Direct arylation polycondensation for the synthesis of bithiophene-based alternating copolymers

Direct arylation polycondensation reactions using a simple catalytic system gave eight kinds of bithiophene-based alternating copolymers. The conditions for the reactions of 3,3′,4,4′-tetramethylbithiophene with dibromoarylenes were optimized to obtain high-molecular-weight polymers without formation of cross-linked structures. In the reaction of a dibromoarylene containing a reactive C–H bond, a short reaction time (1.5 h) was suitable for preventing side reactions. In contrast, a long reaction time (6 h) gave high-molecular-weight polymers from dibromoarylene monomers without a reactive C–H bond. This polycondensation reaction enables the synthesis of polymers containing dye structures such as diketopyrrolopyrrole and isoindigo, which are applicable as materials for polymer solar cells