ORGANIC ELECTROLUMINESCENT MATERIALS AND DEVICES

1 . A formulation comprising a first compound of Formula I:

and a second compound;

wherein ring A is a 5-membered or 6-membered aromatic ring;

wherein R A , R B , and R C each independently represent mono to the maximum allowable substitution, or no substitution;

wherein Y 1 is absent or present, and when present is selected from the group consisting of a direct bond, O, S, Se, CRR′, NR, SiRR′, and BR;

wherein each X 1 -X 3 is N or CR;

wherein at least one of X 1 -X 3 is N;

wherein each A 1 -A 5 is independently C or N;

wherein the maximum number of N atoms that can connect to each other within each ring is two;

wherein each R 1 , R 2 , R 3 , and R 4 is independently selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, heteroaryl, and combinations thereof;

wherein each R, R′, R A , R B , and R C is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein any two substituents may be joined or fused together to form a ring;

wherein the second compound contains at least one of the following groups in the molecule:

wherein R 101 is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

k is an integer from 0 to 20;

X 101 to X 108 are independently selected from C (including CH) or N; and

Z 101 and Z 102 are independently selected from NR 101 , O, or S.

2 . The formulation of claim 1 , wherein each R 101 , R, R′, R A , R B , and R C is independently a hydrogen or a substituent selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.

3 . The formulation of claim 1 , wherein X 1 -X 3 are each N; or X 2 is CR, and X 1 and X 3 are N; or X 1 is N, and X 2 and X 3 are CR.

4 . The formulation of claim 1 , wherein R 1 and R 2 are joined to form a carbazole group and R 3 and R 4 are joined together to form a carbazole group.

5 . The formulation of claim 1 , wherein A 1 -A 5 are each C, Y 1 is a direct bond, ring A is a 6-membered aromatic ring that is a benzene ring.

6 . The formulation of claim 1 , wherein at least one of the first compound and the second compound is partially or fully deuterated.

7 . The formulation of claim 1 , wherein both the first compound and the second compound are partially or fully deuterated.

8 . The formulation of claim 1 , wherein both the first compound and the second compound are fully deuterated.

9 . The formulation of claim 1 , wherein the first compound is selected from the group consisting of:

wherein R D , R E , R F , R G and R H represent mono to the maximum allowable substitution, or no substitution;

wherein each Y 2 and Y 3 is independently selected from a group consisting of a direct bond, O, S, Se, CRR′, NR, SiRR′, and BR, or it is not present;

wherein A 6 to A 25 are each independently C or N;

wherein the maximum number of N atoms that can connect to each other within each ring is two;

wherein Z 1 to Z 3 are each independently selected from a group consisting of O, S, Se, CRR′, NR, SiRR′, or BR;

wherein each R D , R E , R F , R G and R H is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and

wherein any two substituents may be joined or fused together to form a ring.

10 . The compound of claim 9 , wherein each R A , R B , R D , R E , R F , R G and R H is hydrogen or deuterium;

each R C is independently a hydrogen or a substituent selected from the group consisting of deuterium, and heteroaryl that is a carbazole, and combinations thereof.

11 . The compound of claim 10 , wherein one R C is a carbazole, which can be partially or fully deuterated; the remaining R C is hydrogen or deuterium.

12 . The formulation of claim 1 , wherein the first compound is selected from the group consisting of Compound H1-B1-B1-B1 to Compound H50-B60-B60-B60 based on the numbering formula Hn-Bi-Bj-Bk, wherein n is an integer from 1 to 50, wherein i, j, and k are each independently an integer from 1 to 60, wherein H1 to H50 have the following structures:

or the compound is selected from the group consisting of Compound H51-B1-B1 to Compound H70-B60-B60 based on the numbering formula Hm-Bi-Bj, wherein m is an integer from 51 to 70, wherein i and j are each independently an integer from 1 to 60, wherein H51 to H70 have the following structures:

and wherein B1 to B60 have the following structures:

and

wherein the first compound can be partially or fully deuterated.

13 . The formulation of claim 1 , wherein the first compound is selected from the group consisting of:

and

wherein the first compound can be partially or fully deuterated.

14 . The formulation of claim 1 , wherein the second compound has the formula of

wherein k is 0, 1 or 2; R 101 is aryl, which can be further substituted by one or more substituents, each of which is independently selected from the group consisting and of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

15 . The formulation of claim 14 , wherein k is 2, R 101 is phenyl or biphenyl; wherein the second compound can be partially or fully deuterated.

16 . The formulation of claim 15 , wherein the first compound is

17 . The formulation of claim 16 , wherein both the first and the second compounds are fully deuterated.

18 . A formulation comprising a first compound and a second compound; wherein the first compound is a fully deuterated compound having a formula of

and the second compound is a fully deuterated compound having a formula of

wherein k is 2, R 101 is biphenyl; or

wherein the first compound is a fully deuterated compound having a formula of

and the second compound is a fully deuterated compound having a formula of

wherein k is 2, R 101 is phenyl.

19 . An organic light emitting device (OLED) comprising:

an anode;

a cathode;

and an organic layer, disposed between the anode and the cathode, comprising a formulation comprising a first compound of Formula I:

and a second compound;

wherein ring A is a 5-membered or 6-membered aromatic ring;

wherein R A , R B , and R C each independently represent mono to the maximum allowable substitution, or no substitution;

wherein Y 1 is absent or present, and when present is selected from the group consisting of a direct bond, O, S, Se, CRR′, NR, SiRR′, and BR;

wherein each X 1 -X 3 is N or CR;

wherein at least one of X 1 -X 3 is N;

wherein each A 1 -A 5 is independently C or N;

wherein the maximum number of N atoms that can connect to each other within each ring is two;

wherein each R 1 , R 2 , R 3 , and R 4 is independently selected from the group consisting of alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl, heteroaryl, and combinations thereof;

wherein each R, R′, R A , R B , and R C is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

wherein any two substituents may be joined or fused together to form a ring;

wherein the second compound contains at least one of the following groups in the molecule:

wherein R 101 is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;

k is an integer from 0 to 20;

X 101 to X 108 are independently selected from C (including CH) or N; and

Z 101 and Z 102 are independently selected from NR 101 , O, or S.

20 . The OLED of claim 19 , wherein the organic layer is an emissive layer that further comprises an emitter; wherein the emitter is selected from the group consisting of phosphorescent emitter, fluorescent emitter, delayed fluorescent emitter, and combination thereof.