Organic electroluminescent materials and devices

1. A compound comprising a first ligand L A having Formula I:

wherein ring B is a 5 or 6-membered carbocyclic or heterocyclic ring;

wherein R B represents mono to the possible maximum number of substitution, or no substitution;

wherein Z 2 is selected from the group consisting of carbon or nitrogen;

wherein, when ring B is a 5-membered ring, Z 1 is nitrogen or carbon, and when ring B is a 6-membered ring, Z 1 is nitrogen;

wherein A 1 , A 2 , A 3 , and A 4 are each independently CR or N;

wherein ring C is a 6 membered aromatic ring;

n is 1;

wherein A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7 , and A 8 are each independently CR, and the Rs of two adjacent A 5 , A 6 , A 7 , and A 8 are joined together to form a six-membered ring fused to ring C;

wherein X is O, S, or Se;

wherein the ligand L A is coordinated to an Ir atom;

wherein the Ir atom is bonded to ring A through an Ir—C bond;

wherein the Ir atom is also coordinated to at least one of:

(1) a ligand L B and the compound has a structure Ir(L A )(L B ) 2 , wherein L B has a structure

 wherein X 1 , X 2 , X 3 , X 4 , X 5 , X 6 , X 7 , and X 8 are C, wherein R a and R b are each 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, or

(2) a ligand L C and the compound has a formula of Ir(L A ) 2 (L C ), wherein L C has a structure

wherein Ra, Rb, and Rc are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, and combinations thereof;

wherein, when the Ir atom is coordinated to L B , Ring B is pyridine, Z 1 is nitrogen, Z 2 is carbon;

wherein each R and R B 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;

wherein any adjacent substituents are optionally joined or fused into a ring;

wherein the ligand L A is optionally linked with ligand L B or ligand L C to comprise a tetradentate or hexadentate ligand.

2. The compound of claim 1 , wherein X is O.

3. The compound of claim 1 , wherein the Rs of two adjacent A 5 , A 6 , A 7 , and A 8 are joined together to form a phenyl ring fused to ring C.

4. The compound of claim 1 , wherein the compound has formula of Ir(L A ) 2 (L C );

wherein the ligand L C is selected from the group consisting of:

5. The compound of claim 1 , wherein the ligand L A is selected from the group consisting of:

and

wherein R A and R C have the same definition as R B .

6. The compound of claim 1 , wherein the ligand L A is selected from the group consisting of:

7. The compound of claim 6 , wherein the compound has the formula Ir(L Ai ) 2 (L Ck );

and

wherein L Ck has the following formula:

8. The compound of claim 6 , wherein the compound has the formula Ir(L Ai )(L Bj ) 2 ; and wherein L Bi has the following formula:

9. The compound of claim 1 , wherein the ligand L A is selected from the group consisting of:

and

wherein R A and R C have the same definition as R B .

10. The compound of claim 1 , wherein the ligand L A is selected from the group consisting of:

11. An organic light-emitting device (OLED) comprising:

an anode;

a cathode; and

an organic layer, disposed between the anode and the cathode, comprising a compound comprising a first ligand L A having Formula I:

wherein ring B is a 5 or 6-membered carbocyclic or heterocyclic ring;

wherein R B represents mono to the possible maximum number of substitution, or no substitution;

wherein Z 2 is selected from the group consisting of carbon or nitrogen;

wherein, when ring B is a 5-membered ring, Z 1 is nitrogen or carbon, and when ring B is a 6-membered ring, Z 1 is nitrogen;

wherein A 1 , A 2 , A 3 , and A 4 are each independently CR or N;

wherein ring C is a 6 membered aromatic ring;

n is 1;

wherein A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7 , and A 8 are each independently CR, and the Rs of two adjacent A 5 , A 6 , A 7 , and A 8 are joined together to form a six-membered ring fused to ring C;

wherein X is O, S, or Se;

wherein the ligand L A is coordinated to an Ir atom;

wherein the Ir atom is bonded to ring A through an Ir—C bond;

wherein the Ir atom is also coordinated to at least one of:

(1) a ligand L B and the compound has a structure Ir(L A )(L B ) 2 , wherein L B has a structure

 wherein X 1 , X 2 , X 3 , X 4 , X 5 , X 6 , X 7 , and X 8 are C, wherein R a and R b are each 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, or

(2) a ligand L C and the compound has a formula of Ir(L A ) 2 (L C ), wherein L C has a structure

 wherein Ra, Rb, and Rc are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, and combinations thereof;

wherein, when the Ir atom is coordinated to L B , Ring B is pyridine, Z 1 is nitrogen, Z 2 is carbon;

wherein each R and R B 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;

wherein any adjacent substituents are optionally joined or fused into a ring;

wherein the ligand L A is optionally linked with ligand L B or ligand L C to comprise a tetradentate or hexadentate ligand.

12. The OLED of claim 11 , wherein the organic layer is an emissive layer and the compound is an emissive dopant or a non-emissive dopant.

13. The OLED of claim 11 , wherein the organic layer further comprises a host, wherein host comprises at least one chemical group selected from the group consisting of triphenylene, carbazole, dibenzothiophene, dibenzofuran, dibenzoselenophene, azatriphenylene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene.

14. The OLED of claim 11 , wherein the organic layer further comprises a host, wherein the host is selected from the group consisting of:

and combinations thereof.

15. A compound selected from the group consisting of: