Emissive Material for Organic Emitting Diodes

BACKGROUND

Cross Reference to Related Applications

[0001] This application claims the benefit of U.S. provisional patent application 62/013,426 filed June 17, 2014, the entire disclosure of which is incorporated by reference herein.

Field

[0002] The present disclosure generally relates to a field of organic chemistry and organic light-emitting diode (OLED) materials, such as emissive material that can be used in OLED applications.

Description of the Related Art

[0003] Organic light-emitting devices have been widely developed for flat panel displays, and are moving fast toward solid state lighting (SSL) applications. Organic light emitting diodes (OLEDs) comprise a cathode, an emissive layer, and an anode. Light emitted from an OLED device is the result of recombination of positive charges (holes) and negative charges (electrons) inside an organic (emissive) layer. The holes and electrons combine within a single molecule or a small cluster of molecules to generate excitons, which are molecules in an excited state, or groups of organic molecules bound together in an excited state. When the organic molecules release the required energy and return to their stable state, photons are generated. An organic compound or group of compounds which emits photons are referred as an electro-fluorescent material or electro-phosphorescent material depending on the nature of the radiative process. Thus, OLED emissive compounds may be selected for their ability to absorb primary radiation and emit radiation of a desired wavelength. Despite the advantages, emissive materials in OLED devices contain expensive noble metals, such as iridium, which results high overall material cost. Thus, there is a need for OLED materials that have high efficiency while avoiding the use of expensive noble metals. SUMMARY

[0004] In accordance with the embodiments broadly described herein, provided are compounds for an OLED that are based on thermally activated delayed fluorescence (TADF) materials that do not use expensive noble metal emissive compounds to achieve electroluminescence.

[0005] Some embodiments include a compound represented by Formula

1 :

(Formula 1 )

wherein R ¹ is substituted carbazolyl or optionally substituted benzocarbazolyl; and R ² , R ³ , and R ⁴ are independently optionally substituted carbazolyl or optionally substituted benzocarbazolyl.

[0006] Some embodiments include optionally substituted 9,9',9",9"'-(3,6- bis(trifluoromethyl)benzene-1 ,2,4,5-tetrayl)tetrakis(3,6-diphenyl-9/-/-carbazole) (Emitting Compound 1 [EC-1 ]).

[0007] Some embodiments include light-emitting elements comprising a compound described herein.

[0008] Some embodiments include a light-emitting device comprising a light-emitting element comprising a compound described herein.

[0009] Some embodiments include an organic light-emitting diode device comprising: a cathode; an anode; and a light-emitting layer disposed between, and electrically connected to, the anode and the cathode, wherein the light-emitting layer comprises a compound described herein.

[0010] Some embodiments provide an organic light-emitting diode device comprising: a cathode; an anode; and a light-emitting layer disposed between and electrically connected to the anode and the cathode; wherein the light-emitting layer comprises a host compound described herein.

[001 1] Some embodiments provide an organic light-emitting diode device comprising a cathode; an anode; a light-emitting layer disposed between and electrically connected to the anode and the cathode; a hole-transport layer between the anode and the light-emitting layer; and an electron-transport layer between the cathode and the light-emitting layer; wherein at least one of the light-emitting layer, the hole-transport layer, and the electron-transport layer comprise a host compound described herein.

[0012] These and additional embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic of a device incorporating an embodiment of a compound described herein.

DETAILED DESCRIPTION

[0014] By employing a newly designed molecular structure, a series of emissive materials are described that can be used in OLED device applications.

[0015] As used herein, the term "optionally substituted" is used to denote a group, such as carbazolyl, benzocarbazolyl, phenoxazolyl, phenothiazolyl, phenazolyl, phenyl, alkyl, etc., that may be substituted or unsubstituted. A substituted group is derived from the unsubstituted parent structure wherein one or more substituents occupy one or more positions that are occupied by hydrogen atoms on the parent structure. Any suitable substituent may be present, such as a substituent having a molecular weight of 15 Da to 500 Da, 400 Da, 300 Da, 200 Da, 100 Da, or 50 Da; and/or a substituent represented by a formula: C0-15H0-35O0-2S0- 2N0-2P0-1CI0-1 F0-5, Co-i5Ho-350o-2 o-2Clo-i Fo-5,Co-6Ho-i50o-2No-2Clo-i Fo-3, or C0-3H0-10O0- 2No-2Clo-iFo-5- In some embodiments, any substituents can independently be independently optionally substituted alkyl, -O-alkyl (e.g. -OCH ₃ , -OC ₂ H5, -OC ₃ H ₇ , - OC ₄ H ₉ , etc.), -S-alkyl (e.g. -SCH ₃ , -SC ₂ H ₅ , -SC ₃ H ₇ , -SC ₄ H ₉ , etc.), -NR'R", -OH, -SH, -CN, -CF ₃ , -NO2, perfluoroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amine, or a halogen, wherein R' and R" are independently H or optionally substituted alkyl. Wherever a substituent is described as "optionally substituted," that substituent can be substituted with the above substituents.

[0016] For convenience, the term "molecular weight" is used with respect to a moiety or part of a molecule to indicate the sum of the atomic masses of the atoms in the moiety or part of a molecule, even though it may not be a complete molecule.

the term "carbazolyl" refers to the ring

includes, but is not limited

, wherein R'" can be H, C C ₃ alkyl, C C ₃ perfluoroalkyl, optionally substituted aryl, e.g., an optionally substituted phenyl, optionally substitituted carbazolyl, optionally substituted amine, optionally substituted phenoxazolyl, optionally substituted phenothiazolyl, and optionally substituted phenazolyl.

[0018] As used herein, the term "benzocarbazolyl" refers to a ring system

such as, but not limited to, , , and

[0019] As used herein, the term "phenoxazolyl" refers to a ring system

such as, but not limited to,

[0020] As used herein, the term "phenothiazolyl" refers to a ring system

such as, but not limited to, .

[0021] As used herein, the term "phenazolyl" refers to a ring system such

as, but not limited to,

[0022] As used herein, the term "phenyl" refers to the aryl ring system, which includes, but is not limited to, (denoted as ^Ph_ i ). [0023] As used herein, the term "diphenylamine" refers to a ring system

such as, but not limited to, .

[0024] As used herein, the term "phenylnaphthylamine" refers to

system such as, but not limited to,

[0025] As used herein, the term "perfluoroalkyl" refers to fluoroalkyl with a formula C _n F _2n +i for a linear or branched structure, e.g., CF ₃ , C ₂ F ₅ , C ₃ F ₇ , C F ₉ , C ₅ Fn , C ₆ F ₃ , etc., or C _n F _2n -i for a cyclic structure, e.g., cyclic C ₃ F ₅ , cyclic C F ₇ , cyclic C ₅ F ₉ , cyclic C-6F-I 1 , etc. In other words, every hydrogen atom in alkyl is replaced by fluorine. For example, while not intending to be limiting, Ci _-3 perfluoroalkyl refers to CF ₃ , C ₂ F ₅ , and C ₃ F ₇ isomers.

[0026] As used herein, the term "aryl" refers to an aromatic ring or ring system. Exemplary non-limiting aryl groups are phenyl, naphthyl, etc. The term "C _x-y aryl" refers to an aryl where the ring or ring system has x-y carbon atoms. The indicated number of carbon atoms for the ring or ring system does not include or limit the number of carbon atoms in any substituents attached to the ring or ring system. Examples include, but are not limited to, optionally substituted phenyl, optionally substituted naphthyl, optionally substituted anthracenyl, optionally substituted p- interphenylene, optionally substituted 1 ,4-internaphthylene, and optionally substituted 9, 1 0-interanthracenylene. These are shown below in their unsubstituted forms. However, any carbon not attached to the remainder of the molecule may optionally have a substituent. In some embodiments, the aryl can be, but is not limited to:

NC , and NC [0027] As used herein, the term "heteroaryl" refers to any aryl which has one or more heteroatoms in the ring or ring system. The term "C _X-Y heteroaryl" refers to a heteroaryl where the ring or ring system has x-y carbon atoms. The indicated number of carbon atoms for the ring or ring system does not include or limit the number of carbon atoms in any substituents attached to the ring or ring system. Examples of "heteroaryl" may include, but are not limited to, carbazolyl, benzocarbazolyl, pyridinyl, pyrimidinyl, furyl, thienyl, oxazolyl, thiazolyl, imidazolyl, indolyl, quinolinyl, benzofuranyl, benzothienyl, benzooxazolyl, benzothiazolyl, benzoimidazolyl, phenoxazolyl, phenothiazolyl, phenazolyl, etc. In some embodiments, the "heteroaryl" can be an optionally substituted pyridinyl. In some embodiments, the "heteroaryl" can be an optionally substituted pyrimidinyl. In some embodiments, the "heteroaryl" can be an optionally substituted carbazolyl. In some embodiments the "heteroaryl" can be an optionally substituted benzocarbazolyl. In some embodiments the "heteroaryl" can be an optionally substituted phenoxazolyl. In some embodiments the "heteroaryl" can be an optionally substituted phenothiazolyl. In some embodiments the "heteroaryl" can be an optionally substituted phenazolyl.

[0028] As used herein, the term "alkyl" refers to a hydrocarbon moiety containing no double or triple bonds. Examples include, but are not limited to, linear alkyl, branched alkyl, cycloalkyl, and combinations thereof. Alkyl may also be defined by the following general formulas: the general formula for linear or branched monovalent alkyl (e.g. -alkyl attaching in a single position) not containing a cyclic structure is C _N H _2n +i , and the general formula for monovalent alkyl containing one ring is C _N H _2n -i - A CX-Y alkyl or CX-CY alkyl is an alkyl having from X to Y carbon atoms. For example, C-1-12 alkyl or C1-C12 alkyl includes linear, branched, or cyclic alkyl containing 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , or 12 carbon atoms.

[0029] Some embodiments include an emissive compound for use in emissive elements of organic light-emitting devices, wherein the compound is represented by Formula 1 .

[0030] With respect to Formula 1 , R ¹ can be any electron donating substituent, such as optionally substituted carbazolyl, substituted carbazolyl, or optionally substituted benzocarbazolyl. In some embodiments, R ¹ is R ¹ -X, wherein R ¹ is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is C1-6 alkyl (such as CH ₃ ; C ₂ H ₅ ; linear, branched, or cyclic C ₃ alkyl; linear, branched, or cyclic C ₄ alkyi; linear, branched, or cyclic C5 alkyi; linear, branched, or cyclic C ₆ alkyi); optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl. In some embodiments, X is unsubstituted phenyl.

[0031] In some embodiments, each substituent of R ¹ , if present, has a molecular weight of 15 Da to 500 Da, 400 Da, 300 Da, or 200 Da, and is represented by a formula: Co-i5Ho-350o-2No-2Clo-iFo-5-

[0032] With respect to Formula 1 , R ² can be any electron donating substituent, such as optionally substituted carbazolyl or optionally substituted benzocarbazolyl. In some embodiments, R ² is R ² -X, wherein R ² is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is C-i-6 alkyi (such as CH ₃ ; C ₂ H ₅ ; linear, branched, or cyclic C ₃ alkyi; linear, branched, or cyclic C alkyi; linear, branched, or cyclic C ₅ alkyi; linear, branched, or cyclic C ₆ alkyi); optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl. In some embodiments, X is unsubstituted phenyl.

[0033] In some embodiments, each substituent of R ² , if present, has a molecular weight of about 15 Da to about 500 Da, about 400 Da, about 300 Da, or about 200 Da, and is represented by a formula: C0-15H0-35O0-2N0-2CI0-1 F0-5.

[0034] With respect to Formula 1 , R ³ can be any electron donating substituent, such as optionally substituted carbazolyl or optionally substituted benzocarbazolyl. In some embodiments, R ³ is R ³ -X, wherein R ³ is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is C-i-6 alkyi (such as CH ₃ ; C2H5; linear, branched, or cyclic C3 alkyi; linear, branched, or cyclic C ₄ alkyi; linear, branched, or cyclic C ₅ alkyi; linear, branched, or cyclic C ₆ alkyi); optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl. In some embodiments, X is unsubstituted phenyl.

[0035] In some embodiments, each substituent of R ³ , if present, has a molecular weight of about 15 Da to about 500 Da, about 400 Da, about 300 Da, or about 200 Da, and is represented by a formula: C0-15H0-35O0-2N0-2CI0-1 F0-5.

[0036] With respect to Formula 1 , R ⁴ can be any electron donating substituent, such as optionally substituted carbazolyl or optionally substituted benzocarbazolyl. In some embodiments, R ⁴ is R ⁴ -X, wherein R ⁴ is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is d-6 alkyl (such as CH ₃ ; C ₂ H ₅ ; linear, branched, or cyclic C ₃ alkyl; linear, branched, or cyclic C alkyl; linear, branched, or cyclic C ₅ alkyl; linear, branched, or cyclic C ₆ alkyl); optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl. In some embodiments, X is unsubstituted phenyl.

[0037] In some embodiments, each substituent of R ⁴ , if present, has a molecular weight of 15 Da to 500 Da, 400 Da, 300 Da, or 200 Da, and is represented by a formula: Co-i5Ho-350o-2No-2Clo-iFo-5- 1, R ² , R ³ , and R ⁴ can independently be:

[0039] In some embodiments, an emissive compound can be:

9,9',9",9"'- (3,6-bis(trifluoromethyl)benzene-1 ,2,4,5-tetrayl)tetrakis(3,6- diphenyl-9/-/-carbazole) (EC-1 ).

[0040] In some embodiments, a light-emitting element is provided comprising at least one of the aforementioned compounds, e.g., EC-1 . In some embodiments, an emissive layer can comprise any of the aforementioned compounds. In some embodiments, a light-emitting device is provided comprising any of the aforementioned light-emitting elements.

[0041] The compounds described herein, e.g. a compound of Formula 1 , or an optionally substituted 9,9',9",9"'-(3,6-bis(trifluoromethyl)benzene-1 ,2,4,5- tetrayl)tetrakis(3,6-diphenyl-9/-/-carbazole) (referred to herein as "a subject compound), may be used as light-emitting dopants in light-emitting layers of OLED devices. For example, a light-emitting layer may comprise, or consist of, a subject compound dispersed in a host compound. Alternatively, a light-emitting layer may be a neat layer of a subject compound. In some embodiments, a light-emitting layer may have less than about 1 %, about 0.5%, about 0.1 %, about 0.01 % by weight, or may be substantially free of, emissive metal complexes, metal complexes, or noble metals.

[0042] Some embodiments provide an organic light-emitting diode device 10 comprising a cathode 20, an anode 30, and a light-emitting layer 40 disposed between and electrically connected to the anode and the cathode. Some embodiments additionally comprise a hole-transport layer 50 between the anode and the light-emitting layer 40 and an electron-transport layer 60 between the cathode 20 and the light-emitting layer 40, wherein the light-emitting layer can comprise an emitting compound described herein. In some embodiments, the hole-transport layer 50 can comprise a first hole-transport layer 50A, and a second first hole- transport layer 50B. The second hole-transport layer 50B can also function as an electron-blocking layer. In some embodiments, second hole-transport layer 50B can comprise a high T1 material. In some embodiments, a hole-injection layer 70 can be disposed between the anode 30 and the hole-transport layer 50. In some embodiments, an electron-injection layer 80 can be between the cathode 20 and the electron-transport layer 60. Figure 1 provides an illustration of an embodiment of an organic light-emitting device incorporating the compounds disclosed herein.

[0043] An anode layer may comprise a conventional material such as material having a higher work function than the cathode layer, e.g. a metal, mixed metal, alloy, metal oxide or mixed-metal oxide, or a conductive polymer. Examples of suitable metals include the Group 1 metals, the metals in Groups 4, 5, 6, and the Group 8-10 transition metals. If the anode layer is to be light-transmitting, mixed- metal oxides of Group 12, 13, and 14 metals or alloys thereof, such as Au, Pt, and indium-tin-oxide (ITO), may be used. The anode layer may include an organic material such as polyaniline, e.g., as described in "Flexible light-emitting diodes made from soluble conducting polymer," Nature, vol. 357, pp. 477-479 (1 1 June 1992). Examples of suitable high work function metals include but are not limited to Au, Pt, indium-tin-oxide (ITO), or alloys thereof. In some embodiments, the anode layer can have a thickness in the range of about 1 nm to about 1000 nm.

[0044] A cathode layer may include a material having a lower work function than the anode layer. Examples of suitable materials for the cathode layer include those selected from alkali metals of Group 1 , Group 2 metals, Group 12 metals including rare earth elements, lanthanides and actinides, materials such as aluminum, indium, calcium, barium, samarium and magnesium, and combinations thereof. Lithium-containing organometallic compounds, LiF, and Li ₂ 0 may also be deposited between the organic layer and the cathode layer to lower the operating voltage. Suitable low work function metals include but are not limited to Al, Ag, Mg, Ca, Cu, Mg/Ag, LiF/AI, CsF, CsF/AI or alloys thereof. In some embodiments, the cathode layer can have a thickness in the range of about 1 nm to about 1000 nm.

[0045] The light-emissive layer may comprise a subject compound, and may further comprise a host. The emissive component, e.g. a subject compound, may be a fluorescent and/or a phosphorescent compound. Similarly, a host may be a fluorescent and/or a phosphorescent compound, often with a T1 or S1 that is higher than that of the emissive component. An emissive layer may comprise a neat subject compound, or a subject compound and/or another dopant and a host. In some embodiments, the dopant, e.g. a subject compound, is up to about 10% (w/w) of the host, or from about 0.1 % (w/w) to about 5% (w/w) of the host.

[0046] Any suitable host may be used in a light-emitting layer. Some examples of useful host materials are described in co-pending patent applications, e.g., United States Patent Application Publication No. US2012/0193614 (published August 2, 2012, application number 13/360,639, filed January 27, 2012); United States Patent Application Publication No. US2012/0179089 (published July 12, 2012, application number 13/232,837, filed September 14, 201 1 ); United States Patent Application Publication No. US201 1/0251401 (published October 13, 201 1 , application number 13/166.246, filed June 22, 201 1 ); United States Patent Nos., 8,426,040, issued April 23, 2013, 8,263,238, issued September 1 1 , 2012, and 8,062,772, issued November 22, 201 1 , all of which are incorporated by reference in their entireties for their description of host materials. Other exemplary host materials included in the light-emitting layer can be, but are not limited to, an optionally substituted compound selected from: an aromatic-substituted amine, an aromatic- substituted phosphine, a thiophene, an oxadiazole, 2-(4-biphenylyl)-5-(4-tert- butylphenyl)-1 ,3,4-oxadiazole (PBD), 1 ,3-bis(N,N-t-butyl-phenyl)-1 ,3,,4-oxadiazole (OXD-7), a triazole, 3-phenyl-4-(1 '-naphthyl)-5-phenyl-1 ,2,4-triazole (TAZ), 3,4,5- triphenyl-1 ,2,3-triazole, 3,5-bis(4-tert-butyl-phenyl)-4-phenyl[1 ,2,4]triazole, an aromatic phenanthroline, 2,9-dimethyl-4,7-diphenyl-phenanthroline (bathocuproine or BCP), 2,9-dimethyl-4,7-diphenyl-1 ,10-phenanthroline, a benzoxazole, a benzothiazole, a quinoline, aluminum tris(8-hydroxyquinolate) (Alq3), a pyridine, a dicyanoimidazole, cyano-substituted aromatic, 1 ,3,5-tris(2-N- phenylbenzimidazolyl)benzene (TPBI), 4,4'-bis[N-(naphthyl)-N-phenyl- aminojbiphenyl (a-NPD), N,N'-bis(3-methylphenyl)N,N'-diphenyl-[1 , 1 '-biphenyl]-4,4'- diamine (TPD), 4,4'-bis[N,N'-(3-tolyl)amino]-3,3'-dimethylbiphenyl (M14), 4,4'- bis[N,N'-(3-tolyl)amino]-3,3'-dimethylbiphenyl (HMTPD), 1 ,1 -bis(4-bis(4- methylphenyl) aminophenyl) cyclohexane, a carbazole, 4,4'-N,N'-dicarbazole- biphenyl (CBP), poly(9-vinylcarbazole) (PVK), N,N'N"-1 ,3,5-tricarbazoloylbenzene (tCP), a polythiophene, a benzidine, N,N'-bis(4-butylphenyl)-N,N'- bis(phenyl)benzidine, a triphenylamine, 4,4',4"-tris(N-(naphthylen-2-yl)-N- phenylamino)triphenylamine, 4,4 4''-tris(3-methylphenylphenylamino)tnphenylamine (MTDATA), dibenzo[b,d]thiophene-2,8-diylbis(diphenylphosphine oxide) (PPT), 3,3'- di(9H-carbazol-9-yl)-1 ,1 '-biphenyl (mCBP), a phenylenediamine, a polyacetylene, and a phthalocyanine metal complex.

[0047] The thickness of the light-emitting layer may vary. In some embodiments, the light-emitting layer has a thickness in the range of about 20 nm to about 200 nm. In some embodiments, the light-emitting layer has a thickness in the range of about 20 nm to about 150 nm.

[0048] In some embodiments, the light-emitting device may further comprise a hole-transport layer between the anode and the light-emitting layer and an electron-transport layer between the cathode and the light-emitting layer. In some embodiments, all of the light-emitting layer, the hole-transport layer and the electron-transport layer comprise a host compound described herein.

[0049] In some embodiments, the hole-transport layer may comprise at least one hole-transfer material. Suitable hole-transport materials include, but are not limited to, 1 ,1 -bis(4-bis(4-methylphenyl) aminophenyl) cyclohexane; 2,9- dimethyl-4,7-diphenyl-1 ,10-phenanthroline; 3,5-bis(4-tert-butyl-phenyl)-4- phenyl[1 ,2,4]triazole; 3,4,5-triphenyl-1 ,2,3-triazole; 4,4',4"-tris(N-(naphthylen-2-yl)-N- phenylamino)triphenylamine; 4,4',4'-tris(3-methylphenylphenylamino)triphenylamine (MTDATA); 4,4'-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (a-NPD); 4,4'-bis[N,N'-(3- tolyl)amino]-3,3'-dimethylbiphenyl (HMTPD); 4,4'-bis[N,N'-(3-tolyl)amino]-3,3'- dimethylbiphenyl (M14); 4,4'-N,N'-dicarbazole-biphenyl (CBP); 1 ,3-N,N-dicarbazole- benzene (mCP); poly(9-vinylcarbazole) (PVK); a benzidine; a carbazole; a phenylenediamine; a phthalocyanine metal complex; a polyacetylene; a polythiophene; a triphenylamine; an oxadiazole; copper phthalocyanine; N,N'-bis(3- methylphenyl)N,N'-diphenyl-[1 ,1 '-biphenyl]-4,4'-diamine (TPD); N,N'N"-1 ,3,5- tricarbazoloylbenzene (tCP); N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine; 4,4'- bis[N-(1 -napthyl)-N-phenylamino]biphenyl (NPB), 4,4'4"-tri (N- carbazolyl)triphenylamine (TcTa) and the like.

[0050] In some embodiments, the electron-transport layer may comprise at least one electron-transfer material. Suitable electron transport materials that can be included in the electron transport layer include, but are not limited to, an optionally substituted compound selected from: aluminum tris(8-hydroxyquinolate) (Alq3), 2-(4- biphenylyl)-5-(4-tert-butylphenyl)-1 ,3,4-oxadiazole (PBD), 1 ,3-bis(N,N-t-butyl- phenyl)-1 ,3,,4-oxadiazole (OXD-7), 1 ,3-bis[2-(2,2'-bipyridine-6-yl)-1 ,3,4-oxadiazo-5- yl]benzene (BPY-OXD), 3-phenyl-4-(1 '-naphthyl)-5-phenyl-1 ,2,4-triazole (TAZ), 2,9- dimethyl-4,7-diphenyl-phenanthroline (bathocuproine or BCP), and 1 ,3,5-tris[2-N- phenylbenzimidazol-z-yl]benzene (TPBI). In one embodiment, the electron transport layer is Alq ₃ , PBD, phenanthroline, quinoxaline, TPBI, or a derivative or a combination thereof.

[0051] If desired, additional layers may be included in the light-emitting device. Additional layers that may be included include an electron-injection layer (EIL), a hole-blocking layer (HBL), an exciton-blocking layer (EBL), and/or a hole- injection layer (HIL). In addition to separate layers, some of these materials may be combined into a single layer. Additionally, some of these materials may be combined into other layers, e.g., an electron-blocking layer and/or an exciton- blocking layer can be combined into a hole-transport layer; or a hole-blocking layer and/or an exciton-blocking layer can be combined into an electron-transport layer.

[0052] In some embodiments, the light-emitting device can include an electron-injection layer between the cathode layer and the light-emitting layer. In some embodiments, the lowest unoccupied molecular orbital (LUMO) energy level of the material(s) that can be included in the electron-injection layer is high enough to prevent it from receiving an electron from the light-emitting layer. In some embodiments, the energy difference between the LUMO of the material(s) that can be included in the electron injection layer and the work function of the cathode layer is small enough to allow efficient electron injection from the cathode. Suitable electron injection materials that can be included in the electron injection layer include, but are not limited to, an optionally substituted compound selected from the following: aluminum quinolate (Alq ₃ ), 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1 ,3,4- oxadiazole (PBD), phenanthroline, quinoxaline, 1 ,3,5-tris[N-phenylbenzimidazol-z-yl] benzene (TPBI) a triazine, a metal chelate of 8-hydroxyquinoline such as tris(8- hydroxyquinoliate) aluminum, and a metal thioxinoid compound such as bis(8- quinolinethiolato) zinc. In one embodiment, the electron injection material is Alq ₃ , PBD, phenanthroline, quinoxaline, TPBI, or a derivative or a combination thereof.

[0053] In some embodiments, the device can include a hole-blocking layer, e.g., between the cathode and the light-emitting layer. Various suitable hole-blocking materials that can be included in the hole-blocking layer include, but are not limited to, an optionally substituted compound selected from the following: bathocuproine (BCP), 3,4,5-triphenyl-1 ,2,4-triazole, 3,5-bis(4-tert-butyl-phenyl)-4-phenyl-[1 ,2,4] triazole, 2,9-dimethyl-4,7-diphenyl-1 ,10-phenanthroline, and 1 ,1 -bis(4-bis(4- methylphenyl)aminophenyl)-cyclohexane.

[0054] In some embodiments, the light-emitting device can include an exciton-blocking layer, e.g., between the light-emitting layer and the anode. In one embodiment, the band gap of the material(s) that comprise an exciton blocking-layer is large enough to substantially prevent the diffusion of excitons. Suitable exciton- blocking materials that can be included in the exciton blocking layer include, but are not limited to, an optionally substituted compound selected from the following: aluminum quinolate (Alq ₃ ), 4,4'-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (a-NPD), 4,4'-N,N'-dicarbazole-biphenyl (CBP), and bathocuproine (BCP), and any other material(s) that have a large enough band gap to substantially prevent the diffusion of excitons.

[0055] In some embodiments, the light-emitting device can include a hole- injection layer, e.g., between the light-emitting layer and the anode. Various suitable hole-injection materials that can be included in the hole injection layer include, but are not limited to, an optionally substituted compound selected from the following: a polythiophene derivative such as poly(3,4-ethylenedioxythiophene (PEDOT)/polystyrene sulphonic acid (PSS), a benzidine derivative such as N, N, N', N'-tetraphenylbenzidine, poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine), a triphenylamine or phenylenediamine derivative such as N,N'-bis(4-methylphenyl)- N,N'-bis(phenyl)-1 ,4-phenylenediamine, 4,4',4"-tris(N-(naphthylen-2-yl)-N- phenylamino)triphenylamine, an oxadiazole derivative such as 1 ,3-bis(5-(4- diphenylamino)phenyl-1 ,3,4-oxadiazol-2-yl)benzene, a polyacetylene derivative such as poly(1 ,2-bis-benzylthio-acetylene), and a phthalocyanine metal complex derivative such as phthalocyanine copper. Hole-injection materials, while still being able to transport holes, may have a hole mobility substantially less than the hole mobility of conventional hole transport materials.

[0056] Those skilled in the art would recognize that the various materials described above can be incorporated in several different layers depending on the configuration of the device. In one embodiment, the materials used in each layer are selected to result in the recombination of the holes and electrons in the light-emitting layer. [0057] Light-emitting devices comprising the compounds disclosed herein can be fabricated using techniques known in the art, as informed by the guidance provided herein. For example, a glass substrate can be coated with a high work function metal such as ITO which can act as an anode. After patterning the anode layer, a light-emitting layer that includes at least a compound disclosed herein can be deposited on the anode. The cathode layer, comprising a low work functioning metal (e.g., Mg:Ag), can then be vapor evaporated onto the light-emitting layer. If desired, the device can also include an electron transport/injection layer, a hole blocking layer, a hole injection layer, an exciton blocking layer and/or a second light- emitting layer that can be added to the device using techniques known in the art, as informed by the guidance provided herein.

EMBODIMENTS

[0058] The following embodiments are contemplated:

Embodiment 1 . A compound represented by a formula:

wherein R ¹ is substituted carbazolyl or optionally substituted benzocarbazolyl; and

R ² , R ³ , and R ⁴ are independently optionally substituted carbazolyl or optionally substituted benzocarbazolyl.

Embodiment 2. The compound of embodiment 1 , wherein each substituent of R ¹ , R ² , R ³ , and R ⁴ , if present, has a molecular weight of 15 Da to 500 Da, and is represented by a formula: Co-i5Ho-350o-2No-2Clo-iFo-5-

Embodiment s. The compound of embodiment 2, wherein R ¹ is R ¹ -X, wherein R ¹ is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is C-i-6 alkyl, optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl.

Embodiment 4. The compound of embodiment 4, wherein X is unsubstituted phenyl.

Embodiment 5. The compound of embodiment 1 , wherein R ¹ is:

Embodiment 6. The compound of embodiment 1 , 2, 3, 4, or 5, wherein R ² is R ² - X, wherein R ² is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is Ci _-6 alkyl, optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl.

Embodiment 7. The compound of embodiment 6, wherein X is unsubstituted phenyl.

Embodiment 8. The compound of embodiment 1 , 2, 3, 4, or 5, wherein R ² is:

Embodiment 9. The compound of embodiment 1 , 2, 3, 4, 5, 6, 7, or 8, wherein R ³ is R ³ -X, wherein R ³ is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is C-i-6 alkyl, optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl.

Embodiment 10. The compound of embodiment 9, wherein X is unsubstituted phenyl.

Embodiment 1 1 . The compound of embodiment 1 , 2, 3, 4, 5, 6, 7, or 8, wherein R ³ is:

Embodiment 12. The compound of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1 1 , wherein R ⁴ is R ⁴ -X, wherein R ⁴ is optionally substituted carbazolyl or optionally substituted benzocarbazolyl, and X is C1-6 alkyl, optionally substituted phenyl, optionally substituted diphenylamino, optionally substituted carbazolyl, or optionally substituted phenoxazolyl.

Embodiment 13. The compound of embodiment 12, wherein X is unsubstituted phenyl.

Embodiment 14. The compound of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1 1 , wherein R ⁴ is:

Embodiment 15. The compound of embodiment 1 , wherein the compound is:

Embodiment 16. A light-emitting element comprising the compound of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, or 15.

Embodiment 17. A light-emitting device comprising the light-emitting element of embodiment 16.

Embodiment 18. An organic light-emitting diode device comprising:

a cathode;

an anode; and a light-emitting layer disposed between, and electrically connected to, the anode and the cathode, wherein the light-emitting layer comprises a compound according to embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, or 15.

Embodiment 19. The device of embodiment 18, wherein the compound is an emissive dopant, and is dispersed in a host in the light-emitting layer.

Embodiment 20. The device of embodiment 18 or 19, further comprising a hole- transport layer between the anode and the light-emitting layer and an electron- transport layer between the cathode and the light-emitting layer.

Embodiment 21 . The device of embodiment 18, 19, or 20, wherein the light- emitting layer contains less than 0.1 % w/w of noble metals.

EXAMPLES

Example 1 :

Chemical Formula: C^f-^Fe^

Exact Mass: 1482.50

[0059] 9,9 ^, ,9 ^,, ,9 ^,,, -(3,6-bis(trifluoromethyl)benzene-1 ,2,4,5- tetrayl)tetrakis(3,6-diphenyl-9H-carbazole) (EC-1 ): To a mixture of 1 ,2,4,5- tetrafluoro-3,6-bis(trifluoromethyl)benzene (0.286 g, 1 .0 mmol) (Synquest Laboratory, Alachua, FL), 3,6,-diphenyl-9/-/-carbazole (1 .5 g, 4.5 mmol) (TCI America, Portland, OR) in anhydrous tetrahydrofuran (THF) (15 mL) (Aldrich, St Louis, MO), was added sodium hydride (60% in mineral oil, 0.20 g, 5 mmol) (Aldrich) at 0 °C. The resulting mixture was stirred at 0 °C for 30 min, then 60 °C for 15 hours on a hot plate with a silicone oil bath. Yellow precipitate formed, and the mixture was diluted with 200 mL of THF, washed with brine, dried over Na ₂ S0 ₄ (Aldrich), loaded on silica gel (Aldrich, Grade 135) and purified by flash column using eluents of dichloromethane/hexanes (30% to 60%) (Aldrich). The desired fractions were collected, concentrated and filtered to give a yellow solid (EC-1 ) (0.57 g, in 40% yield). Confirmed by liquid-chromatograph-mass-spectrometer (LCMS) (using atmospheric pressure chemical ionization [APCI]) (Shimadzu Scientific Instruments, Tokyo, Japan): calculated for C ₀₄ H ₆₅ F ₆ N ₄ (M+H): 1483; found: 1483.

Synthesis of OSC-3:

p he nylboron ic acid

3 ,6-d ibromo-9H -carbazole ^63%

3,6-diphenyl-9H-carbazole

OSC-3

[0060] 3,6-diphenyl-9H-carbazole (OSC-3): A mixture of 3,6-dibromo-9H- carbazole (3.0 g, 9.2 mmol) (Aldrich), phenylboronic acid (3.0 g, 25 mmol) (Aldrich), tetrakis(triphenylphosphine)palladium (Pd(PPh ₃ ) ₄ ) (0.3 g, 0.26 mmol) (Frontier Scientific, Logan, UT) and potassium carbonate (6.5 g, 47 mmol) (Aldrich) in dioxane/water (75 mL/15 mL) (Aldrich) was degassed with bubbling argon (Airgas, San Marcos, CA) for 60 min and heated at about 100 °C on a hot plate with a silicone oil bath for about 16 hours. Upon cooling to room temperature, the whole mixture was mixed with ethyl acetate (Aldrich) and rinsed with brine. Then, the organic mixture was dried over Na ₂ S0 ₄ (Aldrich), loaded on silica gel (Grade 135) and purified by flash column using eluents of ethyl acetate/hexanes (10% to 30%) (Aldrich). After removal of solvents, a white solid (Compound OSC-3) was obtained (2.1 g, in 63% yield). Confirmed by ¹ HNMR (Jeol Instruments, Peabody, MA).

Example 2:

[0061] The following intermediates have been prepared, which can be used to prepare additional subject compounds.

Synthesis of OSC-6:

3-bromo-9-tosyl-9 - -carbazole

IC-1

[0062] 3-bromo-9-tosyl-9H-carbazole (Intermediate Compound 1 [IC- 1]): Mixture of 3-bromocarbazole (12.3 g, 0.05 mol) (Aldrich), potassium hydroxide (KOH) (3.92 g, 0.07 mol) (Aldrich) was dissolved in acetone (100 mL). Then to the solution, tosyl chloride (13.3 g, 0.07 mol) was added slowly at room temperature, then heated to reflux for 3 hours. The resulting mixture was then poured into stirring water (300 mL) while still hot. The mixture was then stirred for 30 min. The mixture next underwent filtration, the resulting solids were then washed with 200 mL methanol (Alfa Aesar), dried, and re-dissolved in dichloromethane (200 mL) for extraction. After filtration, to the solution was added to methanol (100 mL), then solvent was removed, reducing the solution to 50 mL, forming a white precipitate. The organic was then dried over Na ₂ S0 ₄ , loaded on silica gel (Grade 135) and purified by flash column using eluents of ethyl acetate/hexanes (10% to 30%). After filtration and drying in air, the product was then collected to yield a white solid comprising IC-1 was obtained (16.3g, in 82% yield). Confirmed by ¹ HNMR.

9-tosyl-9/-/-3,9'-bicarbazole

IC-2

[0063] 9-tosyl-9H-3,9'-bicarbazole (IC-2): A mixture of 3-bromo-9-tosyl- 9H-carbazole or IC-1 (2.0 g, 5 mmol), 9H-carbazole (1 .6 g, 10 mmol) (Aldrich), copper iodide (Cul) (0.19 g, 1 mmol) (Aldrich), 1 ,2-diamino-cyclohexane (0.12 g, 1 .0 mmol) (Aldrich), K ₃ P0 ₄ (2.3 g, 10 mmol) (Aldrich) in 1 ,4-dioxane (40 mL) (Aldrich) was degassed with bubbling argon for 1 hour at room temperature, then heated at 120° C for 64 hours on a hot plate with a silicone oil bath. The resulting mixture was then mixed with ethyl acetate, rinsed with brine, and then loaded on silica gel (Grade 135) to dry. Then the mixture was purified by flash chromatography using eluents of dichloromethane/hexanes (15% to 25%). The desired fractions were collected, concentrated and recrystallized in dichloromethane/methanol to give a white solid comprising IC-2 (2.25 g, in 92% yield). Confirmed by ¹ HNMR.

IC-2

[0064] 9H-3,9'-bicarbazole (OSC-6): To a solution of 9-tosyl-9H-3,9'- bicarbazole or IC-2 (8.6 g, 17.6 mmol) in THF (150 mL) and methanol (60 mL), was added sodium hydroxide aqueous solution (10 g in 60 mL water). The mixture was heated at 80 °C for 24 hours on a hot plate with a silicone oil bath. The resulting mixture was mixed with ethyl acetate and rinsed with brine, then loaded on silica gel (Grade 135) and purified by flash chromatography using eluents of ethyl acetate/hexanes (0% to 10%). After removal of solvents, the product was then collected to yield a white solid (Compound OSC-6) (5.0 g, in 86% yield). Confirmed by ¹ HNMR.

Synthesis of OSC-7:

3,6-dibromo-N-tosylcarbazole

IC-3

[0065] 3,6-dibromo-N-tosylcarbazole (IC-3): To a solution of 3,6- dibromocarbazole (16.25 g, 50 mmol) (Aldrich), and potassium hydroxide (3.93 g, 70 mmol) in anhydrous acetone (100 mL) (Alfa Aesar, Ward Hill, MA), tosyl chloride (13.35 g, 70 mmol) was added in 4 g portions at room temperature. The reaction was then heated at reflux for about 3 hours. The resulting mixture was then poured into stirring water (300 mL) while still hot. The precipitate was filtered, washed with methanol, and dried. It was then recrystallized from dichloromethane/methanol to give composition IC-3 as a white solid, 20.6g, 82% yield. Confirmed by ¹ HNMR.

3,6-bis(N-carbazolyl)-N-tosylcarbazole

IC-4

[0066] 3,6-bis(N-carbazolyl)-N-tosylcarbazole (IC-4): A mixture of IC-3 (10.00 g, 20.87 mmol), carbazole (13.37 g, 79.93 mmol) (Aldrich), Cul (1 .59 g, 8.33 mmol), frans-diaminocyclohexane (1 .0 mL, 8.34 mmol) (Aldrich), and potassium phosphate (19.21 g, 90.51 mmol) in anhydrous dioxane (165 mL) (Alfa Aesar) was degassed with bubbling argon for 2 hours at room temperature. The mixture was then heated at about 120°C for about 16 hours on a hot plate with a silicone oil bath. An aqueous workup was performed with ethyl acetate and brine, dried with magnesium sulfate. A silica gel plug (Grade 135) was run to remove the copper catalyst, using dichloromethane as the eluent. The semi-crude product was then purified by silica gel (Grade 135) column using dichloromethane/hexanes eluent in a linear gradient of 25% to 70%, holding at 70% until the product fully eluted. The product fractions were then recrystallized twice from dichloromethane in methanol to yield composition IC-4 as a white solid, 7.3g, 54% yield. Confirmed by LCMS (APCI): calculated for C43H30N3O2S (M+H): 652; Found: 652.

[0067] 3,6-bis(N-carbazolyl)carbazole (OSC-7): To a solution of IC-4 in TNF/methanol (90 mL/35 mL), sodium hydroxide (6.08 g, 151 .93 mmol) dissolved in water (35 mL) was added, and the resulting mixture was heated at about 80 °C for about 18 hours on a hot plate with a silicone oil bath. An aqueous workup was performed with ethyl acetate and brine, and was dried with magnesium sulfate. The material was purified by recrystallization by dissolving in dichloromethane and adding an equal volume of methanol before concentrating. The resulting solid was collected to yield OSC-7 as a white solid, 4.3g, 80% yield. Confirmed by LCMS (APCI): calculated for C ₃ 6H ₂ N3 (M+H): 498; Found: 498.

Synthesis of OSC-10:

2-napt hyl boroni c aci d

2-brom

OSC-10

2-napthyl boroni c aci d

2-bromo

2-(2-nitrophenyl)naphthalene

IC-5

[0068] 2-(2-nitrophenyl)naphthalene (IC-5): A mixture of 2- bromonitrobenzene (10.00 g, 49.5 mmol, 1 .00 eq), 2-napthylboronic acid (14.05 g, 81 .68 mmol, 1 .65 eq), tetrakis(triphenylphosphine)palladium (Pd(PPh ₃ ) ) (4.0 g, 3.47 mmol, 0.07 eq) (Frontier Scientific), and 1 ,4-dioxane (400 mL) were degassed with bubbling argon for about 1 hour at room temperature. Aqueous potassium carbonate (K ₂ CO ₃ ) (27.37g, 198.0 mmol, 4.0 eq K ₂ CO ₃ in 80.0mL of water) was then added and the reaction mixture was then heated to about 100 °C overnight on a hot plate with a silicone oil bath, maintaining an argon atmosphere. An aqueous workup was performed using ethyl acetate, water, and brine, and the organic phase was dried by magnesium sulphate. The crude material was then purified twice by flash chromatography on a silica gel column (Grade 135) using eluents of 10% to 50% dichloromethane in hexanes, and then 15% to 30% dichloromethane in hexanes. The product fractions were concentrated to yield Compound 3 (10.88g, 69%) as a white so ¹ HNMR.

IC-5 OSC-10

[0069] 11 H-benzo[a]carbazole (OSC-10): To a solution of 2-(2- nitrophenyl)naphthalene (IC-5) (10.88 g, 43.65 mmol) in 1 ,2-dichlorobenzene (60 mL) was added triethylphosphite (60 mL, 384.57 mmol) (Aldrich). The solution was heated at about 150 °C on a hot plate with a silicone oil bath for about 15 hours. After removal of solvent and excess reagent by vacuum distillation, the crude material was purified by column chromatography on a silica gel column (Grade 135) using eluents of 15% to 35% dichloromethane in hexanes. The product fractions were dried by rotary evaporation and recrystallized from dichloromethane/hexanes to yield Compound 4 (2.70 g, in 69% yield) as a white solid (OSC-10). Confirmed by ¹ HNMR.

Synthesis of OSC-12: 2-bromonitrobenzene

IC-6

[0070] 1 -(2-nitrophenyl)naphthalene (IC-6) A mixture of 2- bromonitrobenzene (10.00 g, 49.5 mmol, 1 .00 eq) (Aldrich), 1 -napthylboronic acid (16.18 g, 94.0 mmol, 1 .90 eq) (Aldrich), tetrakis(triphenylphosphine)palladium (Pd(PPh ₃ ) ) (4.0 g, 3.47 mmol, 0.07eq), and 1 ,4-dioxane (400 mL) were degassed with bubbling argon for about 1 .5 hours at room temperature. Aqueous potassium carbonate (K ₂ C0 ₃ ) (27.37g, 198.0 mmol, 4.0 eq K ₂ C0 ₃ in 80.0ml_ of water) was then added and the reaction was degassed with argon for about an additional 30 min. The reaction mixture was then heated to about 90 °C overnight on a hot plate with a silicone oil bath, maintaining an argon atmosphere. Once complete and cooled to room temperature, an aqueous workup was performed using ethyl acetate, water, and brine, and the organic phase was dried by magnesium sulphate. The crude material was then purified by flash chromatography using the following eluent gradient (% dichloromethane in hexanes over column volumes (CV)): linear from 10% to 15% over 7CV, linear from 15% to 20% over 2CV, isocratic at 20% until the product was fully eluted. The product fractions were concentrated to yield desired compound (12.0 g, in 76% yield) as a light yellow solid (IC-6). Confirmed by LCMS and ¹ HNMR.

7/-/-benzo[c]carbazole

IC-6 OSC-12

[0071] 7H-benzo[c]carbazole (OSC-12): To a solution of 1 -(2- nitrophenyl)naphthalene (4.5 g, 18 mmol) (IC-6) in 1 ,2-dichlorobenzene (20 mL) was added tnethylphosphite (P(OC ₂ H ₅ ) ₃ ) (20 mL, 144 mmol). The solution was heated at about 150 °C on a hot plate with a silicone oil bath for about 15 hours. After removal of the solvent and excess reagent by vacuum distillation, the remaining mixture was dissolved in dichloromethane/hexanes (20 mL/20 mL) and purified by flash column using eluents of hexanes to hexanes/dichloromethane (4:1 ). The desired fractions were collected, concentrated, loaded on silica gel (Grade 135) and purified by flash column again using eluents of dichloromethane/hexanes (10% to 20%). Removal of solvents gives a white solid (OSC-12) (2.70 g, in 69% yield). Confirmed by ¹ HNMR.

[0072] The compounds in the Table below are prepared using method described in Example 1 using the precursors shown.

Example 3:

[0073] The physical properties of the composition created in Example 1 (EC-1 ) were determined. First, 2 mg of the compound EC-1 was dissolved in 1 mL of 2-methyltetrahydrofuran (2-MeTHF) (Aldrich) and then the resulting solution was transferred into quartz tube. Then the quartz tube containing the mixture was frozen (77 K) by liquid nitrogen (Airgas) prior to measurement. Triplet (T-i) energy was measured by phosphorescent emission spectrum at 77 K, using Fluoromax-3 spectrophotometer (Horiba Instruments, Irvine CA). Table 1 depicts the physical properties associated with EC-1 (Example 1 ).

TABLE 1 : Physical data of the emissive material.

Example 4:

[0074] A light-emitting device containing the emitting compound created in Example 1 (EC-1 ) was fabricated in the following manner. The ITO substrates having sheet resistance of about 14 ohm/sq were cleaned ultrasonically and sequentially in detergent, water, acetone and then I PA; and then dried in an oven at about 80 °C for about 30 min under ambient environment. Substrates were baked at about 200 °C for about 1 hour in an ambient environment, then under UV-ozone treatment for about 30 min. PEDOT:PSS (hole-injection material) was then spin- coated on the annealed substrate at about 4000 rpm for about 30 sec. The coated layer was then baked at about 100 °C for 30 min in an ambient environment, followed by baking at 200 °C for 30 min inside a glove box (N ₂ environment). The substrate was then transferred into a vacuum chamber, where N, N'- bis(naphthalene-1 -yl)-N, N'-bis(phenyl)-benzidine (NPB) [hole-transporting material]) was vacuum deposited at a rate of about 0.1 nm/s rate under a base pressure of about 2 x 10 ^"7 torr. 1 ,3-bis(carbazol-9-yl)benzene (mCP) [electron-blocking layer] was then deposited on top of the NPB layer at a rate of about 0.1 nm/s rate. Emitting compound EC-1 (6 wt%) was then co-deposited as an emissive layer with host material 5,5'-bis(4-(9H-carbazol-9-yl)phenyl)-3,3'-bipyridine (see United States Patent No. 8,062,772, issued November 22, 201 1 ) at about 0.01 nm/s and about 0.10 nm/s, respectively, to make the appropriate thickness ratio. 2,8- bis(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) [electron-transporting material] was then deposited at about 0.1 nm/s rate on the emissive layer. A layer of lithium fluoride (LiF) (electron-injection material) was deposited at about 0.005 nm/s rate followed by deposition of the cathode as Aluminium (Al) at about 0.3 nm/s rate. The representative device structure was: ITO (about 1 10 nm thick) / PEDOT:PSS (about 30 nm thick) / NPB (about 40 nm thick) / mCP (about 10 nm thick) / EC-1 : Host (about 30 nm thick) / PPT(about 40 nm thick) / LiF (about 0.8 nm thick) / Al (about 70 nm thick). The device was then immediately encapsulated with a glass cap to cover the emissive area of the OLED device in order to protect from moisture, oxidation or mechanical damage inside a glove box.

Example 5:

[0075] The device built in Example 4 was characterized. All spectra were measured with an PR670 spectroradiometer (Photo Research, Inc., Chatsworth, CA- ) and l-V-L characteristics were taken with a Keithley 2400 SourceMeter (Keithley Instruments, Inc., Cleveland, OH-). All device operation was performed inside a nitrogen-filled glove-box.

[0076] The device fabricated in accordance with Example 3, was tested to determine the emissive qualities of the device by examining the current density and luminance as a function of the driving voltage. Various characteristics including the external quantum efficiency (EQE), luminous efficiency (LE) and power efficiency (PE) of the device at 1000 cd/m ² are shown in Table 2.

[0077] The chromaticity and efficiency measurements were performed with Otsuka Electronics MCPD 7000 multi channel photo detector system together with required optical components such as optical fibers (Otuka Electronics, Osaka, Japan), 12-inch diameter integrating spheres (Gamma Scientific, San Diego, CA, GS0IS12-TLS), calibration light source (Gamma Scientific, GS-IS12-OP1 ) configured for total flux measurement, and excitation light source (Cree, Durham, N.C., blue- LED chip, dominant wavelength 455[452]nm, C455EZ1000-S2001 ).

[0078] A blue LED with peak wavelength of 452 nm was then placed at the central position of the integrating sphere and was operated with a drive current of 25 mA. First the radiation power from the bare blue LED chip as excitation light was acquired. The light-emitting face distance of LED chip was 1 mm. A 15 mm X 15 mm thin film covered glass substrate was then mounted a distance of about 100 μιη from LED chip. The radiation power of the combination of the thin film and the blue LED was then acquired.

[0079] The PLQY of the thin film can be expressed by the following formula:

Wavelength Conversion Efficiency

Equation 1 ,

where at any wavelength λ, P _exc (A) is the radiation power of the excitation spectrum that is incident on the thin film layer and P _em i(A) is the radiation power in the combined spectrum of emission from the thin film layer and the excitation light. Therefore, the data of chromaticity can be given from MCPD data directly. A PLQY value acquired is shown in Table 2.

TABLE 2: Device Characteristics

[0080] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0081] The terms "a," "an," "the" and similar referents used in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of any claim. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0082] Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or other reasons. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

[0083] Certain embodiments are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, the claims include all modifications and equivalents of the subject matter recited in the claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.

[0084] In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the claims. Other modifications that may be employed are within the scope of the claims. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the claims are not limited to embodiments precisely as shown and described.