Organic electroluminescent materials and devices

1. A compound of Formula I:

wherein rings R A , R B , R C and R D are each independently an unsubstituted or substituted 5- or 6-membered monocyclic or polycyclic aromatic ring.

2. The compound of claim 1 , wherein at least one of rings R A , R B , R C and R D is a 6-membered aromatic ring.

3. The compound of claim 1 , wherein the compound of Formula I is selected from the group consisting of:

4. The compound of claim 1 , wherein at least one of rings R A , R B , R C and R D is a 5-membered aromatic ring.

5. The compound of claim 1 , wherein the compound of Formula I is selected from the group consisting of:

6. A compound of Formula II:

wherein rings R A , R B and R C are each independently an unsubstituted or substituted 5- or 6-membered monocyclic or polycyclic aromatic ring, and at least one of rings R A , R B and R C is a 5-membered aromatic ring.

7. The compound of claim 6 , wherein at least one of rings R A , R B and R C is a 6-membered aromatic ring.

8. The compound of claim 6 , wherein the compound of Formula II is selected from the group consisting of:

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

an anode;

a cathode; and

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

wherein rings R A , R B , R C and R D are each independently an unsubstituted or substituted 5- or 6-membered aromatic, heteroaromatic or polycyclic ring, and for the compounds of Formula II at least one of rings R A , R B and R C is a 5-membered aromatic ring.

10. The OLED of claim 9 , wherein the organic layer is an emissive layer and the compound of Formula I or Formula II is a host.

11. The OLED of claim 9 , wherein the organic layer is an emissive layer and the compound of Formula I or Formula II is an emitter.

12. The OLED of claim 9 , wherein the organic layer further comprises a phosphorescent emissive dopant; wherein the emissive dopant is a transition metal complex having at least one ligand or part of the ligand if the ligand is more than bidentate selected from the group consisting of:

wherein each X 1 to X 13 are independently selected from the group consisting of carbon and nitrogen;

wherein X is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO 2 , CR′R″, SiR′R″, and GeR′R″;

wherein R′ and R″ are optionally fused or joined to form a ring;

wherein each R a , R b , R c , and R d may represent from mono substitution to the possible maximum number of substitution, or no substitution;

wherein R′, R″, R a , R b , R c , and R d 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; and

wherein any two adjacent substituents of R a , R b , R c , and R d are optionally fused or joined to form a ring or form a multidentate ligand.

13. The OLED of claim 9 , wherein the organic layer is a blocking layer and the compound of Formula I or Formula II is a blocking material in the organic layer.

14. The OLED of claim 9 , wherein the organic layer is a transporting layer and the compound of Formula I or Formula II is a transporting material in the organic layer.

15. The OLED of claim 9 , wherein the OLED is incorporated into a device selected from the group consisting of a consumer product, an electronic component module, and a lighting panel.