD23 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex297 
                 RD23 
                 RHH-2 
                 REH-1 
                 4.18 
                 118 
                 120 
               
               
                 Ex298 
                 RD23 
                 RHH-2 
                 REH-11 
                 4.19 
                 115 
                 116 
               
               
                 Ex299 
                 RD23 
                 RHH-2 
                 REH-16 
                 4.21 
                 112 
                 113 
               
               
                 Ex300 
                 RD23 
                 RHH-2 
                 REH-30 
                 4.23 
                 107 
                 112 
               
               
                 Ex301 
                 RD23 
                 RHH-8 
                 REH-1 
                 4.17 
                 120 
                 125 
               
               
                 Ex302 
                 RD23 
                 RHH-8 
                 REH-11 
                 4.19 
                 117 
                 120 
               
               
                 Ex303 
                 RD23 
                 RHH-8 
                 REH-16 
                 4.20 
                 113 
                 114 
               
               
                 Ex304 
                 RD23 
                 RHH-8 
                 REH-30 
                 4.22 
                 110 
                 110 
               
               
                 Ex305 
                 RD23 
                 RHH-20 
                 REH-1 
                 4.19 
                 115 
                 119 
               
               
                 Ex306 
                 RD23 
                 RHH-20 
                 REH-11 
                 4.20 
                 113 
                 115 
               
               
                 Ex307 
                 RD23 
                 RHH-20 
                 REH-16 
                 4.22 
                 108 
                 111 
               
               
                 Ex308 
                 RD23 
                 RHH-20 
                 REH-30 
                 4.23 
                 105 
                 108 
               
               
                 Ex309 
                 RD23 
                 RHH-27 
                 REH-1 
                 4.19 
                 115 
                 116 
               
               
                 Ex310 
                 RD23 
                 RHH-27 
                 REH-11 
                 4.21 
                 112 
                 111 
               
               
                 Ex311 
                 RD23 
                 RHH-27 
                 REH-16 
                 4.22 
                 107 
                 107 
               
               
                 Ex312 
                 RD23 
                 RHH-27 
                 REH-30 
                 4.24 
                 107 
                 105 
               
               
                   
               
            
           
         
       
     
     As shown in Table 23, in comparison to the OLED of Ref23, in which the red EML includes the compound RD23 as a dopant and CBP as a host, the OLED of Ex297 to Ex312, in which the red EML includes the compound RD23 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 297 to 308, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD23 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 297, 298, 301, 302, 305, 306, 309 and 310, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD23 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     47. Comparative Example 24 (Ref24) 
     The compound RD24 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     48. Examples 
     (1) Examples 313 and 316 (Ex313 and Ex316) 
     The compound RD24 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 317 and 320 (Ex317 and Ex320) 
     The compound RD24 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 321 and 324 (Ex321 and Ex324) 
     The compound RD24 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 325 and 328 (Ex325 and Ex328) 
     The compound RD24 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 24 and Examples 313 to 328 are measured and listed in Table 24. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 24 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref24 
                 RD24 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex313 
                 RD24 
                 RHH-2 
                 REH-1 
                 4.17 
                 119 
                 120 
               
               
                 Ex314 
                 RD24 
                 RHH-2 
                 REH-11 
                 4.19 
                 116 
                 117 
               
               
                 Ex315 
                 RD24 
                 RHH-2 
                 REH-16 
                 4.21 
                 111 
                 113 
               
               
                 Ex316 
                 RD24 
                 RHH-2 
                 REH-30 
                 4.22 
                 106 
                 111 
               
               
                 Ex317 
                 RD24 
                 RHH-8 
                 REH-1 
                 4.16 
                 121 
                 126 
               
               
                 Ex318 
                 RD24 
                 RHH-8 
                 REH-11 
                 4.18 
                 117 
                 120 
               
               
                 Ex319 
                 RD24 
                 RHH-8 
                 REH-16 
                 4.19 
                 115 
                 115 
               
               
                 Ex320 
                 RD24 
                 RHH-8 
                 REH-30 
                 4.21 
                 112 
                 111 
               
               
                 Ex321 
                 RD24 
                 RHH-20 
                 REH-1 
                 4.19 
                 116 
                 120 
               
               
                 Ex322 
                 RD24 
                 RHH-20 
                 REH-11 
                 4.20 
                 114 
                 116 
               
               
                 Ex323 
                 RD24 
                 RHH-20 
                 REH-16 
                 4.23 
                 110 
                 113 
               
               
                 Ex324 
                 RD24 
                 RHH-20 
                 REH-30 
                 4.22 
                 106 
                 109 
               
               
                 Ex325 
                 RD24 
                 RHH-27 
                 REH-1 
                 4.20 
                 116 
                 117 
               
               
                 Ex326 
                 RD24 
                 RHH-27 
                 REH-11 
                 4.21 
                 113 
                 112 
               
               
                 Ex327 
                 RD24 
                 RHH-27 
                 REH-16 
                 4.23 
                 107 
                 109 
               
               
                 Ex328 
                 RD24 
                 RHH-27 
                 REH-30 
                 4.25 
                 105 
                 106 
               
               
                   
               
            
           
         
       
     
     As shown in Table 24, in comparison to the OLED of Ref24, in which the red EML includes the compound RD24 as a dopant and CBP as a host, the OLED of Ex313 to Ex328, in which the red EML includes the compound RD24 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 313 to 324, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD24 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 313, 314, 317, 318, 321, 322, 325 and 326, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD24 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     49. Comparative Example 25 (Ref25) 
     The compound RD25 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     50. Examples 
     (1) Examples 329 and 332 (Ex329 and Ex332) 
     The compound RD25 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 333 and 336 (Ex333 and Ex336) 
     The compound RD25 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 337 and 340 (Ex337 and Ex340) 
     The compound RD25 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 341 and 344 (Ex341 and Ex344) 
     The compound RD25 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 25 and Examples 329 to 344 are measured and listed in Table 25. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 25 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref25 
                 RD25 
                 CBP 
                 4.29 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex329 
                 RD25 
                 RHH-2 
                 REH-1 
                 4.21 
                 126 
                 134 
               
               
                 Ex330 
                 RD25 
                 RHH-2 
                 REH-11 
                 4.20 
                 124 
                 130 
               
               
                 Ex331 
                 RD25 
                 RHH-2 
                 REH-16 
                 4.22 
                 120 
                 121 
               
               
                 Ex332 
                 RD25 
                 RHH-2 
                 REH-30 
                 4.23 
                 118 
                 118 
               
               
                 Ex333 
                 RD25 
                 RHH-8 
                 REH-1 
                 4.18 
                 129 
                 135 
               
               
                 Ex334 
                 RD25 
                 RHH-8 
                 REH-11 
                 4.16 
                 123 
                 132 
               
               
                 Ex335 
                 RD25 
                 RHH-8 
                 REH-16 
                 4.19 
                 118 
                 122 
               
               
                 Ex336 
                 RD25 
                 RHH-8 
                 REH-30 
                 4.20 
                 117 
                 118 
               
               
                 Ex337 
                 RD25 
                 RHH-20 
                 REH-1 
                 4.16 
                 126 
                 133 
               
               
                 Ex338 
                 RD25 
                 RHH-20 
                 REH-11 
                 4.15 
                 126 
                 129 
               
               
                 Ex339 
                 RD25 
                 RHH-20 
                 REH-16 
                 4.17 
                 114 
                 125 
               
               
                 Ex340 
                 RD25 
                 RHH-20 
                 REH-30 
                 4.19 
                 113 
                 122 
               
               
                 Ex341 
                 RD25 
                 RHH-27 
                 REH-1 
                 4.19 
                 111 
                 127 
               
               
                 Ex342 
                 RD25 
                 RHH-27 
                 REH-11 
                 4.19 
                 110 
                 125 
               
               
                 Ex343 
                 RD25 
                 RHH-27 
                 REH-16 
                 4.22 
                 108 
                 114 
               
               
                 Ex344 
                 RD25 
                 RHH-27 
                 REH-30 
                 4.23 
                 109 
                 113 
               
               
                   
               
            
           
         
       
     
     As shown in Table 25, in comparison to the OLED of Ref25, in which the red EML includes the compound RD25 as a dopant and CBP as a host, the OLED of Ex329 to Ex344, in which the red EML includes the compound RD25 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 329 to 340, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD25 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 329, 330, 333, 334, 337, 338, 341 and 342, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD25 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     51. Comparative Example 26 (Ref26) 
     The compound RD26 in Formula 8 as the dopant and the compound (CBP) in 
     Formula 7 as the host are used to form the EML. 
     52. Examples 
     (1) Examples 345 and 348 (Ex345 and Ex348) 
     The compound RD26 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 349 and 352 (Ex349 and Ex352) 
     The compound RD26 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 353 and 356 (Ex353 and Ex356) 
     The compound RD26 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 357 and 360 (Ex357 and Ex360) 
     The compound RD26 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 26 and Examples 345 to 360 are measured and listed in Table 26. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 26 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref26 
                 RD26 
                 CBP 
                 4.26 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex345 
                 RD26 
                 RHH-2 
                 REH-1 
                 4.15 
                 121 
                 131 
               
               
                 Ex346 
                 RD26 
                 RHH-2 
                 REH-11 
                 4.16 
                 117 
                 127 
               
               
                 Ex347 
                 RD26 
                 RHH-2 
                 REH-16 
                 4.18 
                 115 
                 121 
               
               
                 Ex348 
                 RD26 
                 RHH-2 
                 REH-30 
                 4.23 
                 110 
                 118 
               
               
                 Ex349 
                 RD26 
                 RHH-8 
                 REH-1 
                 4.13 
                 126 
                 134 
               
               
                 Ex350 
                 RD26 
                 RHH-8 
                 REH-11 
                 4.17 
                 123 
                 126 
               
               
                 Ex351 
                 RD26 
                 RHH-8 
                 REH-16 
                 4.19 
                 119 
                 121 
               
               
                 Ex352 
                 RD26 
                 RHH-8 
                 REH-30 
                 4.22 
                 116 
                 121 
               
               
                 Ex353 
                 RD26 
                 RHH-20 
                 REH-1 
                 4.17 
                 124 
                 130 
               
               
                 Ex354 
                 RD26 
                 RHH-20 
                 REH-11 
                 4.18 
                 120 
                 127 
               
               
                 Ex355 
                 RD26 
                 RHH-20 
                 REH-16 
                 4.22 
                 117 
                 122 
               
               
                 Ex356 
                 RD26 
                 RHH-20 
                 REH-30 
                 4.23 
                 115 
                 118 
               
               
                 Ex357 
                 RD26 
                 RHH-27 
                 REH-1 
                 4.18 
                 118 
                 127 
               
               
                 Ex358 
                 RD26 
                 RHH-27 
                 REH-11 
                 4.19 
                 113 
                 124 
               
               
                 Ex359 
                 RD26 
                 RHH-27 
                 REH-16 
                 4.21 
                 110 
                 117 
               
               
                 Ex360 
                 RD26 
                 RHH-27 
                 REH-30 
                 4.22 
                 108 
                 114 
               
               
                   
               
            
           
         
       
     
     As shown in Table 26, in comparison to the OLED of Ref26, in which the red EML includes the compound RD26 as a dopant and CBP as a host, the OLED of Ex345 to Ex360, in which the red EML includes the compound RD26 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 345 to 356, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD26 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 345, 346, 349, 350, 353, 354, 357 and 358, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD26 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     53. Comparative Example 27 (Ref27) 
     The compound RD27 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     54. Examples 
     (1) Examples 361 and 364 (Ex361 and Ex364) 
     The compound RD27 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 365 and 368 (Ex365 and Ex368) 
     The compound RD27 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 369 and 372 (Ex369 and Ex372) 
     The compound RD27 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 373 and 376 (Ex373 and Ex376) 
     The compound RD27 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 27 and Examples 361 to 376 are measured and listed in Table 27. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 27 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref27 
                 RD27 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex361 
                 RD27 
                 RHH-2 
                 REH-1 
                 4.19 
                 119 
                 122 
               
               
                 Ex362 
                 RD27 
                 RHH-2 
                 REH-11 
                 4.19 
                 115 
                 118 
               
               
                 Ex363 
                 RD27 
                 RHH-2 
                 REH-16 
                 4.21 
                 113 
                 114 
               
               
                 Ex364 
                 RD27 
                 RHH-2 
                 REH-30 
                 4.22 
                 108 
                 111 
               
               
                 Ex365 
                 RD27 
                 RHH-8 
                 REH-1 
                 4.17 
                 121 
                 127 
               
               
                 Ex366 
                 RD27 
                 RHH-8 
                 REH-11 
                 4.18 
                 117 
                 121 
               
               
                 Ex367 
                 RD27 
                 RHH-8 
                 REH-16 
                 4.20 
                 112 
                 117 
               
               
                 Ex368 
                 RD27 
                 RHH-8 
                 REH-30 
                 4.21 
                 109 
                 113 
               
               
                 Ex369 
                 RD27 
                 RHH-20 
                 REH-1 
                 4.19 
                 116 
                 120 
               
               
                 Ex370 
                 RD27 
                 RHH-20 
                 REH-11 
                 4.20 
                 113 
                 116 
               
               
                 Ex371 
                 RD27 
                 RHH-20 
                 REH-16 
                 4.20 
                 110 
                 112 
               
               
                 Ex372 
                 RD27 
                 RHH-20 
                 REH-30 
                 4.22 
                 108 
                 109 
               
               
                 Ex373 
                 RD27 
                 RHH-27 
                 REH-1 
                 4.20 
                 116 
                 118 
               
               
                 Ex374 
                 RD27 
                 RHH-27 
                 REH-11 
                 4.21 
                 111 
                 113 
               
               
                 Ex375 
                 RD27 
                 RHH-27 
                 REH-16 
                 4.22 
                 109 
                 108 
               
               
                 Ex376 
                 RD27 
                 RHH-27 
                 REH-30 
                 4.23 
                 108 
                 106 
               
               
                   
               
            
           
         
       
     
     As shown in Table 27, in comparison to the OLED of Ref27, in which the red EML includes the compound RD27 as a dopant and CBP as a host, the OLED of Ex361 to Ex376, in which the red EML includes the compound RD27 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 361 to 372, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD27 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 361, 362, 365, 366, 369, 370, 373 and 374, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD27 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     55. Comparative Example 28 (Ref28) 
     The compound RD28 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     56. Examples 
     (1) Examples 377 and 380 (Ex377 and Ex380) 
     The compound RD28 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 381 and 384 (Ex381 and Ex384) 
     The compound RD28 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 385 and 388 (Ex385 and Ex388) 
     The compound RD28 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 389 and 392 (Ex389 and Ex392) 
     The compound RD28 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 28 and Examples 377 to 392 are measured and listed in Table 28. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 28 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref28 
                 RD28 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex377 
                 RD28 
                 RHH-2 
                 REH-1 
                 4.17 
                 118 
                 122 
               
               
                 Ex378 
                 RD28 
                 RHH-2 
                 REH-11 
                 4.19 
                 114 
                 118 
               
               
                 Ex379 
                 RD28 
                 RHH-2 
                 REH-16 
                 4.20 
                 110 
                 114 
               
               
                 Ex380 
                 RD28 
                 RHH-2 
                 REH-30 
                 4.22 
                 105 
                 112 
               
               
                 Ex381 
                 RD28 
                 RHH-8 
                 REH-1 
                 4.15 
                 123 
                 125 
               
               
                 Ex382 
                 RD28 
                 RHH-8 
                 REH-11 
                 4.16 
                 119 
                 121 
               
               
                 Ex383 
                 RD28 
                 RHH-8 
                 REH-16 
                 4.19 
                 115 
                 117 
               
               
                 Ex384 
                 RD28 
                 RHH-8 
                 REH-30 
                 4.20 
                 111 
                 113 
               
               
                 Ex385 
                 RD28 
                 RHH-20 
                 REH-1 
                 4.18 
                 117 
                 119 
               
               
                 Ex386 
                 RD28 
                 RHH-20 
                 REH-11 
                 4.20 
                 114 
                 114 
               
               
                 Ex387 
                 RD28 
                 RHH-20 
                 REH-16 
                 4.22 
                 111 
                 112 
               
               
                 Ex388 
                 RD28 
                 RHH-20 
                 REH-30 
                 4.23 
                 107 
                 110 
               
               
                 Ex389 
                 RD28 
                 RHH-27 
                 REH-1 
                 4.19 
                 115 
                 118 
               
               
                 Ex390 
                 RD28 
                 RHH-27 
                 REH-11 
                 4.20 
                 112 
                 113 
               
               
                 Ex391 
                 RD28 
                 RHH-27 
                 REH-16 
                 4.22 
                 108 
                 110 
               
               
                 Ex392 
                 RD28 
                 RHH-27 
                 REH-30 
                 4.24 
                 107 
                 108 
               
               
                   
               
            
           
         
       
     
     As shown in Table 28, in comparison to the OLED of Ref28, in which the red EML includes the compound RD28 as a dopant and CBP as a host, the OLED of Ex377 to Ex392, in which the red EML includes the compound RD28 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 377 to 388, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD28 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 377, 378, 381, 382, 385, 386, 389 and 390, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD28 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     57. Comparative Example 29 (Ref29) 
     The compound RD29 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     58. Examples 
     (1) Examples 393 and 396 (Ex393 and Ex396) 
     The compound RD29 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 397 and 400 (Ex397 and Ex400) 
     The compound RD29 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 401 and 404 (Ex401 and Ex404) 
     The compound RD29 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 405 and 408 (Ex405 and Ex408) 
     The compound RD29 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 29 and Examples 393 to 408 are measured and listed in Table 29. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 29 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref29 
                 RD29 
                 CBP 
                 4.30 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex393 
                 RD29 
                 RHH-2 
                 REH-1 
                 4.23 
                 125 
                 131 
               
               
                 Ex394 
                 RD29 
                 RHH-2 
                 REH-11 
                 4.21 
                 122 
                 129 
               
               
                 Ex395 
                 RD29 
                 RHH-2 
                 REH-16 
                 4.24 
                 120 
                 119 
               
               
                 Ex396 
                 RD29 
                 RHH-2 
                 REH-30 
                 4.24 
                 117 
                 115 
               
               
                 Ex397 
                 RD29 
                 RHH-8 
                 REH-1 
                 4.18 
                 128 
                 135 
               
               
                 Ex398 
                 RD29 
                 RHH-8 
                 REH-11 
                 4.17 
                 118 
                 132 
               
               
                 Ex399 
                 RD29 
                 RHH-8 
                 REH-16 
                 4.20 
                 117 
                 122 
               
               
                 Ex400 
                 RD29 
                 RHH-8 
                 REH-30 
                 4.20 
                 116 
                 118 
               
               
                 Ex401 
                 RD29 
                 RHH-20 
                 REH-1 
                 4.16 
                 124 
                 131 
               
               
                 Ex402 
                 RD29 
                 RHH-20 
                 REH-11 
                 4.15 
                 122 
                 128 
               
               
                 Ex403 
                 RD29 
                 RHH-20 
                 REH-16 
                 4.19 
                 114 
                 125 
               
               
                 Ex404 
                 RD29 
                 RHH-20 
                 REH-30 
                 4.20 
                 111 
                 120 
               
               
                 Ex405 
                 RD29 
                 RHH-27 
                 REH-1 
                 4.21 
                 111 
                 127 
               
               
                 Ex406 
                 RD29 
                 RHH-27 
                 REH-11 
                 4.22 
                 107 
                 126 
               
               
                 Ex407 
                 RD29 
                 RHH-27 
                 REH-16 
                 4.23 
                 106 
                 115 
               
               
                 Ex408 
                 RD29 
                 RHH-27 
                 REH-30 
                 4.24 
                 107 
                 116 
               
               
                   
               
            
           
         
       
     
     As shown in Table 29, in comparison to the OLED of Ref29, in which the red EML includes the compound RD29 as a dopant and CBP as a host, the OLED of Ex393 to Ex408, in which the red EML includes the compound RD29 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 393 to 404, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD29 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 393, 394, 397, 398, 401, 402, 405 and 406, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD29 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     59. Comparative Example 30 (Ref30) 
     The compound RD30 in Formula 8 as the dopant and the compound (CBP) in 
     Formula 7 as the host are used to form the EML. 
     60. Examples 
     (1) Examples 409 and 412 (Ex409 and Ex412) 
     The compound RD30 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 413 and 416 (Ex413 and Ex416) 
     The compound RD30 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 417 and 420 (Ex417 and Ex420) 
     The compound RD30 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 421 and 424 (Ex421 and Ex424) 
     The compound RD30 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 30 and Examples 409 to 424 are measured and listed in Table 30. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 30 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref30 
                 RD30 
                 CBP 
                 4.26 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex409 
                 RD30 
                 RHH-2 
                 REH-1 
                 4.16 
                 120 
                 130 
               
               
                 Ex410 
                 RD30 
                 RHH-2 
                 REH-11 
                 4.16 
                 117 
                 126 
               
               
                 Ex411 
                 RD30 
                 RHH-2 
                 REH-16 
                 4.19 
                 114 
                 122 
               
               
                 Ex412 
                 RD30 
                 RHH-2 
                 REH-30 
                 4.22 
                 108 
                 118 
               
               
                 Ex413 
                 RD30 
                 RHH-8 
                 REH-1 
                 4.14 
                 125 
                 134 
               
               
                 Ex414 
                 RD30 
                 RHH-8 
                 REH-11 
                 4.17 
                 122 
                 127 
               
               
                 Ex415 
                 RD30 
                 RHH-8 
                 REH-16 
                 4.19 
                 117 
                 123 
               
               
                 Ex416 
                 RD30 
                 RHH-8 
                 REH-30 
                 4.21 
                 115 
                 120 
               
               
                 Ex417 
                 RD30 
                 RHH-20 
                 REH-1 
                 4.16 
                 122 
                 129 
               
               
                 Ex418 
                 RD30 
                 RHH-20 
                 REH-11 
                 4.18 
                 118 
                 125 
               
               
                 Ex419 
                 RD30 
                 RHH-20 
                 REH-16 
                 4.20 
                 115 
                 121 
               
               
                 Ex420 
                 RD30 
                 RHH-20 
                 REH-30 
                 4.22 
                 112 
                 119 
               
               
                 Ex421 
                 RD30 
                 RHH-27 
                 REH-1 
                 4.18 
                 118 
                 126 
               
               
                 Ex422 
                 RD30 
                 RHH-27 
                 REH-11 
                 4.19 
                 114 
                 123 
               
               
                 Ex423 
                 RD30 
                 RHH-27 
                 REH-16 
                 4.20 
                 111 
                 118 
               
               
                 Ex424 
                 RD30 
                 RHH-27 
                 REH-30 
                 4.22 
                 110 
                 113 
               
               
                   
               
            
           
         
       
     
     As shown in Table 30, in comparison to the OLED of Ref30, in which the red EML includes the compound RD30 as a dopant and CBP as a host, the OLED of Ex409 to Ex424, in which the red EML includes the compound RD30 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 409 to 420, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD30 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 409, 410, 413, 414, 417, 418, 421 and 422, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD30 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     61. Comparative Example 31 (Ref31) 
     The compound RD31 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     62. Examples 
     (1) Examples 425 and 428 (Ex425 and Ex428) 
     The compound RD31 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 429 and 432 (Ex429 and Ex432) 
     The compound RD31 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 433 and 436 (Ex433 and Ex436) 
     The compound RD31 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 437 and 440 (Ex437 and Ex440) 
     The compound RD31 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 31 and Examples 425 to 440 are measured and listed in Table 31. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 31 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref31 
                 RD31 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex425 
                 RD31 
                 RHH-2 
                 REH-1 
                 4.18 
                 118 
                 121 
               
               
                 Ex426 
                 RD31 
                 RHH-2 
                 REH-11 
                 4.19 
                 115 
                 117 
               
               
                 Ex427 
                 RD31 
                 RHH-2 
                 REH-16 
                 4.20 
                 112 
                 114 
               
               
                 Ex428 
                 RD31 
                 RHH-2 
                 REH-30 
                 4.22 
                 110 
                 110 
               
               
                 Ex429 
                 RD31 
                 RHH-8 
                 REH-1 
                 4.16 
                 124 
                 126 
               
               
                 Ex430 
                 RD31 
                 RHH-8 
                 REH-11 
                 4.18 
                 118 
                 121 
               
               
                 Ex431 
                 RD31 
                 RHH-8 
                 REH-16 
                 4.19 
                 113 
                 118 
               
               
                 Ex432 
                 RD31 
                 RHH-8 
                 REH-30 
                 4.20 
                 111 
                 114 
               
               
                 Ex433 
                 RD31 
                 RHH-20 
                 REH-1 
                 4.18 
                 117 
                 118 
               
               
                 Ex434 
                 RD31 
                 RHH-20 
                 REH-11 
                 4.20 
                 112 
                 115 
               
               
                 Ex435 
                 RD31 
                 RHH-20 
                 REH-16 
                 4.21 
                 109 
                 112 
               
               
                 Ex436 
                 RD31 
                 RHH-20 
                 REH-30 
                 4.22 
                 106 
                 108 
               
               
                 Ex437 
                 RD31 
                 RHH-27 
                 REH-1 
                 4.19 
                 116 
                 117 
               
               
                 Ex438 
                 RD31 
                 RHH-27 
                 REH-11 
                 4.21 
                 113 
                 112 
               
               
                 Ex439 
                 RD31 
                 RHH-27 
                 REH-16 
                 4.22 
                 108 
                 109 
               
               
                 Ex440 
                 RD31 
                 RHH-27 
                 REH-30 
                 4.24 
                 106 
                 107 
               
               
                   
               
            
           
         
       
     
     As shown in Table 31, in comparison to the OLED of Ref31, in which the red EML includes the compound RD31 as a dopant and CBP as a host, the OLED of Ex425 to Ex440, in which the red EML includes the compound RD31 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 425 to 436, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD31 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 425, 426, 429, 430, 433, 434, 437 and 438, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD31 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     63. Comparative Example 32 (Ref32) 
     The compound RD32 in Formula 8 as the dopant and the compound (CBP) in Formula 7 as the host are used to form the EML. 
     64. Examples 
     (1) Examples 441 and 444 (Ex441 and Ex444) 
     The compound RD32 in Formula 8 as the dopant, the compound RHH-2 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (2) Examples 445 and 448 (Ex445 and Ex448) 
     The compound RD32 in Formula 8 as the dopant, the compound RHH-8 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (3) Examples 449 and 452 (Ex449 and Ex452) 
     The compound RD32 in Formula 8 as the dopant, the compound RHH-20 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     (4) Examples 453 and 456 (Ex453 and Ex456) 
     The compound RD32 in Formula 8 as the dopant, the compound RHH-27 in Formula 2-2 as a first host, and the compounds REH-1, REH-11, REH-16 and REH-30 in Formula 3-4 as a second dopant are used to form the EML. (first host:second host=1:1 (weight %)) 
     The properties, i.e., the driving voltage (V), the external quantum efficiency (EQE) and the lifespan (LT95), of the OLEDs manufactured in Comparative Example 32 and Examples 441 to 456 are measured and listed in Table 32. The properties of the OLED were measured at the room temperature using a current source (KEITHLEY) and a photometer (PR 650). The driving voltage and the external quantum efficiency were measured under the condition of a current density of 10 mA/cm 2 , and the lifespan (the time to reach 95% of the lifespan) was measured at 40° C. under 40 mA/cm 2  condition. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 32 
               
             
            
               
                   
                   
               
               
                   
                 EML 
                   
                 EQE 
                 LT95 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Dopant 
                 Host 
                 V 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Ref32 
                 RD32 
                 CBP 
                 4.27 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ex441 
                 RD32 
                 RHH-2 
                 REH-1 
                 4.17 
                 119 
                 121 
               
               
                 Ex442 
                 RD32 
                 RHH-2 
                 REH-11 
                 4.19 
                 113 
                 117 
               
               
                 Ex443 
                 RD32 
                 RHH-2 
                 REH-16 
                 4.21 
                 110 
                 114 
               
               
                 Ex444 
                 RD32 
                 RHH-2 
                 REH-30 
                 4.23 
                 107 
                 110 
               
               
                 Ex445 
                 RD32 
                 RHH-8 
                 REH-1 
                 4.16 
                 121 
                 125 
               
               
                 Ex446 
                 RD32 
                 RHH-8 
                 REH-11 
                 4.17 
                 117 
                 120 
               
               
                 Ex447 
                 RD32 
                 RHH-8 
                 REH-16 
                 4.19 
                 113 
                 116 
               
               
                 Ex448 
                 RD32 
                 RHH-8 
                 REH-30 
                 4.19 
                 110 
                 112 
               
               
                 Ex449 
                 RD32 
                 RHH-20 
                 REH-1 
                 4.18 
                 116 
                 118 
               
               
                 Ex450 
                 RD32 
                 RHH-20 
                 REH-11 
                 4.19 
                 113 
                 113 
               
               
                 Ex451 
                 RD32 
                 RHH-20 
                 REH-16 
                 4.21 
                 110 
                 110 
               
               
                 Ex452 
                 RD32 
                 RHH-20 
                 REH-30 
                 4.23 
                 108 
                 110 
               
               
                 Ex453 
                 RD32 
                 RHH-27 
                 REH-1 
                 4.18 
                 116 
                 119 
               
               
                 Ex454 
                 RD32 
                 RHH-27 
                 REH-11 
                 4.19 
                 110 
                 114 
               
               
                 Ex455 
                 RD32 
                 RHH-27 
                 REH-16 
                 4.21 
                 108 
                 112 
               
               
                 Ex456 
                 RD32 
                 RHH-27 
                 REH-30 
                 4.23 
                 106 
                 110 
               
               
                   
               
            
           
         
       
     
     As shown in Table 32, in comparison to the OLED of Ref32, in which the red EML includes the compound RD32 as a dopant and CBP as a host, the OLED of Ex441 to Ex456, in which the red EML includes the compound RD32 as a dopant, the compound RHH-2, RHH-8, RHH-20 and RHH-27 as a first host, and the compound REH-1, REH-11, REH-16 and REH-30 as a second host, has advantages in the driving voltage, the luminous efficiency and the luminous lifespan. 
     In addition, as Examples 441 to 448, when the compound RHH-2, RHH-8 or RHH-20 as the first host with the compound REH-1, REH-11, REH-16 or REH-30 as the second host and the compound RD32 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the first host being the compound in Formula 2-1, in which one of X 1  and X 2  is N, the other one of X 1  and X 2  is O, and each of R 1  to R 3  is an unsubstituted or substituted C 6 -C 30  aryl group, with the second host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     Moreover, as Examples 441, 442, 445, 446, 449, 450, 453 and 454, when the compound REH-1 or REH-11 as the second host with the compound RHH-2, RHH-8, RHH-20 or RHH-27 as the first host and the compound RD32 as the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. Namely, when the second host being the compound in one of Formulas 3-1 to 3-3, in which X is NR 2  and R 2  is an unsubstituted or substituted C 6 -C 30  aryl group, with the first host and the dopant are included in the red EML, the luminous efficiency and the luminous lifespan of the OLED are significantly increased. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the invention. Thus, it is intended that the present disclosure cover the modifications and variations of the present disclosure provided they come within the scope of the appended claims.