Conjugated crystalline-crystalline donor- acceptor-donor block copolymer semiconductors, with regio-regular poly(3-hexylthiophene) as a donor (p-type) block and poly(pyridinium pheneylene) as an acceptor (n-type) block within the backbone, were produced by sequential Grignard metathesis synthesis of poly(3-hexylthiophene), a Yamamoto-type cross-coupling polymerization-cyclization sequence. These conjugated block copolymers are soluble in organic solvents and display broad optical absorption bands extending close to the near-infrared region. They show reversible ambipolar redox properties with high electron affinities of 3.8-4.0 eV as well as useful ionization potentials of 5.1 eV that are characteristic of the respective blocks. Block copolymers from p- and n-type organic semiconductors are of interest for the formation of nanostructured bulk heterojunctions in photovoltaic devices.