Four donor–acceptor (D-A) copolymers of 2,3-difunctionalized thieno[3,4-b]pyrazine (TP) and 9,9-dioctylfluorene were prepared in order to illustrate the ability to tune the electronic and optical properties of TP-based D-A polymers by the choice of side chains on the TP unit. In addition, analogous polymers were prepared with and without thiophene spacer units in order to allow discussion of their effect on the material properties. This combination of effects allowed tuning of the band gap over the range of 1.6–2.1 eV. Full optical and electrochemical characterization is reported for all materials, as well as initial photovoltaic device data for representative materials.