Synthesis and Optoelectronic Properties of Conjugated Polymers Based on a Dithienobenzimidazole Unit in the Main Chain

Three conjugated polymers with the dithienobenzimidazole (DTBIm) unit (P1, P3, and P4) and one conjugated polymer with the dithienobenzoxazole unit (P2) were synthesized by the cross-coupling polymerization. The absorption maxima showed a red-shift in the order of P3 (406 nm), P2 (426 nm), P1 (438 nm), and P4 (450 nm), which was studied in detail using the frontier molecular orbital calculation of the model compounds. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the DTBIm unit-containing conjugated polymers were estimated by the cyclic voltammetry. The transformation from DTBIm (P4) to dithienobenzimidazolium (P4') was also carried out to shift the absorption maxima of P4' (454 nm) by promoting the intramolecular charge transfer between the DTBIm and thiophene units. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 401-409