New head-to-head type polythiophenes with acetylenic -C equivalent to CR side groups, HH-P3(C equivalent to CR)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 lambda(max) position was red-shifted from those of regioregular poly(3-alkylihiophene)s (385 and 430 nm for HH- and HT-type polymers, respectively). These data indicate that the newly synthesized polythiophene with the -C equivalent to CR group has a highly coplanar structure with a large effective pi-conjugation system. (c) 2005 Published by Elsevier Ltd.