Patent Publication Number: US-9847497-B2

Title: Organic electroluminescent materials and devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional of U.S. Provisional Patent Application Ser. No. 61/941,062, filed Feb. 18, 2014, the entire content of which is incorporated herein by reference. 
     PARTIES TO A 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: The Regents of the University of Michigan, Princeton University, University of Southern California, and 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 compounds for use as emitters and devices, such as organic light emitting diodes, including the same. 
     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 (OLEDs), 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. 
     SUMMARY OF THE INVENTION 
     According to one embodiment, a compound having a structure of Formula M(L A ) x (L B ) y (L C ) z  is provided, where ligand L A  is 
                         
ligand L B  is
 
                         
and ligand L C  is
 
                         
In the structure of Formula M(L A ) x (L B ) y (L C ) z :
 
     M is a metal having an atomic number greater than 40; 
     x is 1, 2, or 3; 
     y is 0, 1, or 2; 
     z is 0, 1, or 2; 
     x+y+z is the oxidation state of the metal M; 
     Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , and Z 6  are each independently selected from C and N; 
     Z D  is selected from N and a carbene carbon; 
     rings C and D are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; 
     R 3  represents mono, or di-substitutions, or no substitutions; 
     R C , and R D  each independently represent mono, di, tri, or tetra-substitution, or no substitution; 
     R 1  and R 2  each independently represent mono, di, or tri-substitution, or no substitutions; 
     R 4  is selected from the group consisting of halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; 
     each of R 1 , R 2 , R 3 , R C , R D , R 11 , R 12 , and R 13  are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and 
     any adjacent substituents of R 1 , R 2 , R 3 , R 4 , R C , R D , R 11 , R 12 , and R 13  are optionally joined to form a ring. 
     According to another embodiment, a device comprising one or more organic light emitting devices is also provided. At least one of the one or more organic light emitting devices can include an anode, a cathode, and an organic layer, disposed between the anode and the cathode, wherein the organic layer can include a compound of Formula M(L A ) x (L B ) y (L C ) z . The device can be a consumer product, an electronic component module, an organic light-emitting device, and/or a lighting panel. 
     According to yet another embodiment, a formulation containing a compound of Formula M(L A ) x (L B ) y (L C ) z  is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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 the structure of ligand L A , ligand L B , and ligand L C  as disclosed herein. 
         FIG. 4  shows a minimized space filling model of a ligand of Compound A and the chemical structure thereof. 
         FIG. 5  shows a minimized space filling model of a ligand of Compound E and the chemical structure thereof. 
     
    
    
     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 one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or 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 OVJD. 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 can be incorporated into a wide variety of electronic component modules (or units) that can be incorporated into a variety of electronic products or intermediate components. Examples of such electronic products or intermediate components include display screens, lighting devices such as discrete light source devices or lighting panels, etc. that can be utilized by the end-user product manufacturers. Such electronic component modules can optionally include the driving electronics and/or power source(s). Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. Such consumer products would include any kind of products that include one or more light source(s) and/or one or more of some type of visual displays. Some examples of such consumer products include flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, laser printers, telephones, cell phones, tablets, phablets, 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 degree 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,” “halogen,” or “halide” 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 alkynyl 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 are used interchangeably and contemplate 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 aromatic and non-aromatic cyclic radicals. Hetero-aromatic cyclic radicals also means heteroaryl. Preferred hetero-non-aromatic cyclic 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 to 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, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. 
     As used herein, “substituted” indicates that a substituent other than H is bonded to the relevant position, such as carbon. Thus, for example, where R 1  is mono-substituted, then one R 1  must be other than H. Similarly, where R 1  is di-substituted, then two of R 1  must be other than H. Similarly, where R 1  is unsubstituted, R 1  is hydrogen for all available positions. 
     The “aza” designation in the fragments described herein, i.e. aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more of the C—H groups in the respective fragment can be replaced by a nitrogen atom, for example, and without any limitation, azatriphenylene encompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein. 
     It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or attached fragment are considered to be equivalent. 
     According to one embodiment, a compound having a structure of Formula M(L A ) x (L B ) y (L C ) z  is disclosed, where ligand L A  is 
                         
ligand L B  is
 
                         
and ligand L C  is
 
                         
In the structure of Formula M(L A ) x (L B ) y (L C ) z :
 
     M is a metal having an atomic number greater than 40; 
     x is 1, 2, or 3; 
     y is 0, 1, or 2; 
     z is 0, 1, or 2; 
     x+y+z is the oxidation state of the metal M; 
     Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , and Z 6  are each independently selected from C and N; 
     Z D  is selected from N and a carbene carbon; 
     rings C and D are each independently a 5 or 6-membered carbocyclic or heterocyclic ring; 
     R 3  represents mono, or di-substitutions, or no substitutions; 
     R C , and R D  each independently represent mono, di, tri, or tetra-substitution, or no substitution; 
     R 1  and R 2  each independently represent mono, di, or tri-substitution, or no substitutions; 
     R 4  is selected from the group consisting of halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; 
     each of R 1 , R 2 , R 3 , R C , R D , R 11 , R 12 , and R 13  are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and 
     any adjacent substituents of R 1 , R 2 , R 3 , R 4 , R C , R D , R 11 , R 12 , and R 13  are optionally joined to form a ring. 
     In some embodiments, at least one of Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , and Z 6  is N, while exactly one of Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , and Z 6  is N in other embodiments. In some embodiments, Z 3 , Z 6 , or both are N. In some embodiments, Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , and Z 6  are each C. 
     In some embodiments, M is a metal selected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Au, and Cu. In some embodiments. M is Ir. 
     In some embodiments, the compound is homoleptic, while the compound is heteroleptic in other embodiments. In some embodiments, the compound has the formula M(L A ) 2 (L C ). In some embodiments, the compound is selected from Compound 1 to Compound 312, where compound x has the formula M(L Ak ) 2 (L Cj ), wherein x=24j+k−24, where k is an integer from 1 to 24, and j is an integer from 1 to 13. 
     In some embodiments, the compound has the formula M(L A )(L B ) 2 . In some embodiments, the compound is selected from Compound 313 to Compound 2112, where compound x has the formula M(L Ak )(L Bj ) 2 , wherein x=(24j+k−24)+312, where k is an integer from 1 to 24, and j is an integer from 1 to 75. 
     In some embodiments, the aryl or heteroaryl of R 4  is substituted by one or more substituent selected from the group consisting of deuterium, 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, cyclobutyl, cyclopentyl, cyclohexyl, and combinations thereof. In some embodiments, R 4  is phenyl substituted at both ortho positions by a substituent selected from the group consisting of deuterium, 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, cyclobutyl, cyclopentyl, cyclohexyl, and combinations thereof. In some embodiments, R 4  is phenyl substituted by an identical substituent at both ortho positions. 
     In some embodiments, ligand L A  has the structure 
                         
where:
 
     R 2′  represents mono, or di-substitutions, or no substitutions; 
     R 2′  and R 5  are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and 
     any adjacent substituents of R 2′ , and R 5  are optionally joined to form a ring. 
     In some embodiments, R 4  and R 5  are identical. 
     In some embodiments, ligand L C  has the formula 
                         
where:
 
     R 6 , R 7 , R 8 , R 9 , and R 10  are independently selected from group consisting of alkyl, cycloalkyl, aryl, and heteroaryl; and 
     at least one of R 6 , R 7 , R 8 , R 9 , and R 10  has at least two C atoms. 
     In some embodiments, ligand L A  is selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, ring C is benzene, and ring D is pyridine. In some embodiments, ligand L B  is selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein X 1 , X 2 , X 3 , X 4 , X 1′ , X 2′ , and X 3′  are each independently selected from the group consisting of N and CR″, 
     wherein each R, R′, and R″ is independently selected from the group consisting of H, alkyl, aryl, heteroaryl, and combinations thereof, and 
     wherein adjacent R, R′, and R″ substituents are optionally joined to form a fused or unfused ring. 
     In some embodiments, ligand L B  is phenyl-pyridine based ligand selected from L B1  through L B41 . In some embodiments, ligand L B  is coordinated to metal M by a carbene carbon and is selected from L B42 -L B66 . Ligand L B  can also be selected from L B67 -L B75 . 
     In some embodiments, ligand L C  is selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the compound is selected from the group consisting of: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the compound can be an emissive dopant. In some embodiments, the compound can produce emissions via phosphorescence, fluorescence, thermally activated delayed fluorescence, i.e., TADF (also referred to as E-type delayed fluorescence), triplet-triplet annihilation, or combinations of these processes. 
     According to another aspect of the present disclosure, a device that includes one or more organic light emitting devices is also provided. At least one of the one or more organic light emitting devices can include an anode, a cathode, and an organic layer disposed between the anode and the cathode. The organic layer may include a host and a phosphorescent dopant. The emissive layer can include a compound according to Formula M(L A ) x (L B ) y (L C ) z , and its variations as described herein. 
     The device can be one or more of a consumer product, an electronic component module, an organic light-emitting device and a lighting panel. The organic layer can be an emissive layer and the compound can be an emissive dopant in some embodiments, while the compound can be a non-emissive dopant in other embodiments. 
     The organic layer can also include a host. In some embodiments, the host can include a metal complex. The host can be a triphenylene containing benzo-fused thiophene or benzo-fused furan. Any substituent in the host can be 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≡C—C n H 2n+1 , Ar 1 , Ar 1 -Ar 2 , and C n H 2n —Ar 1 , or no substitution. In the preceding substituents n can range from 1 to 10; and Ar 1  and Ar 2  can be independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof. 
     The host can be a compound comprising at least one chemical group selected from the group consisting of triphenylene, carbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene, azatriphenylene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene. The host can include a metal complex. The host can be a specific compound selected from the group consisting of: 
                                                                                                 
and combinations thereof.
 
     In yet another aspect of the present disclosure, a formulation that comprises a compound according to Formula M(L A ) x (L B ) y (L C ) z  is described. The formulation can include one or more components selected from the group consisting of a solvent, a host, a hole injection material, hole transport material, and an electron transport layer material, disclosed herein. 
     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 are not limited to: a phthalocyanine or porphyrin 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 silane 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 compound. 
     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 of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; the group consisting of 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 the group consisting of 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, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. 
     In one aspect, Ar 1  to Ar 9  is independently selected from the group consisting of: 
                         
wherein 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: 
                         
wherein Met is a metal, which can have an atomic weight greater than 40; (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 ancillary 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 one aspect, (Y 101 -Y 102 ) is a 2-phenylpyridine derivative. In another aspect, (Y 101 -Y 102 ) is a carbene ligand. In another aspect, 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: 
                         
wherein 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 one aspect, the metal complexes are: 
                         
wherein (O—N) is a bidentate ligand, having metal coordinated to atoms O and N.
 
     In another aspect, 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 of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; the group consisting of 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 the group consisting of 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 group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof. 
     In one aspect, the host compound contains at least one of the following groups in the molecule: 
                                           
wherein R 101  to R 107  is independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, 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 0 to 20 or 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 one aspect, compound used in HBL contains the same molecule or the same functional groups used as host described above. 
     In another aspect, compound used in HBL contains at least one of the following groups in the molecule: 
                         
wherein 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 one aspect, compound used in ETL contains at least one of the following groups in the molecule: 
                         
wherein R 101  is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, 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 another aspect, the metal complexes used in ETL include, but are not limited to the following general formula: 
                         
wherein (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, exciton/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 A below. Table A lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials. 
     
       
         
           
               
               
               
             
               
                 TABLE A 
               
               
                   
               
               
                 MATERIAL 
                 EXAMPLES OF MATERIAL 
                 PUBLICATIONS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Hole injection materials 
               
            
           
           
               
               
               
            
               
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                 Conducting polymers (e.g., PEDOT:PSS, polyaniline, polythiophene) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 Synth. Met. 87, 171 (1997) WO2007002683 
               
               
                   
               
               
                 Phosphonic acid and silane SAMs 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Triarylamine or polythiophene polymers with conductivity dopants 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Organic compounds with conductive inorganic compounds, such as molybdenum and tungsten oxides 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Indolocarbazoles 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Isoindole compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Metal carbene complexes 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 US20080018221 
               
               
                   
               
            
           
           
               
            
               
                 Phosphorescent OLED host materials 
               
               
                 Red hosts 
               
            
           
           
               
               
               
            
               
                 Arylcarbazoles 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 WO2009066779, WO2009066778, WO2009063833, US20090045731, US20090045730, WO2009008311, US20090008605, US20090009065 
               
               
                   
               
               
                 Zinc complexes 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2010056066 
               
               
                   
               
               
                 Chrysene based compounds 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 WO2011086863 
               
               
                   
               
            
           
           
               
            
               
                 Green hosts 
               
            
           
           
               
               
               
            
               
                 Arylcarbazoles 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 Donor acceptor type molecules 
                 
                   
                     
                     
                         
                         
                     
                   
                 
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                 JP200511610 
               
               
                   
               
               
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                 JP2007254297 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 JP2007254297 
               
               
                   
               
               
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                 WO2007063796 
               
               
                   
               
               
                   
                 
                   
                     
                     
                         
                         
                     
                   
                 
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     EXPERIMENTAL 
     Synthetic Examples 
     All reagents were purchased from Aldrich with the exception of Tetrakis(triphenylphosphene) palladium (0), which was purchased from Strem, and 2-bromonicotinic acid, which was purchased from Matrix Scientific. 
     The following is a schematic of the synthesis of meridonal tris(12-methylbenzo[f][1,7]phenanthroline) iridium (III)(Compound D), starting with 2-bromo-N,N-diethylnicotinamide. 
                         
Additional details of each step can be found in the step-by-step explanations below.
 
     Synthesis of 2-bromo-N,N-diethylnicotinamide 
     A 500 mL three neck flask was charged with 27.4 g of 2-bromonicotinic acid and 100 mL of SOCl 2 . The mixture was refluxed for 2 hours and the red-orange solution was cooled to ambient temperature (e.g., 25° C.). Excess SOCl 2  was removed by vacuum distillation, then rinsed 3 times with anhydrous toluene. The resulting solid acid chloride was suspended in 300 mL anhydrous dichloromethane, cooled over an ice bath, and treated with 40 mL diethylamine added in one portion. The solution was then stirred at room temperature overnight (e.g., 16 hours), then washed successively with aqueous sodium bicarbonate and aqueous ammonium chloride. The organic phase was then dried over sodium sulfate and evaporated in vacuo to yield 2-bromo-N,N-diethylnicotinamide as a light brown oil (29.2 g. 84%). 
     Synthesis of 2-(2,6-dimethylphenyl)-N,N-diethylnicotinamide 
     A 250 mL round bottom flask fitted with a reflux condenser was charged with 8.5 g of 2-bromo-N,N-diethylnicotinamide, 5.3 g (1.1 eq) of 2,6-dimethylphenylboronic acid, 100 mL of 1,4 dioxane, and 50 mL of 2M aqueous potassium carbonate. The biphasic mixture was sparged with nitrogen with vigorous magnetic stirring. After 10 minutes, 1.4 g of tetrakis(triphenylphosphene) palladium (0) was added and the mixture was sparged with nitrogen for a further 10 minutes. The reaction was held at 90° C. for 20 hours, cooled, then diluted with 200 mL of ethyl acetate. The organic phase is washed with water (100 mL), then brine (100 mL), before being dried over sodium sulfate. The organic phase was concentrated to a viscous amber oil, which was chromatographed over silica with an ethyl acetate:hexanes (1:1) mixture to give a yellow solid. Recrystallization in diethyl ether layered with hexanes yielded colorless prisms of 2-(2,6-dimethylphenyl)-N,N-diethylnicotinamide (3.6 g, 38% yield). 
     Synthesis of 10-methylbenzo[h]quinolin-5-ol 
     A flame dried 250 mL schlenk flask was charged with 2.2 g of 2-(2,6-dimethylphenyl)-N,N-diethylnicotinamide and 100 mL of anhydrous tetrahydrofuran (THF). The solution was cooled to −78° C. under a nitrogen atmosphere with magnetic stirring. A 2 M solution of lithium diisopropylamide (LDA) (5 mL, 10 mMol) was added dropwise and the reaction was allowed to warm to room temperature overnight. Saturated aqueous ammonium chloride (50 mL) was added and the volume was reduced under reduced pressure. Dichloromethane (100 mL) was added and the organic phase was washed with water (100 mL), then brine (100 mL), before being dried over sodium sulfate. The organic phase was concentrated to a dark brown oil which was chromatographed over silica with a ethyl acetate:hexanes (1:3) solution to give 10-methylbenzo[h]quinolin-5-ol as a colorless solid (1.29 g, 79%). 
     Synthesis of 10-methylbenzo[h]quinoline-5,6-dione 
     A 1 L beaker was charged with 1.29 g of 10-methylbenzo[h]quinolin-5-ol, 100 mL of dichloromethane, 200 mL of acetone, and 300 mL of saturated aqueous sodium bicarbonate. The colorless biphasic mixture was stirred vigorously and 10 g of oxone monopersulfate (KHSO 5 .0.5 KHSO 4 .0.5K2SO 4 ) was added in 10 portions with care to avoid excessive foaming. After 1 hour the bright yellow organic phase was separated, washed with brine (100 mL), and concentrated in vacuo to give a yellow solid. Recrystallization from hot ethanol yielded orange needle-like prisms of 10-methylbenzo[h]quinoline-5,6-dione (835 mg, 61%). 
     Synthesis of 9-methylbenzo[h][1,2,4]triazino[5,6-f]quinoline 
     A 250 mL schlenk flask was charged with 756 mg of 10-methylbenzo[h]quinoline-5,6-dione and 200 mL of anhydrous methanol. A formamidrazone solution freshly prepared by adding 240 uL anhydrous hydrazine to 800 mg formamidine acetate in 15 mL dry methanol was then added to the solution. The suspension was stirred magnetically at room temperature under nitrogen atmosphere for 16 hours, after which the pale orange precipitate was collected by filtration and washed with 20 mL of ethanol. The solid powder was allowed to air dry yielding 9-methylbenzo[h][1,2,4]triazino[5,6-f]quinoline and 8-methylbenzo[h][1,2,4]triazino[5,6-f]quinoline as a 3:2 mixture which was used without separation (516 mg, 62%). 
     Synthesis of 12-methylbenzo[f][1,7]phenanthroline, (BzpH) 
     A 100 mL schlenk flask fitted with a reflux condenser was charged with 2 mL of norbonadiene, 25 mL of triethylene glycol, and 516 mg of a 3:2 mixture of 9-methylbenzo[h][1,2,4]triazino[5,6-f]quinoline and 8-methylbenzo[h][1,2,4]triazino[5,6-f]quinoline. The reaction mixture was sparged with nitrogen for 10 minutes and then heated to 170° C. for 16 hours. The reaction was cooled to room temperature, diluted with dichloromethane (100 mL) and washed with water (5×50 mL). The organic phase was dried over sodium sulfate and then dried in vacuo. The pale yellow residue was chromatographed twice over silica with 15% ethylacetate in hexanes, first eluting 9-methylbenzo[f][4,7]phenanthroline (iso-BzpH), and then 12-methylbenzo[f][1,7]phenanthroline (BzpH), which crystallized as colorless plates by slow evaporation of tetrahydrofuran (THF) (150 mg, 49%). 
     Synthesis of Meridonal tris(12-methylbenzo[f][1,7]phenanthroline) iridium (III), (Mer-Ir(Bzp) 3 )(Compound D) 
     A 15 mL Schlenk tube fitted with a reflux condenser was charged with 80 mg of BzpH, 20 mg of tris(acetylacetonato)iridium (III), and 4 mL of glycerol. The reaction mixture was deoxygenated by 3 cycles of vacuum (15 minutes) and nitrogen refill. The reaction mixture was placed in a sand bath and heated under nitrogen to vigorous reflux (ca. 350° C.) for 16 hours. The dark brown solution was allowed to cool to ambient temperature, diluted with 100 mL of water, then 25 mL of brine, and extracted with dichloromethane (100 mL). The organic phase was dried in vacuo and chromatographed over silica with an ethyl acetate:hexanes (1:1) solution to yield mer-Ir(Bzp) 3  as a yellow solid (10 mg, 27%). 
     Synthetic Route for Compound A 
     An analogous synthetic route for producing Compound A is provided below. 
     
       
         
         
             
             
         
       
     
     Proposed Synthetic Route for Compound 9 
     
       
         
         
             
             
         
       
     
     Proposed Synthesis of tetrakis(12-phenylbenzo[f][1,7]phenanthroline)-u-dichloro diiridium (III) 
     A schlenk flask fitted with a reflux condenser can be charged with 2 equivalents of 12-phenylbenzo[f][1,7]phenanthroline, 1 equivalent of iridium trichloride hexahydrate, ethoxyethanol, and water. The mixture can be sparged with nitrogen and then heated to reflux under nitrogen atmosphere (ca. 140 C). After 16 hours the reaction would be cooled to room temperature and diluted with water. The precipitate would then be collected by filtration and washed with methanol. 
     Proposed Synthesis of bis(12-phenylbenzo[f][1,7]phenanthroline) acetoacetonato iridium (III), (compound 9) 
     A round bottom flask can be charged with 1 equivalent of tetrakis(12-phenylbenzo[f][1,7]phenanthroline)-u-dichloro diiridium (III), 3 equivalents of 2,4-pentanedione, 3 equivalents of potassium carbonate, and 1,2-dichloroethane. The reaction would then be sparged with nitrogen and heated to reflux (ca. 90 C) for 3 hours. The reaction could then be cooled, the solvent evaporated to dryness, and the residue chromatographed on silica to isolate bis(12-phenylbenzo[f][1,7]phenanthroline) acetoacetonato iridium (III) (Compound 9). 
     Analysis of Compounds 
     As can be seen in the space filling model, calculated by density functional theory (DFT), and shown in  FIG. 4 , the aryl substituent sterically shields the uncoordinated nitrogen from close contact of a neighboring intra or intermolecular proton atom. As shown in  FIG. 5 , the space filling model of Compound E shows close contact of an intramolecular proton from the neighboring methyl substituent. In contrast, the unsubstituted Comparative Example 1 has an unprotected nitrogen that will be more susceptible to being protonated by any neighboring molecule in the solid state. 
     Furthermore, as the aryl substitution necessarily twists out of the plane of the ligand, there is a minimal effect on the triplet energy of the complex. DFT calculations are shown in Table 1 below. DFT calculations were performed using the B3LYP/cep-31 g/THF functional, basis set, and solvent polarization, respectively. It can be seen that Compound A has a calculated triplet of 488 nm compared to 490 nm for Compound E, and 482 nm for Comparative Example 1. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 HOMO 
                 LUMO 
                 Gap 
                 Dipole 
                 S1 THF   
                 T1 THF   
               
               
                   
                 Structure 
                 (eV) 
                 (ev) 
                 (ev) 
                 (Debye) 
                 (nm) 
                 (nm) 
               
               
                   
               
             
            
               
                 Comparative Example 1 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 −5.83 
                 −1.99 
                 −3.85 
                 15.00 
                 420 
                 482 
               
               
                   
               
               
                 Compound A 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 −5.79 
                 −1.99 
                 −3.80 
                 15.40 
                 427 
                 488 
               
               
                   
               
               
                 Compound B 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 −5.76 
                 −1.96 
                 −3.81 
                 15.60 
                 428 
                 503 
               
               
                   
               
               
                 Compound C 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 −5.75 
                 −1.94 
                 −3.82 
                 15.66 
                 424 
                 491 
               
               
                   
               
               
                 Compound D 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 −5.75 
                 −1.96 
                 −3.79 
                 13.43 
                 430 
                 487 
               
               
                   
               
               
                 Compound E 
                 
                   
                     
                     
                         
                         
                     
                   
                 
                 −5.70 
                 −1.89 
                 −3.80 
                 14.20 
                 427 
                 490 
               
               
                   
               
            
           
         
       
     
     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.