Patent Publication Number: US-2019194234-A1

Title: Metal complexes containing heterocycle substituted ligands, and electroluminescent devices and formulations containing the complexes

Description:
This application claims the benefit of U.S. Provisional Application No. 62/610,273, filed Dec. 25, 2017, the entire content of which is incorporated herein by reference. 
    
    
     1 FIELD OF THE INVENTION 
     The present invention relates to a compound for organic electronic devices, such as organic light emitting devices. More specifically, the present invention relates to a metal complex comprising heterocycle-substituted ligands, an organic electroluminescent device and a formulation comprising the metal complex. 
     2 BACKGROUND ART 
     An organic electronic device is preferably selected from the group consisting of organic light-emitting diodes (OLEDs), organic field-effect transistors (O-FETs), organic light-emitting transistors (OLETs), organic photovoltaic devices (OPVs), dye-sensitized solar cells (DSSCs), organic optical detectors, organic photoreceptors, organic field-quench devices (OFQDs), light-emitting electrochemical cells (LECs), organic laser diodes and organic plasmon emitting devices. 
     In 1987, Tang and Van Slyke of Eastman Kodak reported a bilayer organic electroluminescent device, which comprises an arylamine hole transporting layer and a tris-8-hydroxyquinolato-aluminum layer as the electron and emitting layer (Applied Physics Letters, 1987, 51 (12): 913-915). Once a bias is applied to the device, green light was emitted from the device. This invention laid the foundation for the development of modern organic light-emitting diodes (OLEDs). State-of-the-art OLEDs may comprise multiple layers such as charge injection and transporting layers, charge and exciton blocking layers, and one or multiple emissive layers between the cathode and anode. Since OLED is a self-emitting solid state device, it offers tremendous potential for display and lighting applications. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on flexible substrates. 
     OLED can be categorized as three different types according to its emitting mechanism. The OLED invented by Tang and van Slyke is a fluorescent OLED. It only utilizes singlet emission. The triplets generated in the device are wasted through nonradiative decay channels. Therefore, the internal quantum efficiency (IQE) of a fluorescent OLED is only 25%. This limitation hindered the commercialization of OLED. In 1997, Forrest and Thompson reported phosphorescent OLED, which uses triplet emission from heave metal containing complexes as the emitter. As a result, both singlet and triplets can be harvested, achieving 100% IQE. The discovery and development of phosphorescent OLED contributed directly to the commercialization of active-matrix OLED (AMOLED) due to its high efficiency. Recently, Adachi achieved high efficiency through thermally activated delayed fluorescence (TADF) of organic compounds. These emitters have small singlet-triplet gap that makes the transition from triplet back to singlet possible. In the TADF device, the triplet excitons can go through reverse intersystem crossing to generate singlet excitons, resulting in high IQE. 
     OLEDs can also be classified as small molecule and polymer OLEDs according to the forms of the materials used. Small molecule refers to any organic or organometallic material that is not a polymer. The molecular weight of a small molecule can be large as long as it has well defined structure. Dendrimers with well-defined structures are considered as small molecules. Polymer OLEDs include conjugated polymers and non-conjugated polymers with pendant emitting groups. Small molecule OLED can become a polymer OLED if post polymerization occurred during the fabrication process. 
     There are various methods for OLED fabrication. Small molecule OLEDs are generally fabricated by vacuum thermal evaporation. Polymer OLEDs are fabricated by solution process such as spin-coating, inkjet printing, and slit printing. If the material can be dissolved or dispersed in a solvent, the small molecule OLED can also be produced by solution process. 
     The emitting color of an OLED can be achieved by emitter structural design. An OLED may comprise one emitting layer or a plurality of emitting layers to achieve desired spectrum. In the case of green, yellow, and red OLEDs, phosphorescent emitters have successfully reached commercialization. Blue phosphorescent emitters still suffer from non-saturated blue color, short device lifetime, and high operating voltage. Commercial full-color OLED displays normally adopt a hybrid strategy, using fluorescent blue and phosphorescent yellow, or red and green. At present, efficiency roll-off of phosphorescent OLEDs at high brightness remains a problem. In addition, it is desirable to have more saturated emitting color, higher efficiency, and longer device lifetime. 
     Metal complex compounds have been used in phosphorescent OLEDs, but their performance needs further improvement, such as color saturation and so on. The present application provides a series of new metal complexes containing heterocycle-substituted ligands. It has been found through studies that the introduction of six-membered electron deficient heterocyclic substitution brings the desired color shift. The application of these compounds as emitters in OLED devices can obtain the desired deep red color and near infrared luminescence. 
     3 SUMMARY OF THE INVENTION 
     The present invention aims to provide a series of new metal complexes containing heterocycle-substituted ligands to solve the above problems. The metal complexes can be used as emitters in an emissive layer of an electroluminescent device. These compounds can obtain deep red and near infrared luminescence. 
     According to an embodiment of the present invention, a metal complex comprising a ligand L a  represented by one of Formula 1 to 5 is disclosed: 
     
       
         
         
             
             
         
       
     
     wherein 
     X is selected from the group consisting of O, S, and Se; 
     R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8  and R 9  are each independently selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     At least one of R 1  to R 5  is represented by Formula 6: 
     
       
         
         
             
             
         
       
     
     wherein 
     X 1 , X 2 , X 3 , X 4  and X 5  are each independently selected from CR or N; and at least one of X 1 , X 2 , X 3 , X 4  and X 5  is N; 
     R is selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     R can be the same or different. 
     According to another embodiment of the present invention, an electroluminescent device is disclosed, which comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode, wherein comprising a meal complex comprising a ligand L a  represented by one of Formula 1 to 5: 
     
       
         
         
             
             
         
       
     
     wherein 
     X is selected from the group consisting of O, S, and Se; 
     R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8  and R9 are each independently selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     At least one of R 1  to R 5  is represented by Formula 6: 
     
       
         
         
             
             
         
       
     
     Wherein 
     X 1 , X 2 , X 3 , X 4  and X 5  are each independently selected from CR or N; and at least one of X 1 , X 2 , X 3 , X 4  and X 5  is N; 
     R is selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     R can be the same or different. 
     According to yet another embodiment of the present invention, a formulation comprising the metal complex is also disclosed. The metal complex comprises a ligand La represented by one of Formula 1 to 5. 
     The metal complex disclosed in the present invention has a heterocycle substituted ligand and can be used as emitters in the emissive layer of an organic electroluminescent device. The application of these novel compounds as emitters in phosphorescent OLED devices enables to obtain deep red and near infrared colors. 
    
    
     
       4 BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows an organic light emitting device that can incorporate the metal complex and the formulation disclosed herein. 
         FIG. 2  schematically shows another organic light emitting device that can incorporate the metal complex and the formulation disclosed herein. 
         FIG. 3  shows the Formula 1 of a ligand L a  contained in the metal complexd disclosed herein. 
         FIG. 4  shows the Formula 2 of a ligand L a  contained in the metal complexd disclosed herein. 
         FIG. 5  shows the Formula 3 of a ligand L a  contained in the metal complexd disclosed herein. 
         FIG. 6  shows the Formula 4 of a ligand L a  contained in the metal complexd disclosed herein. 
         FIG. 7  shows the Formula 5 of a ligand L a  contained in the metal complexd disclosed herein. 
     
    
    
     5 DETAILED DESCRIPTION 
     OLEDs can be fabricated on various types of substrates such as glass, plastic, and metal foil.  FIG. 1  schematically shows the organic light emitting device  100  without limitation. The figures are not necessarily drawn to scale. Some of the layer in the figure can also be omitted as needed. Device  100  may include a substrate  101 , an anode  110 , a hole injection layer  120 , a hole transport layer  130 , an electron blocking layer  140 , an emissive layer  150 , a hole blocking layer  160 , an electron transport layer  170 , an electron injection layer  180  and a cathode  190 . Device  100  may be fabricated by depositing the layers described in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference in its entirety. 
     More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. 
     The layered structure described above is provided by way of non-limiting example. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely. It may also include other layers not specifically described. Within each layer, a single material or a mixture of multiple materials can be used to achieve optimum performance. Any functional layer may include several sublayers. For example, the emissive layer may have a two layers of different emitting materials to achieve desired emission spectrum. Also for example, the hole transporting layer may comprise the first hole transporting layer and the second hole transporting layer. 
     In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer or multiple layers. 
     An OLED can be encapsulated by a barrier layer to protect it from harmful species from the environment such as moisture and oxygen.  FIG. 2  schematically shows the organic light emitting device  200  without limitation.  FIG. 2  differs from  FIG. 1  in that the organic light emitting device  200  include a barrier layer  102 , which is above the cathode  190 . Any material that can provide the barrier function can be used as the barrier layer such as glass and organic-inorganic hybrid layers. The barrier layer should be placed directly or indirectly outside of the OLED device. Multilayer thin film encapsulation was described in U.S. Pat. No. 7,968,146, which is herein incorporated by reference in its entirety. 
     Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. Some examples of such consumer products include flat panel displays, monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, smart phones, tablets, phablets, wearable devices, smart watches, laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles displays, and vehicle tail lights. 
     The materials and structures described herein may be used in other organic electronic devices listed above. 
     As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between. 
     As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form. 
     A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand. 
     It is believed that the internal quantum efficiency (IQE) of fluorescent OLEDs can exceed the 25% spin statistics limit through delayed fluorescence. As used herein, there are two types of delayed fluorescence, i.e. P-type delayed fluorescence and E-type delayed fluorescence. P-type delayed fluorescence is generated from triplet-triplet annihilation (TTA). 
     On the other hand, E-type delayed fluorescence does not rely on the collision of two triplets, but rather on the transition between the triplet states and the singlet excited states. Compounds that are capable of generating E-type delayed fluorescence are required to have very small singlet-triplet gaps to convert between energy states. Thermal energy can activate the transition from the triplet state back to the singlet state. This type of delayed fluorescence is also known as thermally activated delayed fluorescence (TADF). A distinctive feature of TADF is that the delayed component increases as temperature rises. If the reverse intersystem crossing rate is fast enough to minimize the non-radiative decay from the triplet state, the fraction of back populated singlet excited states can potentially reach 75%. The total singlet fraction can be 100%, far exceeding 25% of the spin statistics limit for electrically generated excitons. 
     E-type delayed fluorescence characteristics can be found in an exciplex system or in a single compound. Without being bound by theory, it is believed that E-type delayed fluorescence requires the luminescent material to have a small singlet-triplet energy gap (ΔE S-T ). Organic, non-metal containing, donor-acceptor luminescent materials may be able to achieve this. The emission in these materials is often characterized as a donor-acceptor charge-transfer (CT) type emission. The spatial separation of the HOMO and LUMO in these donor-acceptor type compounds often results in small ΔE S-T . These states may involve CT states. Often, donor-acceptor luminescent materials are constructed by connecting an electron donor moiety such as amino- or carbazole-derivatives and an electron acceptor moiety such as N-containing six-membered aromatic rings. 
     Definition of Terms of Substituents 
     halogen or halide—as used herein includes fluorine, chlorine, bromine, and iodine. 
     Alkyl—contemplates both straight and branched chain alkyl groups. Examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, neopentyl group, 1-methylpentyl group, 2-methylpentyl group, 1-pentylhexyl group, 1-butylpentyl group, 1-heptyloctyl group, 3-methylpentyl group. Additionally, the alkyl group may be optionally substituted. The carbons in the alkyl chain can be replaced by other hetero atoms.Of the above, preferred are methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butyl group, n-pentyl group, and neopentyl group. 
     Cycloalkyl—as used herein contemplates cyclic alkyl groups. Preferred cycloalkyl groups are those containing 4 to 10 ring carbon atoms and includes cyclobutyl, cyclopentyl, cyclohexyl, 4-methylcyclohexyl, 4,4-dimethylcylcohexyl, 1-adamantyl, 2-adamantyl, 1-norbornyl, 2-norbornyl and the like. Additionally, the cycloalkyl group may be optionally substituted. The carbons in the ring can be replaced by other hetero atoms. 
     Alkenyl—as used herein contemplates both straight and branched chain alkene groups. Preferred alkenyl groups are those containing two to fifteen carbon atoms. Examples of the alkenyl group include vinyl group, allyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 1,3-butandienyl group, 1-methylvinyl group, styryl group, 2,2-diphenylvinyl group, 1,2-diphenylvinyl group, 1-methylallyl group, 1,1-dimethylallyl group, 2-methylallyl group, 1-phenylallyl group, 2-phenylallyl group, 3-phenylallyl group, 3,3-diphenylallyl group, 1,2-dimethylallyl group, 1-phenyll-butenyl group, and 3-phenyl-1-butenyl group. Additionally, the alkenyl group may be optionally substituted. 
     Alkynyl—as used herein contemplates both straight and branched chain alkyne groups. Preferred alkynyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group may be optionally substituted. 
     Aryl or aromatic group—as used herein contemplates noncondensed and condensed systems. Preferred aryl groups are those containing six to sixty carbon atoms, preferably six to twenty carbon atoms, more preferably six to twelve carbon atoms. Examples of the aryl group include phenyl, biphenyl, terphenyl, triphenylene, tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene, preferably phenyl, biphenyl, terphenyl, triphenylene, fluorene, and naphthalene. Additionally, the aryl group may be optionally substituted. Examples of the non-condensed aryl group include phenyl group, biphenyl-2-yl group, biphenyl-3-yl group, biphenyl-4-yl group, p-terphenyl-4-yl group, p-terphenyl-3-yl group, p-terphenyl-2-yl group, m-terphenyl-4-yl group, m-terphenyl-3-yl group, m-terphenyl-2-yl group, o-tolyl group, m-tolyl group, p-tolyl group, p-t-butylphenyl group, p-(2-phenylpropyl)phenyl group, 4′-methylbiphenylyl group, 4″-t-butyl p-terphenyl-4-yl group, o-cumenyl group, m-cumenyl group, p-cumenyl group, 2,3-xylyl group, 3,4-xylyl group, 2,5-xylyl group, mesityl group, and m-quarterphenyl group. 
     Heterocyclic group or heterocycle—as used herein contemplates aromatic and non-aromatic cyclic groups. Hetero-aromatic also means heteroaryl. Preferred non-aromatic heterocyclic groups are those containing 3 to 7 ring atoms which includes at least one hetero atom such as nitrogen, oxygen, and sulfur. The heterocyclic group can also be an aromatic heterocyclic group having at least one heteroatom selected from nitrogen atom, oxygen atom, sulfur atom, and selenium atom. 
     Heteroaryl—as used herein contemplates noncondensed and condensed hetero-aromatic groups that may include from one to five heteroatoms. Preferred heteroaryl groups are those containing three to thirty carbon atoms, preferably three to twenty carbon atoms, more preferably three to twelve carbon atoms. Suitable heteroaryl groups include dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine, preferably dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, triazine, benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogs thereof. Additionally, the heteroaryl group may be optionally substituted. 
     Alkoxy—it is represented by —O-Alkyl. Examples and preferred examples thereof are the same as those described above. Examples of the alkoxy group having 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms include methoxy group, ethoxy group, propoxy group, butoxy group, pentyloxy group, and hexyloxy group. The alkoxy group having 3 or more carbon atoms may be linear, cyclic or branched. 
     Aryloxy—it is represented by —O-Aryl or —O-heteroaryl. Examples and preferred examples thereof are the same as those described above. Examples of the aryloxy group having 6 to 40 carbon atoms include phenoxy group and biphenyloxy group. 
     Arylalkyl—as used herein contemplates an alkyl group that has an aryl substituent. Additionally, the arylalkyl group may be optionally substituted. Examples of the arylalkyl group include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 1-phenylisopropyl group, 2-phenylisopropyl group, phenyl-t-butyl group, alpha.-naphthylmethyl group, 1-alpha.-naphthylethyl group, 2-alpha-naphthylethyl group, 1-alpha-naphthylisopropyl group, 2-alpha-naphthylisopropyl group, beta-naphthylmethyl group, 1-beta-naphthylethyl group, 2-beta-naphthylethyl group, 1-beta-naphthylisopropyl group, 2-beta-naphthylisopropyl group, p-methylbenzyl group, m-methylbenzyl group, o-methylbenzyl group, p-chlorobenzyl group, m-chlorobenzyl group, o-chlorobenzyl group, p-bromobenzyl group, m-bromobenzyl group, o-bromobenzyl group, p-iodobenzyl group, m-iodobenzyl group, o-iodobenzyl group, p-hydroxybenzyl group, m-hydroxybenzyl group, o-hydroxybenzyl group, p-aminobenzyl group, m-aminobenzyl group, o-aminobenzyl group, p-nitrobenzyl group, m-nitrobenzyl group, o-nitrobenzyl group, p-cyanobenzyl group, m-cyanobenzyl group, o-cyanobenzyl group, 1-hydroxy-2-phenylisopropyl group, and 1-chloro2-phenylisopropyl group. Of the above, preferred are benzyl group, p-cyanobenzyl group, m-cyanobenzyl group, o-cyanobenzyl group, 1-phenylethyl group, 2-phenylethyl group, 1-phenylisopropyl group, and 2-phenylisopropyl group. 
     The term “aza” in azadibenzofuran, aza-dibenzothiophene, etc. means that one or more of the C—H groups in the respective aromatic fragment are replaced by a nitrogen atom. For example, azatriphenylene encompasses dibenzo[f,h]quinoxaline,dibenzo[f,h]quinoline and other analogues with two or more nitrogens in the ring system. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein. 
     The alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic group, aryl, and heteroaryl may be unsubstituted or may be substituted with one or more substituents selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, an acyl group, a carbonyl group, a carboxylic acid group, an ether group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof. 
     It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or attached fragment are considered to be equivalent. 
     In the compounds mentioned in this disclosure, the hydrogen atoms can be partially or fully replaced by deuterium. Other atoms such as carbon and nitrogen, can also be replaced by their other stable isotopes. The replacement by other stable isotopes in the compounds may be preferred due to its enhancements of device efficiency and stability. 
     In the compounds mentioned in this disclosure, multiple substitutions refer to a range that includes a double substitution, up to the maximum available substitutions. 
     In the compounds mentioned in this disclosure, the expression that adjacent substituents are optionally joined to form a ring is intended to be taken to mean that two radicals are linked to each other by a chemical bond. This is illustrated by the following scheme: 
     
       
         
         
             
             
         
       
     
     Furthermore, the expression that adjacent substituents are optionally joined to form a ring is also intended to be taken to mean that in the case where one of the two radicals represents hydrogen, the adical is bonded at a positi e hydrogen atom was bonded, with formation This is illustrated by the f me: 
     
       
         
         
             
             
         
       
     
     According to an embodiment of the present invention, a metal complex is disclosed that comprises a ligand L a  represented by Formula 1, Formula 2, Formula 3, Formula 4 or Formula 5: 
     
       
         
         
             
             
         
       
     
     wherein 
     X is selected from the group consisting of O, S, and Se; 
     R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8  and R 9  are each independently selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     at least one of R 1  to R 5  is represented by Formula 6: 
     
       
         
         
             
             
         
       
     
     Wherein X 1 , X 2 , X 3 , X 4  and X 5  in Formula 6 are each independently selected from CR or N; and at least one of X 1 , X 2 , X 3 , X 4  and X 5  is N; 
     R is selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     R can be the same or different; 
     In this embodiment, it is obvious that the definition of “at least one of R 1  to R 5  is represented by Formula 6” is based on the substituents present in Formulas 1-5. For example, for Formula 3, which does not exist for R 5 , then should be “at least one of R 1  to R 4  is represented by Formula 6”. It is similarly in Formula 4 and Formula 5. That is, at least one of R 1  to R 3  in Formula 4 is represented by Formula 6, and at least one of R 1  to R 2  in Formula 5 is represented by Formula 6. 
     In this embodiment, X 1 , X 2 , X 3 , X 4  and X 5  in Formula 6 are each independently selected from CR or N. When more than one of X 1 , X 2 , X 3 , X 4  and X 5  are selected from CR, each R can be independently selected from the above range, and R can be the same or different. For example, X 1 , X 3  and X 5  are selected from N, and X 2  and X 4  are selected from CR, wherein R in X 2  and X 4  may both be methyl, or R in X 2  is methyl, and R in X 4  is ethyl. 
     According to another embodiment of the present invention, wherein the metal is selected from the group consisting of Cu, Ag, Au, Ru, Rh, Pd, Pt, Os and Ir. 
     According to another embodiment of the present invention, wherein the metal is selected from the group consisting of Pt and Ir. 
     According to another embodiment of the present invention, wherein one of R 1  to R 5  is selected from the group consisting of a substituted or unsubstituted pyridine group, a substituted or unsubstituted pyrimidine group, a substituted or unsubstituted pyrazine group, and a substituted or unsubstituted triazine group. 
     According to another embodiment of the present invention, wherein R, R 7  and R 9  are each independently selected from group consisting of hydrogen, deuterium, fluorine, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, and combinations thereof. 
     According to another embodiment of the present invention, wherein R, R 7  and R 9  are each independently selected from the group consisting of hydrogen, methyl, ethyl, isopropyl, isobutyl, neopentyl, cyclobutyl, cyclopentyl, cyclohexyl, 4,4-dimethylcyclohexyl, norbornyl, adamantyl, 3,3,3-trifluoropropyl, 3,3,3-trifluoro-2,2-dimethylpropyl, and each above deuterated group. 
     According to another embodiment of the present invention, wherein the complex has the formula of M(L a ) m (L b ) n (L c ) q , wherein L b  and L c  are the second and third ligand coordinating to M, L b  and L c  can be the same of different; 
     L a , L b  and L c  can be optionally joined to form a multidentate ligand; 
     Wherein m is 1, 2, or 3, n is 0, 1, or 2, q is 0, 1, or 2; m+n+q is the oxidation state of M; 
     Wherein L b  and L c  are independently selected from the group consisting of: 
     
       
         
         
             
             
         
       
     
     Wherein 
     R a , R b  and R c  can represent mono, di, tri, or tetra substitution or no substitution; 
     X b  is selected from the group consisting of O, S, Se, NR N1 , CR C1 R C2 ; 
     R a , R b , R c , R N1 , R C1  and R C2  are each independently selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group and combinations thereof; 
     Two adjacent substituents are optionally joined to form a ring. 
     According to another embodiment of the present invention, wherein the metal complex has the formula of Ir(L a ) 2 L b . 
     According to another preferred embodiment of the present invention, wherein L a  is anyone or any two selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     According to another preferred embodiment of the present invention, wherein the ligand L b  is selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     According to another embodiment of the present invention, wherein L a  and L b  can be partially or fully deuterated. 
     According to another embodiment of the present invention, the metal complex has the formula of Ir(L a ) 2 L b , wherein the ligand L b  is anyone selected from L b1  to L b373 , the ligand L a  is anyone or any two selected from the group consisting of L a1-1  to La 1-190 , L a2-1  to L a2-190 , L a1-1  to L a3-152 , L a4-1  to L a4-114 , and L a5-1  to L a5-228 . 
     According to another embodiment of the present invention, an organic electroluminescent device is disclosed. The electroluminescent device comprises: 
     an anode, 
     a cathode, 
     and an organic layer, disposed between the anode and the cathode, comprising a meal complex comprising a ligand L a  represented by one of Formula 1 to 5: 
     
       
         
         
             
             
         
       
     
     Wherein 
     X is selected from the group consisting of O, S, and Se; 
     R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8  and R 9  are each independently selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     at least one of R 1  to R 5  is represented by Formula 6: 
     
       
         
         
             
             
         
       
     
     Wherein X 1 , X 2 , X 3 , X 4  and X 5  in Formula 6 are each independently selected from CR or N; and at least one of X 1 , X 2 , X 3 , X 4  and X 5  is N; 
     R is selected from the group consisting of hydrogen, deuterium, halogen, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 ring carbon atoms, a substituted or unsubstituted heteroalkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted arylalkyl group having 7 to 30 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 30 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 30 carbon atoms, a substituted or unsubstituted alkylsilyl group having 3 to 20 carbon atoms, a substituted or unsubstituted arylsilyl group having 6 to 20 carbon atoms, a substituted or unsubstituted amino group having 0 to 20 carbon atoms, an acyl group, a carbonyl group, a carboxylic acid group, an ester group, a nitrile group, an isonitrile group, a sulfanyl group, a sulfinyl group, a sulfonyl group, a phosphino group, and combinations thereof; 
     R can be the same or different. 
     In one embodiment, wherein the organic layer is the emissive layer and the metal complex is the emitter. 
     In one embodiment, wherein the device emits light from red to near infrared. 
     In one embodiment, wherein the device emits white light. 
     In one embodiment, wherein the organic layer further comprises a host compound. 
     In one embodiment, wherein the host compound comprises at least on the chemical groups selected from the group consisting of carbazole, azacarbazole, indolocarbazole, dibenzothiophene, dibenzofuran, triphenylene, naphthalene, phenanthrene, triazine, quinazoline, quinoxaline, azadibenzothiophene, azadibenzofuran and the combinations thereof. 
     According to yet another embodiment, a formulation comprising the metal complex is also disclosed. The specific structure of the metal complex is described in any of the above embodiments. 
     Combination with Other Materials 
     The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. The combinations of these materials are described in more detail in U.S. Pat. App. No. 20160359122 at paragraphs 0132-0161, which are incorporated by reference in its entirety. The materials described or referred to the disclosure are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination. 
     The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in combination with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The combination of these materials is described in detail in paragraphs 0080-0101 of U.S. Pat. App. No. 20150349273, which are incorporated by reference in its entirety. The materials described or referred to the disclosure are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination. 
     In the embodiments of material synthesis, all reactions were performed under nitrogen protection unless otherwise stated. All reaction solvents were anhydrous and used as received from commercial sources. Synthetic products were structurally confirmed and tested for properties using one or more conventional equipment in the art (including, but not limited to, nuclear magnetic resonance instrument produced by BRUKER, liquid chromatograph produced by SHIMADZU, liquid chromatography-mass spectrometer produced by SHIMADZU, gas chromatography-mass spectrometer produced by SHIMADZU, differential Scanning calorimeters produced by SHIMADZU, fluorescence spectrophotometer produced by SHANGHAI LENGGUANG TECH., electrochemical workstation produced by WUHAN CORRTEST, and sublimation apparatus produced by ANHUI BEQ, etc.) by methods well known to the persons skilled in the art. In the embodiments of the device, the characteristics of the device were also tested using conventional equipment in the art (including, but not limited to, evaporator produced by ANGSTROM ENGINEERING, optical testing system produced by SUZHOU FATAR, life testing system produced by SUZHOU FATAR, and ellipsometer produced by BEIJING ELLITOP, etc.) by methods well known to the persons skilled in the art. As the persons skilled in the art are aware of the above-mentioned equipment use, test methods and other related contents, the inherent data of the sample can be obtained with certainty and without influence, so the above related contents are not further described in this patent. 
     SYNTHESIS EXAMPLES 
     The method for preparing the compounds of the present invention is not limited. The following compounds are exemplified as a typical but non-limiting example, and the synthesis route and preparation method are as follows: 
     Synthesis Example 1 
     Synthesis of Compound Ir(L a1-37 ) 2 L b106    
     Step 1: Synthesis of Intermediate 1 
     
       
         
         
             
             
         
       
     
     To a 1 L round bottom flask were added 2,4-dichloroquinoline (15 g, 75.7 mmol), 3,5-dimethylphenyl boronic acid (11.4 g, 75.7 mmol), Pd(PPh 3 ) 4  (4.37 g, 3.8 mmol), sodium carbonate (12 g, 113.6 mmol), 1,4-dioxane (300 mL) and water (75 mL). Then the mixture was bubbled with N 2  for 5 min. Then the reaction was heated to reflux overnight under the protection of N 2 . After the finish of the reaction shown by TLC, the mixture was cooled to room temperature, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with ethyl acetate:PE=1:100 (v:v), afforded a crude product (18 g) as a white solid. Then recrystallization from n-hexane afforded the intermediate 1 (10.3 g, 51% yield) as a white crystal. 
     Step 2: Synthesis of Intermediate 2 
     
       
         
         
             
             
         
       
     
     To a 250 mL round bottom flask were added intermediate 1 (10 g, 37.4 mmol), bis(pinacolato)diboron (11.4 g, 44.8 mmol), Pd(OAc) 2  (420 mg, 1.9 mmol), Sphos (1.5 g, 3.7 mmol), potassium acetate (5.5 g, 56.2 mmol) and 1,4-dioxane (150 mL). Then the mixture was bubbled with N 2  for 5 min. Then the reaction was heated to reflux overnight under the protection of N 2 . After the finish of the reaction shown by TLC, the mixture was cooled to room temperature, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with ethyl acetate:PE=1:10 (v:v), afforded a crude product (10.3 g) as a white solid. Then recrystallization from n-hexane afforded the intermediate 2 (8.2 g, 61% yield) as a white powder. 
     Step 3: Synthesis of Intermediate 3 
     
       
         
         
             
             
         
       
     
     To a 250 mL round bottom flask were added cyanuric chloride (13.1 g, 70.8 mmol), CuI (458 mg, 2.4 mmol) and super dry THF (50 mL). Then the mixture was bubbled with N 2  for 5 min. Then the reaction was cooled to 0° C. and to which was added tert-butyl chloride magnesium (100 mL, 170 mmol) dropwise, and after addition the reaction was warmed to room temperature and stirred overnight. After the finish of the reaction shown by TLC, the mixture was quenched by carefully addition of saturated ammonium chloride solution, and then ethyl acetate was added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with PE, afforded the intermediate 3 (11.2 g, 69% yield) as a white powder. 
     Step 4: Synthesis of Intermediate 4 
     
       
         
         
             
             
         
       
     
     To 250 mL round bottom flask were added intermediate 3 (3.74 g, 16.4 mmol), intermediate 2 (6.2 g, 17.3 mmol), Pd(PPh 3 ) 4  (948 mg, 0.82 mmol), potassium carbonate (3.4 g, 24.6 mmol), 1,4-dioxane (60 mL) and water (15 mL), and then the resulting mixture was bubbled with N 2  for 5 min. Then the reaction was heated to reflux overnight under the protection of N 2 . After the finish of the reaction shown by TLC, the mixture was cooled to room temperature, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with ethyl acetate: PE=1:200 (v:v), afforded a crude product (6.7 g) as a white solid. Then recrystallization from ethanol afforded the intermediate 4 (5.2 g, 75% yield) as a white crystal. 
     Step 5: Synthesis of Iridium Dimer 
     
       
         
         
             
             
         
       
     
     To 100 mL round bottom flask were added intermediate 4 (3 g, 7.1 mmol), iridium (III) chloride trihydrate (498 mg, 1.4 mmol), ethoxyethanol (15 mL) and water (5 mL), and then the resulting mixture was bubbled with N 2  for 3 min, and then the reaction was heated to reflux overnight under the protection of N 2 , the color of the reaction changed from yellow green to black. Then the reaction was cooled to room temperature, and the water wherein was evaporated, and the resulting solution of the dimer in ethoxyethanol was directly used in the next step without further purification. 
     Step 6: Synthesis of Compound Ir(L a1-37 ) 2 L b106    
     
       
         
         
             
             
         
       
     
     The mixture of the iridium dimer (0.7 mmol) obtained in step 5, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (673 mg, 2.8 mmol), potassium carbonate (967 mg, 7 mmol), and 2-ethoxyethanol (20 mL) was stirred at room temperature under N 2  for 24 h. After the finish of the reation shown by HPLC, celite was added to the funnel and the reaction mixture was poured to the celite, filtered, the filter cake was washed with ethanol for several times, and then the product in the filter cake was washed off to the solution, and then to the solution was added a certain amount of ethanol, and DCM therein was carefully evaporated on a rotary evaporation machine, black solid precipitated from the solution, filtered, the resulting solid was washed with ethanol for several times, pumped to dryness and afforded compound Ir(L a1-37 ) 2 L b106  (1.32 g, 73% yield) as a black solid. The product was confirmed as the target product, with a molecular weight of 1279. 
     Synthesis Example 2 
     Synthesis of Compound Ir(L a3-113 ) 2 L b106    
     Step1: Synthesis of Intermediate 5 
     
       
         
         
             
             
         
       
     
     To 250 mL round bottom flask was added 6-bromo-1-(3,5-dimethylphenyl)isoquinoline (10 g, 32 mmol), and then 60 mL of super dry THF and stirred to dissolve. Then the resulting solution was bubbled with N 2  for 5 min, and cooled to −72° C. Then to the solution was added a n-BuLi solution in n-hexane (14 mL, 35.2 mmol) dropwise under the protection of N 2 , and the reaction was kept at the same temperature for 30 min after the dropwise addition, and then isopropoxyboronic acid pinacol ester (7.14 g, 38.4 mmol) was added, and the reaction was slowly warmed to room temperature and stirred overnight. Then the reaction was quenched by the addition of saturated ammonium chloride solution, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness to afford a crude product as a yellow solid, which was recrystallized from n-hexane to afford the intermediate 5 (7 g, 61% yield) as a gray white powder. 
     Step 2: Synthesis of Intermediate 6 
     
       
         
         
             
             
         
       
     
     To 250 mL round bottom flask were added intermediate 3 (3.62 g, 15.9 mmol), intermediate 5 (6 g, 16.7 mmol), Pd(PPh 3 ) 4  (919 mg, 0.8 mmol), potassium carbonate (3.3 g, 23.9 mmol), 1,4-dioxane (60 mL) and water (15 mL), and the resulting mixture was bubbled with N 2  for 5 min. Then the reaction was heated to reflux overnight under the protection of N 2 . After the finish of the reaction shown by TLC, the mixture was cooled to room temperature, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with ethyl acetate:PE=1:30 (v:v), afforded the intermediate 6 (5.8 g, 86% yield) as a white solid. 
     Step 3: Synthesis of Iridium Dimer 
     
       
         
         
             
             
         
       
     
     To 100 mL round bottom flask were added intermediate 6 (3 g, 7.1 mmol), iridium (III) chloride trihydrate (498 mg, 1.4 mmol), ethoxyethanol (15 mL) and water (5 mL), and then the resulting mixture was bubbled with N 2  for 3 min, and then the reaction was heated to reflux overnight under the protection of N 2 , the color of the reaction changed from yellow green to black. Then the reaction was cooled to room temperature, and the water wherein was evaporated, and the resulting solution of the dimer in ethoxyethanol was directly used in the next step without further purification. 
     Step 4: Synthesis of Compound Ir(L a3-113 ) 2 L b106    
     
       
         
         
             
             
         
       
     
     The mixture of the iridium dimer (0.7 mmol) obtained in the front step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (673 mg, 2.8 mmol), potassium carbonate (967 mg, 7 mmol), and 2-ethoxyethanol (20 mL) was stirred at room temperature under N 2  for 24 h. After the finish of the reation shown by HPLC, celite was added to the funnel and the reaction mixture was poured to the celite, filtered, the filter cake was washed with ethanol for several times, and then the product in the filter cake was washed off with DCM to the solution, and then to the solution was added a certain amount of ethanol, and DCM therein was carefully evaporated on a rotary evaporation machine, and a black solid precipitated from the solution, filtered, and the resulting solid was washed with ethanol for several times, pumped to dryness and afforded Compound Ir(L a3-113 ) 2 L b106  (1.4 g, 77% yield) as a black solid. The product was confirmed as the target product, with a molecular weight of 1279. 
     Synthesis Example 3 
     Synthesis of Compound Ir(L a4-75 ) 2 L b106    
     Step 1: Synthesis of Intermediate 7 
     
       
         
         
             
             
         
       
     
     To a 500 mL round bottom flask were added 4,7-dichloroquinazoline (11 g, 55.3 mmol), 3,5-dimethylphenyl boronic acid (8.7 g, 58.0 mmol), Pd(PPh 3 ) 4  (3.2 g, 2.3 mmol), sodium carbonate (8.8 g, 82.9 mmol), 1,4-dioxane (150 mL) and water (50 mL). And then the resulting mixture was bubbled with N 2  for 5 min, and then the reaction was heated to reflux overnight under the protection of N 2 . After the finish of the reaction shown by TLC, the mixture was cooled to room temperature, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with ethyl acetate:PE=1:50 (v:v), afforded intermediate 7 (10.3 g, 51% yield) as a white solid. 
     Step 2: Synthesis of Intermediate 8 
     
       
         
         
             
             
         
       
     
     To a 500 mL round bottom flask were added intermediate 7 (5.7 g, 21.2 mmol), bis(pinacolato)diboron (6.5 g, 25.5 mmol), Pd(OAc) 2  (238 mg, 1.1 mmol), Sphos (870 mg, 2.1 mmol), potassium acetate (3.1 g, 31.9 mmol) and 1,4-dioxane (210 mL). Then the mixture was bubbled with N 2  for 5 min. Then the reaction was heated to reflux overnight under the protection of N 2 . After the finish of the reaction shown by TLC, the mixture was cooled to room temperature, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with ethyl acetate:PE=1:10 (v:v), afforded the intermediate 8 (6.1 g, 81% yield) as a white powder. 
     Step 3: Synthesis of Intermediate 9 
     
       
         
         
             
             
         
       
     
     To 50 mL round bottom flask were added intermediate 3 (438 mg, 1.9 mmol), intermediate 8 (730 mg, 2.0 mmol), Pd(PPh 3 ) 4  (111 mg, 0.1 mmol), potassium carbonate (0.4 g, 2.9 mmol), 1,4-dioxane (8 mL) and water (2 mL), and the resulting mixture was bubbled with N 2  for 5 min. Then the reaction was heated to reflux overnight under the protection of N 2 . After the finish of the reaction shown by TLC, the mixture was cooled to room temperature, and then water and ethyl acetate were added, extracted, and the organic phase was combined, dried over MgSO 4  and evaporated to dryness, purified via silica gel column chromatography, eluting with ethyl acetate:PE=1:50 (v:v), afforded the intermediate 9 (747 mg, 87% yield) as a white solid. 
     Step 4: Synthesis of Iridium Dimer 
     
       
         
         
             
             
         
       
     
     To 50 mL round bottom flask were added intermediate 9 (747 mg, 1.8 mmol), iridium (III) chloride trihydrate (127 mg, 0.36 mmol), ethoxyethanol (6 mL) and water (2 mL), and then the resulting mixture was bubbled with N 2  for 3 min, and then the reaction was heated to reflux overnight under the protection of N 2 , the color of the reaction changed from yellow green to black. Then the reaction was cooled to room temperature, and the water wherein was evaporated, and the resulting solution of the dimer in ethoxyethanol was directly used in the next step without further purification. 
     Step 5: Synthesis of Compound Ir(L a4-75 ) 2 L b106    
     
       
         
         
             
             
         
       
     
     The mixture of the iridium dimer (0.18 mmol) obtained in the front step, 3,7-diethyl-3,7-dimethylnonane-4,6-dione (173 mg, 0.72 mmol), potassium carbonate (249 mg, 1.8 mmol), and 2-ethoxyethanol (8 mL) was stirred at room temperature under N 2  for 24 h. After the finish of the reation shown by HPLC, celite was added to the funnel and the reaction mixture was poured to the celite, filtered, the filter cake was washed with ethanol for several times, and then the product in the filter cake was washed off with DCM to the solution, and then to the solution was added a certain amount of ethanol, and DCM therein was carefully evaporated on a rotary evaporation machine, and a black solid precipitated from the solution, filtered, the resulting solid was washed with ethanol for several times, pumped to dryness and afforded Compound Ir(L a4-75 ) 2 L b106  (185 mg, 60% yield) as a black solid. The product was confirmed as the target product, with a molecular weight of 1281. 
     The persons skilled in the art should know that the above preparation method is only an illustrative example, and the persons skilled in the art can obtain the structure of other compounds of the present invention by modifying the above preparation method. 
     The wavelength of the compounds from the synthesis examples were measured with a fluorescent spectrophotometer, and the maximum emission wavelength (λmax) and the full width of half maximum (FWHM) obtained were shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Maximum emission wavelength and full width 
               
               
                 of half maximum of each compound 
               
            
           
           
               
               
               
               
            
               
                 Compound 
                 Ir(L a1-37 ) 2 L b106   
                 Ir(L a3-113 ) 2 L b106   
                 Ir(L a4-75 ) 2 L b106   
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 λmax (nm) 
                 738 
                 681 
                 709 
               
               
                 FWHM(nm) 
                 81.35 
                 45.54 
                 47.93 
               
               
                   
               
            
           
         
       
     
     Device Example 1 
     A glass substrate with 120 nm thick indium-tin-oxide (ITO) anode was first cleaned and then treated with oxygen plasma and UV ozone. After the treatments, the substrate was baked dry in a glovebox to remove moisture. The substrate was then mounted on a substrate holder and loaded into a vacuum chamber. The organic layers specified below were deposited in sequence by thermal vacuum deposition on the ITO anode at a rate of 0.2-2 Å/s at a vacuum of around 10 −8  torr. Compound HI (100 Å) was used as the hole injection layer (HIL). Compound HT (400 Å) was used as the hole transporting layer (HTL). Then Compound EB (50 Å) was used as the electron blocking layer (EBL). Compound Ir(L a1-37 ) 2 L b106  of the present invention was doped in the host Compound H as the emitting layer (EML, 400 Å). Compound HB (50 Å) was deposited as the hole blocking layer (HBL). On the HBL, a mixture of Compound ET and 8-quinolinolato-lithium (Liq) (35:65, 350 Å) was deposited as the electron transporting layer (ETL). Finally, 10 Å-thick Liq was deposited as the electron injection layer and 1200 Å of Al was deposited as the cathode. The device was then transferred back to the glovebox and encapsulated with a glass lid and a moisture getter to complete the device. 
     The detailed device layer structure and thicknesses are shown in Table 2 below. In the layers in which more than one material were used, they were obtained by doping different compounds in the weight ratios described therein: 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Device structure of Device Example 
               
            
           
           
               
               
            
               
                   
                 Device ID 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 HIL 
                 HTL 
                 EBL 
                 EML 
                 HBL 
                 ETL 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Device 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
                 Compound 
               
               
                 Example 1 
                 HI 
                 HT 
                 EB 
                 H:Compound 
                 HB 
                 ET:Liq 
               
               
                   
                 (100 Å) 
                 (400 Å) 
                 (50 Å) 
                 Ir(L a1-37 ) 2 L b106   
                 (50 Å) 
                 (35:65) 
               
               
                   
                   
                   
                   
                 (95:5) 
                   
                 (350 Å) 
               
               
                   
                   
                   
                   
                 (400 Å) 
               
               
                   
               
            
           
         
       
     
     Structure of the materials used in the devices are shown as below: 
     
       
         
         
             
             
         
       
     
     The λmax, full width at half maximum (FWHM), and voltage (V) were measured at a current density of 15 mA/cm 2 . The sublimation temperature (Sub T) of the compound of the invention was also recorded in table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Device data 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Sub T 
                 λmax 
                 FWHM 
                 Voltage 
               
               
                   
                 Device ID 
                 (° C.) 
                 (nm) 
                 (nm) 
                 (V) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Device Example 1 
                 250 
                 731 
                 98.5 
                 4.69 
               
               
                   
                   
               
            
           
         
       
     
     Discussion: 
     The data in table 3 show that the device example using the compound of the present invention has a near infrared λmax of 731 nm and can be used as a near-infrared OLED material. And, from the data shown in table 1, the use of different ligand L a  can effectively control the emissive wavelength during the area between deep red and near infrared and the peak width, to meet the need of business application. For example, in some applications, it is necessary for the devices to emit only near infrared light but none of visible light, and in some other applications, it is necessary for the devices to emit very saturated and extremely deep red light, and the emissive wavelength and narrow peak width of the compounds of the present invention can meet these requirements. 
     It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. Many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. It is understood that various theories as to why the invention works are not intended to be limiting.