Carbene metal complexes as OLED materials

1. A compound comprising a metal center and a ligand coordinated to the metal center, wherein the ligand is selected from:

wherein R 1 and R 2 are independently selected from hydrogen, alkyl, alkenyl, alkynyl, aralkyl, CN, CF 3 , CO 2 R′, C(O)R′, C(O)NR′ 2 , NR′ 2 , NO 2 , OR′, SR′, SO 2 , SOR′, SO 3 R′, halo, aryl, heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclic group;

R 3 is selected from hydrogen, alkyl, alkenyl, alkynyl, aralkyl, aryl, heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclic group;

additionally or alternatively, two R groups on the same or adjacent ring, together form a 5 or 6-member cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; and wherein said cyclic group is optionally substituted by one or more substituents J;

each substituent J is independently selected from the group consisting of R′, CN, CF 3 , C(O)OR′, C(O)R′, C(O)NR′ 2 , NR′ 2 , NO 2 , OR′, SR′, SO 2 , SOR′, or SO 3 R′, and additionally, or alternatively, two J groups on adjacent ring atoms form a fused 5- or 6-membered aromatic group;

each R′ is independently selected from H, halo, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl;

a is 0, 1, 2, 3, or 4; and b is 0, 1, 2, or 3.

2. The compound of claim 1 , wherein the metal center is Ir or Pt.

3. The compound of claim 2 , wherein the metal center is Ir.

4. The compound of claim 1 , wherein each of R 1 is H or an alkyl having 1-15 carbons; each of R 2 is H or an alkyl having 1-15 carbons; each of R 3 is H or an alkyl having 1-15 carbons.

5. The compound of claim 1 , wherein the compound is:

wherein M is the metal center;

(X—Y) is a photoactive ligand or an ancillary ligand;

m is a value from 1 to the maximum number of ligands that may be attached to metal M;

m+n is the maximum number of ligands that may be attached to metal M.

6. The compound of claim 5 , wherein M is selected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te, Al, Ge, Au, and Ag.

7. The compound of claim 5 , wherein M is Ir or Pt.

8. The compound of claim 7 , wherein M is Ir.

9. The compound of claim 8 , wherein m is 3 and n is 0.

10. The compound of claim 5 , wherein each of R 1 is H or an alkyl having 1-15 carbons; each of R 2 is H or an alkyl having 1-15 carbons; each of R 3 is H or an alkyl having 1-15 carbons.

11. The compound of claim 5 , wherein the compound is:

and a is 0, 1, 2, or 3.

12. An organic light emitting device comprising:

an anode;

a cathode; and

an organic layer between the anode and the cathode, the organic layer comprising the compound of claim 1 .

13. The device of claim 12 , wherein the metal center is Ir or Pt.

14. The compound of claim 13 , wherein the metal center is Ir.

15. The compound of claim 12 , wherein each of R 1 is H or an alkyl having 1-15 carbons; each of R 2 is H or an alkyl having 1-15 carbons; each of R 3 is H or an alkyl having 1-15 carbons.

16. The device of claim 15 , wherein the organic layer is an emissive layer.

17. The compound of claim 1 , wherein the ligand is:

and a is 0, 1, 2, or 3.