Electroactive materials

A compound having Formula II-a, or a compound having Formula II-b:

• wherein:
• Z is selected from the group consisting of CR4R5, C═CR4R5, SiR4R5, GeR4R5, NR4a, PR4a, P(O)R4a, O, S, SO, SO2, Se;
• SeO, SeO2, Te, TeO, and TeO2;
• R1-R3 are the same or different at each occurrence and are selected from the group consisting of D, aryl, heteroaryl, alkyl, amino, silyl, germyl, deuterated aryl, deuterated heteroaryl, deuterated alkyl, deuterated amino, deuterated silyl, and deuterated germyl, where two groups selected from R1, R2, or R3 are optionally joined together to form a fused ring;
• R4-R5 are the same or different at each occurrence and are selected from the group consisting of H, D, aryl, heteroaryl, alkyl, amino, silyl, germyl, deuterated aryl, deuterated heteroaryl, deuterated alkyl, deuterated amino, deuterated silyl, and deuterated germyl;
• R4a is selected from the group consisting of alkyl, silyl, germyl, aryl, and deuterated analogs thereof;
• a1, b, and c are the same or different and are an integer from 0-3;
• b1 and c1 are the same or different and are an integer from 0-2;
• Ar1 and Ar3 of Formulas (II-a) and (II-b) are the same or different at each occurrence and are phenyl, biphenyl, or naphthyl, each of which is unsubstituted or substituted with an alkyl having 1 to 20 carbons or carbazolyl;
• and
• Ar2 and Ar4 of Formulas (II-a) and (II-b) are the same or different at each occurrence and are phenyl, biphenyl, or naphthyl, each of which is substituted with carbazolyl.