Disclosed is a compound having substructure F: wherein R′1 is a straight or branched chain of two or more non-fused aryl or non-fused heteroaryl groups substituted with Ra, wherein Ra is a non-fused aryl or non-fused heteroaryl, a branched or straight chain of non-fused aryl or a non-fused heteroaryl, or an alkyl substituted non-fused aryl or an alkyl substituted non-fused heteroaryl group. The compounds may be useful in phosphorescent organic light emitting devices.