The processability and the solubility of organic materials are important in the fabrication of photoelectric conversion devices. A powerful strategy for chemical modification and for electronic property control of polymeric materials is the copolymerisation of different monomers. Polydithienothiophenes that exhibit low energy gap are promising materials for photovoltaic applications. To overcome their low processability we have designed copolymers containing either dithienothiophene or dithienothiophene-S,S-dioxide monomers in the backbone. The synthesis of these soluble copolymers is presented. Their use as photoactive materials in blends with buckminsterfullerene C-60 or with TiO2 is discussed in terms of photo-induced charge transfer, probed by photoluminescence and photo-induced absorption measurements.