Organic electroluminescent materials and devices

A compound having the structure ofis disclosed. In the structure of Formula I, each of R1, R2, and R3 is independently a hydrogen, a non-fused aryl group having one meta-substituent, or a non-fused heteroaryl six-membered ring having one or more meta-substituents; each meta-substituent is a non-fused aryl or non-fused heteroaryl six-membered ring optionally substituted with further substituents selected from the group consisting of non-fused aryl groups, non-fused heteroaryl groups, and alkyl groups; and at least one of R1, R2, and R3 is a non-fused aryl having one meta-substituent or a heteroaryl six-membered ring having at least one meta-substituent, wherein each meta-substituent is a non-fused aryl or non-fused heteroaryl group further substituted with a chain of at least two non-fused aryl or non-fused heteroaryl groups. The compounds may be useful in phosphorescent organic light emitting devices.