Preparation of poly(3,3′-dialkynyl-2,2′-bithiophene-5,5′-diyl) with high coplanarity and effective π-conjugation system

New head-to-head type polythiophenes with acetylenic –CCR side groups, HH-P3(CCR)Th (R=n-C10H21, n-C6H13, n-C4H9), were prepared by palladium-catalyzed polycondensation of the corresponding dibromo-monomers by using Me3SnSnMe3 as the polycondensing agent. The single crystal structure of the monomer revealed high coplanarity of the bithiophene unit, and the derived polymer showed a UV–vis absorption peak at approximately 520 nm. The λmax position was red-shifted from those of regioregular poly(3-alkylthiophene)s (385 and 430 nm for HH- and HT-type polymers, respectively). These data indicate that the newly synthesized polythiophene with the –CCR group has a highly coplanar structure with a large effective π-conjugation system.