Disclosed is a compound having Formula I In Formula I: Ar is aryl or deuterated aryl; R1 and R2 are the same or different and can be alkyl, silyl, aryl, deuterated alkyl, deuterated silyl, or deuterated aryl; R3-R5 are the same or different at each occurrence and can be D, alkyl, silyl, aryl, deuterated alkyl, deuterated aryl, or deuterated silyl; where two adjacent R4 groups can be joined together to form a fused 6-membered aromatic or deuterated aromatic ring; a and c are independently an integer from 0-3; and b is an integer from 0-4.Formula I may exist as either fac or mer structural isomers including mixtures of both.