Patent Publication Number: US-11653558-B2

Title: Organic electroluminescent materials and devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/450,865, filed Aug. 4, 2014, which is a non-provisional of U.S. Provisional Application No. 61/916,552, filed Dec. 16, 2013. The disclosure of which is incorporated by reference in its entirety. 
    
    
     JOINT RESEARCH AGREEMENT 
     The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement. 
     FIELD OF THE INVENTION 
     The present invention relates to novel iridium complexes that can be used in organic light emitting devices (OLEDs). The present invention relates to the iridium complexes, devices comprising the iridium complexes, and formulations comprising the iridium complexes. 
     BACKGROUND 
     Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices, organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants. 
     OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety. 
     One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art. 
     One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy) 3 , which has the following structure: 
     
       
         
         
             
             
         
       
     
     In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line. 
     As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules. 
     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 processable” 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. 
     As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level. 
     As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions. 
     More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety. 
     BRIEF SUMMARY OF THE INVENTION 
     A new class of heteroleptic Ir(III) complexes are provided. 
     The present invention provides compounds of formula I:
 
(L A ) m Ir(B) 3-m   (I).
 
In the compound of formula I, L A  is
 
                         
L B  is selected from the group consisting of:
 
                         
R E  represents mono or di-substitution, or no substitution; R 2 , R A , and R D  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R B , R C , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; X is selected from the group consisting of O, S, and Se; R 1 , R 2 , R A , R B , R C , R D , R E , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, m is 2. 
     In some embodiments, X is O. 
     In some embodiments, R 3  is an alkyl having at least 2 carbons. 
     In some embodiments, R 3  is an alkyl having at least 3 carbons. 
     In some embodiments, R 3  is a cycloalkyl. 
     In some embodiments, R 3  is selected from the group consisting of methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, cyclopentyl, and cyclohexyl, wherein each is optionally partially or fully deuterated. 
     In some embodiments, R 1  is selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, and combinations thereof. 
     In some embodiments, R 2  represents no substitution. 
     In some embodiments, R F  is selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, halogen, and combinations thereof. In some embodiments, R F  is fluorine. 
     In some embodiments, R C , R D , and R E  each represent no substitution. 
     In some embodiments, L B  is selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, L B  is: 
                         
wherein R G  represents mono, di, tri, or tetra-substitution, or no substitution; and wherein R G  is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 
     In some embodiments wherein L B  is formula VI, R B  and R E  represent no substitution; and R F  and R G  are each independently selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, halogen, and combinations thereof. In some embodiments wherein L B  is formula VI, R G  is fluorine. 
     In some embodiments, L A  is selected from the group consisting of L A1  to L A86 . 
     In some embodiments, L B  is selected from the group consisting of L B1  to L B259 . 
     In some embodiments, the compound of formula I is selected from the group consisting of Compound I-1 to Compound I-15. 
     In some embodiments, a first device is provided. The first device comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula:
 
(L A ) m Ir(L B ) 3-m   (I).
 
In the compound of formula I, L A  is
 
                         
L B  is selected from the group consisting of:
 
                         
R E  represents mono or di-substitution, or no substitution; R 2 , R A , and R D  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R B , R C , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; X is selected from the group consisting of O, S, and Se; R 1 , R 2 , R A , R B , R C , R D , R E , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, the first device is a consumer product. 
     In some embodiments, the first device is an organic light-emitting device. 
     In some embodiments, the first device comprises a lighting panel. 
     In some embodiments, the organic layer of the first device is an emissive layer and the compound is an emissive dopant. In some embodiments, the organic layer of the first device is an emissive layer and the compound is a non-emissive dopant. 
     In some embodiments, the organic layer of the first device further comprises a host. 
     In some embodiments, the host of the first device comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan; wherein any substituent in the host is an unfused substituent independently selected from the group consisting of C n H 2n+1 , OC n H 2n+1 , OAr 1 , N(C n H 2n+1 ) 2 , N(Ar 1 )(Ar 2 ), CH═CH—C n H 2n+1 , C≡CC n H 2n+1 , Ar 1 , Ar 1 —Ar 2 , C n H 2n —Ar 1 , or no substitution; wherein n is from 1 to 10; and wherein Ar 1  and Ar 2  are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof. 
     In some embodiments, the host of the first device comprises at least one chemical group selected from the group consisting of carbazole, dibenzothiophene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene. 
     In some embodiments, the host is selected from the group consisting of: 
                                           
and combinations thereof.
 
     In some embodiments, the host of the first device comprises a metal complex. 
     In some embodiments, a formulation comprising a compound of formula I is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
         FIG.  1    shows an organic light emitting device. 
         FIG.  2    shows an inverted organic light emitting device that does not have a separate electron transport layer. 
         FIG.  3    shows a compound of Formula I-A. 
         FIG.  4    shows a compound of Formula I-B. 
         FIG.  5    shows a compound of Formula I-C. 
     
    
    
     DETAILED DESCRIPTION 
     Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable. 
     The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds. 
     More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference. 
       FIG.  1    shows an organic light emitting device  100 . The figures are not necessarily drawn to scale. Device  100  may include a substrate  110 , an anode  115 , a hole injection layer  120 , a hole transport layer  125 , an electron blocking layer  130 , an emissive layer  135 , a hole blocking layer  140 , an electron transport layer  145 , an electron injection layer  150 , a protective layer  155 , a cathode  160 , and a barrier layer  170 . Cathode  160  is a compound cathode having a first conductive layer  162  and a second conductive layer  164 . 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. 
     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 F 4 -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 emissive and 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. 
       FIG.  2    shows an inverted OLED  200 . The device includes a substrate  210 , a cathode  215 , an emissive layer  220 , a hole transport layer  225 , and an anode  230 . Device  200  may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device  200  has cathode  215  disposed under anode  230 , device  200  may be referred to as an “inverted” OLED. Materials similar to those described with respect to device  100  may be used in the corresponding layers of device  200 .  FIG.  2    provides one example of how some layers may be omitted from the structure of device  100 . 
     The simple layered structure illustrated in  FIGS.  1  and  2    is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device  200 , hole transport layer  225  transports holes and injects holes into emissive layer  220 , and may be described as a hole transport layer or a hole injection layer. In some embodiments, 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 may further comprise multiple layers of different organic materials as described, for example, with respect to  FIGS.  1  and  2   . 
     Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in  FIGS.  1  and  2   . For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties. 
     Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. Pat. No. 7,431,968, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJP. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processability than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing. 
     Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material as described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material consists essentially of polymeric silicon and inorganic silicon. 
     Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, 3-D displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.), but could be used outside this temperature range, for example, from −40 degree C. to +80 degrees C. 
     The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures. 
     The term “halo” or “halogen” as used herein includes fluorine, chlorine, bromine and iodine. 
     The term “alkyl” as used herein contemplates both straight and branched chain alkyl radicals. Preferred alkyl groups are those containing from one to fifteen carbon atoms and includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, and the like. Additionally, the alkyl group may be optionally substituted. 
     The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals. Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms and includes cyclopropyl, cyclopentyl, cyclohexyl, and the like. Additionally, the cycloalkyl group may be optionally substituted. 
     The term “alkenyl” as used herein contemplates both straight and branched chain alkene radicals. Preferred alkenyl groups are those containing two to fifteen carbon atoms. Additionally, the alkenyl group may be optionally substituted. 
     The term “alkynyl” as used herein contemplates both straight and branched chain alkyne radicals. Preferred alkyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group may be optionally substituted. 
     The terms “aralkyl” or “arylalkyl” as used herein contemplates an alkyl group that has as a substituent an aromatic group. Additionally, the aralkyl group may be optionally substituted. 
     The term “heterocyclic group” as used herein contemplates non-aromatic cyclic radicals. Preferred heterocyclic groups are those containing 3 or 7 ring atoms which includes at least one hetero atom, and includes cyclic amines such as morpholino, piperdino, pyrrolidino, and the like, and cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and the like. Additionally, the heterocyclic group may be optionally substituted. 
     The term “aryl” or “aromatic group” as used herein contemplates single-ring groups and polycyclic ring systems. The polycyclic rings may have two or more rings in which two carbons are common by two adjoining rings (the rings are “fused”) wherein at least one of the rings is aromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles and/or heteroaryls. Additionally, the aryl group may be optionally substituted. 
     The term “heteroaryl” as used herein contemplates single-ring hetero-aromatic groups that may include from one to three heteroatoms, for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine and pyrimidine, and the like. The term heteroaryl also includes polycyclic hetero-aromatic systems having two or more rings in which two atoms are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is a heteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles and/or heteroaryls. Additionally, the heteroaryl group may be optionally substituted. 
     The alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic group, aryl, and heteroaryl may be optionally substituted with one or more substituents selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. 
     As used herein, the term “substituted” indicates that a substituent other than hydrogen is bonded to the relevant carbon or nitrogen atom. Thus, where R 1  is mono-substituted, then one R 1  must be other than hydrogen. Similarly, where R 1  is di-substituted, then two of R 1  must be other than hydrogen. Similarly, where R 1  “represents no substitution,” R 1  is hydrogen for all available positions. 
     Compounds are provided comprising a heteroleptic Ir(III) complex having extended conjugation. Heteroleptic iridium complexes are of great interest because their photophysical, thermal, and electronic properties can be tuned according to the ligands that are attached to the metal center. One advantage to using heteroleptic iridium complexes is that they offer improved device lifetime and a lower sublimation temperature, therefore offering improved manufacturing, as compared to homoleptic Ir(III) complexes. For example, a heteroleptic complex containing 2-phenylpyridine and 2-(biphenyl-3-yl)pyridine, has shown an improved lifetime compared to a related homoleptic complex. Further, the sublimation temperature of the heteroleptic complex is almost 70° C. lower than the homoleptic complex. See, U.S. Pat. No. 8,119,255. Heteroleptic complexes which demonstrate improved stability and low sublimation temperatures, such as those disclosed herein, are highly desirable for use in OLEDs. In particular, the heteroleptic Ir(III) complexes may be especially desirable for use in white organic light emitting devices (WOLEDs). 
     Iridium complexes containing alkyl substituted 2-phenylpyridine ligands have been used as emitters in phosphorescent OLEDs. Alkyl substitution at the 4-position on the phenyl ring of the 2-phenylpyridine ligand normally reduces the device efficiency. For example, devices with tris(2-(5-methyl-phenyl)pyridine)iridium(III) showed much lower external quantum efficiency (EQE) compared to tris(2-phenylpyridine)iridium(III). In the same device structure using 4,4′-di(9H-carbazol-9-yl)-1,1′-biphenyl (CBP) as host with 12% emitter doping concentration, a device with tris(2-(5-methyl-phenyl)pyridine)iridium(III) showed an EQE of 6.6%, whereas the device with tris(2-phenylpyridine)iridium(III) showed an EQE of 9.0%. Therefore, introduction of alkyl substitution at this position is not considered desirable. In the present invention, it was discovered that 4-alkyl substitution on the phenyl ring of the phenylpyridine ligand can improved device EQE in heteroleptic complexes. 
     In some embodiments, a compound having the formula:
 
(L A ) m Ir(L B ) 3-m   (I);
 
is provided. In the compound of formula I, L A  is
 
                         
L B  is selected from the group consisting of:
 
                         
R E  represents mono or di-substitution, or no substitution; R 2 , R A , and R D  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R B , R C , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; X is selected from the group consisting of O, S, and Se; R 1 , R 2 , R A , R B , R C , R D , R E , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfonyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, L B  is selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, L B  is: 
                         
wherein R G  represents mono, di, tri, or tetra-substitution, or no substitution; and wherein R G  is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 
     In some embodiments where L B  is formula (VI), R B  and R E  represent no substitution; and R F  and R G  are each independently selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, halogen, and combinations thereof. In some embodiments where L B  is formula (VI), R G  is fluorine. 
     In some embodiments, L A  is selected from the group consisting of L A1  to L A86  listed below: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, L A  is selected from the group consisting of L A87  to L A172  listed below: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, L A  is selected from the group consisting of L A1 , L A2 , L A3 , L A4 , L A5 , and L A61 . In some embodiments, L A  is L A1 . In some embodiments, L A  is L A2 . In some embodiments, L A  is L A3 . In some embodiments, L A  is L A4 . In some embodiments, L A  is L A5 . In some embodiments, L A  is L A61 . 
     In some embodiments, L B  is selected from the group consisting of L B1  to L B259  listed below: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, L B  is selected from the group consisting of L B57 , L B58 , L B61 , L B67 , and L A69 . In some embodiments, L B  is L B57 . In some embodiments, L B  is L B58 . In some embodiments, L B  is L B61 . In some embodiments, L B  is L B67 . In some embodiments, L B  is L B69 . 
     In some embodiments, L A  is formula II and L B  is formula III. In embodiments where L A  is formula II and L B  is formula III, the compound has the formula I-A: 
                         
In the compound of formula I-A, R 2  and R A  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R C , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; R 1 , R 2 , R A , R C , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, L A  is formula II and L B  is formula IV. In embodiments where L A  is formula II and L B  is formula IV, the compound has the formula I-B: 
                         
In the compound of formula I-B, R 2  and R D  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R B , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; R 1 , R 2 , R B , R D , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, L A  is formula II and L B  is formula V. In embodiments where L A  is formula II and L B  is formula V, the compound has the formula I-C: 
                         
In the compound of formula I-C, R E  represents mono or di-substitution, or no substitution; R 2  represents mono, di, or tri-substitution, or no substitution; R 1 , R B , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , and X 4  are each independently carbon or nitrogen; R 1 , R 2 , R B , R E , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, m is 1. In some embodiments, m is 2. 
     In some embodiments, X is O. In some embodiments, X is S. In some embodiments, X is Se. 
     In some embodiments, no more than 2 of X 1 , X 2 , X 3 , X 4 , and X 5  are nitrogen. In some embodiments, no more than 1 of X 1 , X 2 , X 3 , X 4 , and X 5  is nitrogen. In some embodiments, X 1 , X 2 , X 3 , X 4 , and X 5  are carbon. 
     In some embodiments, R 3  is an alkyl having at least 2 carbons. In some embodiments, 
     R 3  is an alkyl having at least 3 carbons. In some embodiments, R 3  is a cycloalkyl. In some embodiments, R 3  is selected from the group consisting of methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, cyclopentyl, and cyclohexyl, wherein each is optionally partially or fully deuterated. 
     In some embodiments, R 1  is selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, and combinations thereof. 
     In some embodiments, R 2  represents no substitution. 
     In some embodiments, R F  is selected from the group consisting of hydrogen, deuterium, alkyl, cycloalkyl, halogen, and combinations thereof. In some embodiments, R F  is fluorine. 
     In some embodiments, R C , R D , and R E  each represent no substitution. 
     In some embodiments, the compound of formula I is selected from the group consisting of Compound I-1 to Compound I-15 listed below: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the compound of formula I is selected from the group consisting of Compound I-16 to Compound I-19 listed below: 
     
       
         
         
             
             
         
       
     
     In some embodiments, a first device is provided. The first device comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula:
 
(L A ) m Ir(L B ) 3-m   (I).
 
In the compound of formula I, L A  is
 
                         
L B  is selected from the group consisting of:
 
                         
R E  represents mono or di-substitution, or no substitution; R 2 , R A , and R D  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R B , R C , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; X is selected from the group consisting of O, S, and Se; R 1 , R 2 , R A , R B , R C , R D , R E , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, the first device comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula I-A. In embodiments where L A  is formula II and L B  is formula III, the compound has the formula I-A: 
                         
In the compound of formula I-A, R 2  and R A  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R C , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; R 1 , R 2 , R A , R C , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, the first device comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula I-B. In embodiments where L A  is formula II and L B  is formula IV, the compound has the formula I-B: 
                         
In the compound of formula I-B, R 2  and R D  are each independently mono, di, or tri-substitution, or no substitution; R 1 , R B , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; R 1 , R 2 , R B , R D , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, the first device comprises an anode, a cathode, and an organic layer, disposed between the anode and the cathode, comprising a compound having the formula I-C. In embodiments where L A  is formula II and L B  is formula V, the compound has the formula I-C: 
                         
In the compound of formula I-C, R E  represents mono or di-substitution, or no substitution; R 2  represents mono, di, or tri-substitution, or no substitution; R 1 , R B , and R F  are each independently mono, di, tri, or tetra-substitution, or no substitution; X 1 , X 2 , X 3 , X 4 , and X 5  are each independently carbon or nitrogen; R 1 , R 2 , R B , R E , and R F  are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; R 3  is selected from the group consisting of alkyl, cycloalkyl, and combinations thereof; R 3  is optionally partially or fully deuterated; and m is 1 or 2.
 
     In some embodiments, the first device is a consumer product. 
     In some embodiments, the first device is an organic light-emitting device. 
     In some embodiments, the first device comprises a lighting panel. 
     In some embodiments, the organic layer of the first device is an emissive layer and the compound is an emissive dopant. In some embodiments, the organic layer of the first device is an emissive layer and the compound is a non-emissive dopant. 
     In some embodiments, the organic layer of the first device further comprises a host. 
     In some embodiments, the host of the first device comprises a triphenylene containing benzo-fused thiophene or benzo-fused furan; wherein any substituent in the host is an unfused substituent independently selected from the group consisting of C n H 2n+1 , OC n H 2n+1 , OAr 1 , N(C n H 2n+1 ) 2 , N(Ar 1 )(Ar 2 ), CH═CH—C n H 2n+1 , C≡CC n H 2n+1 , Ar 1 , Ar 1 —Ar 2 , C n H 2n —Ar 1 , or no substitution; wherein n is from 1 to 10; and wherein Ar 1  and Ar 2  are independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof. 
     In some embodiments, the host of the first device comprises at least one chemical group selected from the group consisting of carbazole, dibenzothiophene, dibenzofuran, dibenzoselenophene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene. 
     In some embodiments, the host is selected from the group consisting of: 
                                           
combinations thereof.
 
     In some embodiments, the host of the first device comprises a metal complex. 
     In some embodiments, a formulation comprising a compound of formula I is provided. 
     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. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below 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. 
     HIL/HTL: 
     A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but not limit to: a phthalocyanine or porphryin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and sliane derivatives; a metal oxide derivative, such as MoO x ; a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds. 
     Examples of aromatic amine derivatives used in HIL or HTL include, but are not limited to the following general structures: 
     
       
         
         
             
             
         
       
     
     Each of Ar 1  to Ar 9  is selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as 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; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each Ar is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. 
     In some embodiments, Ar 1  to Ar 9  is independently selected from the group consisting of: 
     
       
         
         
             
             
         
       
     
     k is an integer from 1 to 20; X 101  to X 108  is C (including CH) or N; Z 101  is NAr 1 , O, or S; Ar 1  has the same group defined above. 
     Examples of metal complexes used in HIL or HTL include, but are not limited to the following general formula: 
     
       
         
         
             
             
         
       
     
     Met is a metal; (Y 101 -Y 102 ) is a bidentate ligand, Y 101  and Y 102  are independently selected from C, N, O, P, and S; L 101  is an another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal. 
     In some embodiments, (Y 101 -Y 102 ) is a 2-phenylpyridine derivative. 
     In some embodiments, (Y 101 -Y 102 ) is a carbene ligand. 
     In some embodiments, Met is selected from Ir, Pt, Os, and Zn. 
     In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc + /Fc couple less than about 0.6 V. 
     Host: 
     The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant. While the Table below categorizes host materials as preferred for devices that emit various colors, any host material may be used with any dopant so long as the triplet criteria is satisfied. 
     Examples of metal complexes used as host are preferred to have the following general formula: 
     
       
         
         
             
             
         
       
     
     Met is a metal; (Y 103 -Y 104 ) is a bidentate ligand, Y 103  and Y 104  are independently selected from C, N, O, P, and S; L 101  is an another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal. 
     In some embodiments, the metal complexes are: 
     
       
         
         
             
             
         
       
     
     (O—N) is a bidentate ligand, having metal coordinated to atoms O and N. 
     In some embodiments, Met is selected from Ir and Pt. 
     In a further aspect, (Y 103 -Y 104 ) is a carbene ligand. 
     Examples of organic compounds used as host are selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as 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; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atome, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. 
     In some embodiments, the host compound contains at least one of the following groups in the molecule: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     R 101  to R 107  is independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar&#39;s mentioned above. 
     k is an integer from 1 to 20; k′″ is an integer from 0 to 20. 
     X 101  to X 108  is selected from C (including CH) or N. 
     Z 101  and Z 102  is selected from NR 101 , O, or S. 
     HBL: 
     A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED. 
     In some embodiments, compound used in HBL contains the same molecule or the same functional groups used as host described above. 
     In some embodiments, compound used in HBL contains at least one of the following groups in the molecule: 
     
       
         
         
             
             
         
       
     
     k is an integer from 1 to 20; L 101  is an another ligand, k′ is an integer from 1 to 3. 
     ETL: 
     Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons. 
     In some embodiments, compound used in ETL contains at least one of the following groups in the molecule: 
     
       
         
         
             
             
         
       
     
     R 101  is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar&#39;s mentioned above. 
     Ar 1  to Ar 3  has the similar definition as Ar&#39;s mentioned above. 
     k is an integer from 1 to 20. 
     X 101  to X 108  is selected from C (including CH) or N. 
     In some embodiments, the metal complexes used in ETL contains, but are not limited to the following general formula: 
     
       
         
         
             
             
         
       
     
     (O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L 101  is another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal. 
     In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated. Thus, any specifically listed substituent, such as, without limitation, methyl, phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated, and fully deuterated versions thereof. Similarly, classes of substituents such as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc. also encompass undeuterated, partially deuterated, and fully deuterated versions thereof. 
     In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in TABLE 3 below. TABLE 3 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 MATERIAL 
                 EXAMPLES OF MATERIAL 
                 PUBLICATIONS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Hole injection materials 
               
            
           
           
               
               
               
            
               
                 Phthalocyanine and  porphryin compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Starburst triarylamines 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 CF x  Fluorohydrocarbon  polymer 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Appl. Phys. Lett.  78, 673 (2001) 
               
               
                   
               
               
                 Conducting polymers (e.g., PEDOT: PSS,  polyaniline,  polypthiophene) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Synth. Met. 87,  171 (1997) WO2007002683 
               
               
                   
               
               
                 Phosphonic acid and  sliane SAMs 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20030162053 
               
               
                   
               
               
                 Triarylamine or  polythiophene polymers  with conductivity  dopants 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 EP1725079A1 
               
               
                   
               
               
                   
                 and 
                   
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                   
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                   
               
               
                   
               
               
                 Organic compounds  with conductive  inorganic compounds,  such as molybdenum  and tungsten oxides 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20050123751 SID Symposium  Digest, 37, 923  (2006) WO2009018009 
               
               
                   
               
               
                 n-type semiconducting  organic complexes 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 U520020158242 
               
               
                   
               
               
                 Metal organometallic  complexes 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20060240279 
               
               
                   
               
               
                 Cross-linkable  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20080220265 
               
               
                   
               
               
                 Polythiophene based  polymers and  copolymers 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2011075644 EP2350216 
               
               
                   
               
            
           
           
               
            
               
                 Hole transporting materials 
               
            
           
           
               
               
               
            
               
                 Triarylamines (e.g., TPD, α-NPD) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Arylamine carbazole  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Triarylamine with  (di)benzothiophene/  (di)benzofuran 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20070278938,  US20080106190 US20110163302 
               
               
                   
               
               
                 Indolocarbazoles 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Synth. Met. 111,  421 (2000) 
               
               
                   
               
               
                 Isoindole compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Chem. Mater. 15,  3148 (2003) 
               
               
                   
               
               
                 Metal carbene  complexes 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20080018221 
               
               
                   
               
            
           
           
               
            
               
                 Phosphorescent OLED host materials 
               
               
                 Red hosts 
               
            
           
           
               
               
               
            
               
                 Arylcarbazoles 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Appl. Phys. Lett.  78, 1622 (2001) 
               
               
                   
               
               
                 Metal 8- hydroxyquinolates (e.g.,  Alq 3 , BAlq) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 WO2006072002 
               
               
                   
               
               
                 Metal  phenoxybenzothiazole  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Conjugated oligomers  and polymers (e.g., polyfluorene) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Aromatic fused rings 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2009066779,  WO2009066778,  WO2009063833,  US20090045731,  US20090045730,  WO2009008311,  US20090008605,  US20090009065 
               
               
                   
               
               
                 Zinc complexes 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2010056066 
               
               
                   
               
               
                 Chrysene based  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2011086863 
               
               
                   
               
            
           
           
               
            
               
                 Green hosts 
               
            
           
           
               
               
               
            
               
                 Arylcarbazoles 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 WO2001039234 
               
               
                   
               
               
                 Aryltriphenylene  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20060280965 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20060280965 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2009021126 
               
               
                   
               
               
                 Poly-fused heteroaryl  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20090309488 US20090302743 US20100012931 
               
               
                   
               
               
                 Donor acceptor type  molecules 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2008056746 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2010107244 
               
               
                   
               
               
                 Aza- carbazole/DBT/DBF 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 JP2008074939 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20100187984 
               
               
                   
               
               
                 Polymers (e.g., PVK) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Spirofluorene  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2004093207 
               
               
                   
               
               
                 Metal  phenoxybenzooxazole  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2005089025 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2006132173 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 JP200511610 
               
               
                   
               
               
                 Spirofluorene-carbazole  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 JP2007254297 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 JP2007254297 
               
               
                   
               
               
                 Indolocarbazoles 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2007063796 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2007063754 
               
               
                   
               
               
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                 US20050112407 
               
               
                   
               
               
                 Metal phenoxypyridine  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2005030900 
               
               
                   
               
               
                 Metal coordination  complexes (e.g., Zn, Al  with N{circumflex over ( )}N ligands) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20040137268,  US20040137267 
               
               
                   
               
            
           
           
               
            
               
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                 Dibenzothiophene/  Dibenzofuran-carbazole  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2006114966,  US20090167162 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 US20090030202,  US20090017330 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20100084966 
               
               
                   
               
               
                 Silicon aryl compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20050238919 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2009003898 
               
               
                   
               
               
                 Silicon/Germanium aryl  compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 EP2034538A 
               
               
                   
               
               
                 Aryl benzoyl ester 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2006100298 
               
               
                   
               
               
                 Carbazole linked by  non-conjugated groups 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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     EXPERIMENTAL 
     Compound Examples 
     Chemical abbreviations used throughout this document are as follows: DMF is dimethylformamide and DCM is dichloromethane. 
     Example 1 
     Synthesis of Compound I-1 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (The synthesis was disclosed in US2011227049) (2.5 g, 3.37 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (2.15 g, 6.07 mmol), 2-ethoxyethanol (40 mL), and DMF (40 mL) was heated at 130° C. overnight. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-1 (1.8 g, 60.6% yield) which was confirmed by LC-MS. 
     Example 2 
     Synthesis of Compound I-2 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.5 g, 3.25 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (2.071 g, 5.85 mmol), 2-ethoxyethanol (40 mL), and DMF (40 mL) was heated at 130° C. overnight. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-2 (1.88 g, 63.6% yield) which was confirmed by LC-MS. 
     Example 3 
     Synthesis of Compound I-3 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.5 g, 3.25 mmol), 8-(5-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (2.071 g, 5.85 mmol), 2-ethoxyethanol (40 mL), and DMF (40 mL) was heated at 130° C. overnight. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-3 (1.75 g, 59.2% yield) which was confirmed by LC-MS. 
     Example 4 
     Synthesis of Compound I-4 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.0 g, 2.507 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.599 g, 4.51 mmol), 2-ethoxyethanol (25 mL), and DMF (25 mL) was heated at 130° C. overnight. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-4 (1.18 g, 50.2% yield) which was confirmed by LC-MS. 
     Example 5 
     Synthesis of Compound I-5 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (1.55 g, 1.943 mmol), 8-(4-(4-isobutylphenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.525 g, 3.89 mmol), and ethanol (60 mL) was heated at 85° C. for 3 days. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-5 (1.0 g, 52.7% yield) which was confirmed by LC-MS. 
     Example 6 
     Synthesis of Compound I-6 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.2 g, 2.76 mmol), 2-methyl-8-(4-phenylpyridin-2-yl)benzofuro[2,3-b]pyridine (1.669 g, 4.96 mmol), and ethanol (100 mL) was heated at 85° C. for 3 days. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-6 (1.1 g, 43.4% yield) which was confirmed by LC-MS. 
     Example 7 
     Synthesis of Compound I-7 
     
       
         
         
             
             
         
       
     
     A mixture of iridium complex (1.8 g, 2.256 mmol), 8-(4-(4-fluoro-3-isobutylphenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.482 g, 4.51 mmol), 2-ethoxyethanol (40 mL) and DMF (40 mL) was heated at 130° C. overnight. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-7 (1.00 g, 44.6% yield) which was confirmed by LC-MS. 
     Example 8 
     Synthesis of Compound I-8 
     
       
         
         
             
             
         
       
     
     8-(4-(4-fluoro-3,5-diisopropylphenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (2.325 g, 5.30 mmol) and the iridium precursor (2.35 g, 2.95 mmol) were charged into the reaction flask with 40 mL of DMF and 40 mL of 2-ethoxyethanol. This mixture was degassed with nitrogen then was heated in an oil bath set at 130° C. for 18 hours. The solvents were removed under vacuum. The crude residue was passed through a silica gel plug. This crude residue was passed through a silica gel column using DCM/heptanes to elute the column. The clean fractions were combined and concentrated under vacuum yielding Compound I-8 (1.6 g, 53.1% yield) as an orange solid. LC/MS analysis confirmed the mass for the desired product. 
     Example 9 
     Synthesis of Compound I-9 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.5 g, 3.13 mmol), 8-(5-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.99 g, 5.64 mmol), 2-ethoxyethanol (30 mL), and DMF (30 mL) was heated at 130° C. overnight. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM as eluent to obtain Compound I-9 (1.6 g, 57.5% yield) which was confirmed by LC-MS. 
     Example 10 
     Synthesis of Compound I-10 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.5 g, 3.03 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.931 g, 5.45 mmol), and ethanol (100 mL) was heated at 85° C. for 3 days. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-10 (1.3 g, 44.5% yield) which was confirmed by LC-MS. 
     Example 11 
     Synthesis of Compound I-11 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.5 g, 3.03 mmol), 8-(4-(4-isobutylphenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (2.138 g, 5.45 mmol), and ethanol (100 mL) was heated at 85° C. for 3 days. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-11 (2.3 g, 76.0% yield) which was confirmed by LC-MS. 
     Example 12 
     Synthesis of Compound I-12 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (1.9 g, 2.30 mmol), 8-(4-(4-fluoro-3-isobutylphenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.51 g, 3.68 mmol), 2-ethoxyethanol (40 mL), and DMF (40 mL) was heated at 130° C. overnight. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-12 (1.5 g, 63.8% yield) which was confirmed by LC-MS. 
     Example 13 
     Synthesis of Compound I-13 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.5 g, 3.03 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.931 g, 5.45 mmol), and ethanol (120 mL) was heated at 85° C. for 3 days. The solvent mixture was evaporated under vacuum. The residue was run through a short silica plug. The mixture obtained was further purified by silica gel column with DCM/Heptane as eluent to obtain Compound I-13 (0.75 g, 25.7% yield) which was confirmed by LC-MS. 
     Example 14 
     Synthesis of Compound I-14 
     
       
         
         
             
             
         
       
     
     8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.740 g, 4.91 mmol) and the iridium precursor (2.1 g, 2.73 mmol) were charged into the reaction flask with 100 mL of ethanol. This mixture was degassed with nitrogen then was heated at reflux for 3 days. The solvents were removed under vacuum. The crude residue was passed through a silica gel plug. The filtrate was concentrated under vacuum. This crude residue was passed through a silica gel column using DCM/heptanes to elute the column. The clean fractions were combined and concentrated under vacuum yielding Compound I-14 (0.9 g, 36.3% yield) as an orange solid. LC/MS analysis confirmed the mass for the desired product. 
     Example 15 
     Synthesis of Compound I-15 
     
       
         
         
             
             
         
       
     
     8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.876 g, 5.29 mmol) and iridium precursor (2.5 g, 2.94 mmol) were charged into the reaction flask with 100 mL of ethanol. This reaction mixture was degassed with nitrogen then was heated in an oil bath set at 85° C. for 3 days. Heating was discontinued. The reaction mixture was concentrated under vacuum. The crude product was dissolved in DCM and was passed through a silica gel plug. This crude product was then passed through 2×300 g silica gel columns eluting with DCM/Heptanes. Clean product fractions were combined and concentrated under vacuum yielding Compound I-15 (1.52 g, 52.2% yield) as an orange solid. LC/MS analysis confirmed the mass for the desired product. 
     Example 16 
     Synthesis of Compound I-16 
     
       
         
         
             
             
         
       
     
     The iridium precursor (2.0 g, 2.342 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.494 g, 4.22 mmol), DMF 25 mL and 2-ethoxyethanol 25 mL were combined in a 250 mL single neck round bottom flask. A condenser was attached then the system was evacuated and purged with nitrogen three times. The reaction was heated in an oil bath set at 130° C. overnight. The reaction was concentrated down to an orange sludgy solid. The solid was partially dissolved in 200 mL hot DCM and filtered through 200 mg silica gel in fritted Buchner funnel with DCM. The filtrate was concentrated down to 0.84 g of an orange solid. The 0.84 g sample was purified with silica gel using a 75/25 to 25/75 heptane/DCM solvent system to get 0.45 g to an orange-yellow solid for a 19.3% yield. HPLC indicated 99.7% purity and LC/MS indicated it has the correct mass. 
     Example 17 
     Synthesis of Compound I-17 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (2.3 g, 2.69 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.72 g, 4.85 mmol), 2-ethoxyethanol (40 mL) and DMF (40 mL) was heated at 130° C. overnight. The reaction mixture was concentrated to remove solvents and filtered through a small plug of silica gel and further chromatographed to give 0.69 g desired product (26% yield). 
     Example 18 
     Synthesis of Compound I-18 
     
       
         
         
             
             
         
       
     
     A mixture of iridium precursor (1.3 g, 1.37 mmol), 2-methyl-8-(pyridin-2-yl)benzofuro[2,3-b]pyridine-d 6  (0.65 g, 2.46 mmol), 2-ethoxyethanol (20 mL) and DMF (20 mL) was heated at 130° C. overnight. The reaction mixture was concentrated to remove solvents and filtered through a small plug of silica gel and further chromatographed to give 0.76 g desired product (55% yield). (1.52 g, 52.2% yield) as an orange solid. LC/MS analysis confirmed the mass for the desired product. 
     Example 19 
     Synthesis of Compound I-19 
     
       
         
         
             
             
         
       
     
     The iridium precursor (2.5 g, 2.93 mmol), 8-(4-(4-fluorophenyl)pyridin-2-yl)-2-methylbenzofuro[2,3-b]pyridine (1.867 g, 5.27 mmol), DMF 25 mL and 2-ethoxyethanol 25.0 mL were combined in a 250 ml single neck round bottom flask. A condenser was attached then the system was evacuated and purged with nitrogen three times. The reaction was heated in an oil bath set at 130° C. overnight. The reaction was concentrated down to an orange sludgy solid. The solid was dissolved in 100 ml DCM and filtered through 200 g silica gel in fritted Buchner funnel with DCM. The filtrate was concentrated down to 2.3 g of an orange solid. The solid was further purified with silica gel using 25/75 to 15/85 heptane/DCM solvent system to get 0.75 g of an orange-yellow solid (25.8% yield). HPLC indicated 99.5% purity at 254 nm and LC/MS indicated it has the correct mass. 
     Device Examples 
     All example devices were fabricated by high vacuum (&lt;10 −7  Torr) thermal evaporation. The anode electrode is 1200 Å of indium tin oxide (ITO). The cathode consisted of 10 Å of LiF followed by 1,000 Å of Al. All devices are encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (&lt;1 ppm of H 2 O and O 2 ) immediately after fabrication, and a moisture getter was incorporated inside the package. 
     The organic stack of the device examples consisted of sequentially, from the ITO surface, 100 Å of Compound B as the hole injection layer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD) as the hole transporting layer (HTL), 300 Å of the invention compound doped in Compound C as host with as the emissive layer (EML), 50 Å of Compound C as blocking layer 450 Å of Alq 3  (tris-8-hydroxyquinoline aluminum) as the ETL. Comparative Example with Compound A was fabricated similarly to the Device Examples except that the Compound A was used as the emitter in the EML. 
     The device results and data are summarized in Tables 1 and 2 from those devices. As used herein, NPD, Alq, Compound A, Compound B, and Compound C have the following structures: 
     
       
         
         
             
             
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 DEVICE EXAMPLES 
               
            
           
           
               
               
               
               
               
               
            
               
                 DEVICE 
                   
                   
                   
                   
                   
               
               
                 EXAMPLE 
                 HIL 
                 HTL 
                 EML (300 Å, doping %) 
                 BL 
                 ETL 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Comparative 
                 Compound B 
                 NPD 300 Å 
                 Compound C 
                 Compound A 
                 Compound C 
                 Alq 450 Å 
               
               
                 Example 1 
                 100 Å 
                   
                   
                 7% 
                 50 Å 
               
               
                 Inventive 
                 Compound B 
                 NPD 300 Å 
                 Compound C 
                 Compound I-2 
                 Compound C 
                 Alq 450 Å 
               
               
                 Example 1 
                 100 Å 
                   
                   
                 7% 
                 50 Å 
               
               
                 Inventive 
                 Compound B 
                 NPD 300 Å 
                 Compound C 
                 Compound I-4 
                 Compound C 
                 Alq 450 Å 
               
               
                 Example 2 
                 100 Å 
                   
                   
                 7% 
                 50 Å 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 VACUUM THERMAL EVAPORATION 
               
            
           
           
               
               
               
               
               
            
               
                   
                 CIE 
                 λ max 
                 FWHM 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Example 
                 x 
                 y 
                 [nm] 
                 [nm] 
                 EQE 
               
               
                   
                   
               
               
                   
                 Comparative 
                 0.42 
                 0.57 
                 548 
                 71 
                 20.9 
               
               
                   
                 Example 1 
               
               
                   
                 Inventive 
                 0.45 
                 0.55 
                 555 
                 74 
                 24.7 
               
               
                   
                 Example 1 
               
               
                   
                 Inventive 
                 0.45 
                 0.55 
                 554 
                 74 
                 22.3 
               
               
                   
                 Example 2 
               
               
                   
                   
               
            
           
         
       
     
     Table 3 summarizes the performance of the devices. External quantum efficiency (EQE) was measured at 1000 nits. As shown in Table 3 the device prepared using Compound I-2 and Compound I-4 of the present invention showed similar color to the device prepared using comparative Compound A. However, the EQE of the devices with Compound I-2 and Compound I-4 was much higher than the device with comparative Compound A. Therefore, devices prepared with compounds containing an alkyl group at the 4-position of the phenyl ring in the phenylpyridine showed much higher EQEs than a compound that contained a hydrogen at this position. 
     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. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit 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. It is understood that various theories as to why the invention works are not intended to be limiting.