Developments in the chemistry and band gap engineering of donor–acceptor substituted conjugated polymers

This paper reviews the tools to manipulate and minimize the band gap of conjugated (co)polymers. The effects of minimization of the bond length alternation and of the incorporation of donor-π-acceptor units are discussed in particular. A systematic study of a series of alternating donor–acceptor oligomers has revealed the achievable limits and allowed for a prognosis of the performance of corresponding copolymers. The decisive influence of the LUMO eigenvectors of the acceptors on the band gap is highlighted. A new synthesis of benzo[1,2-c:4,5-c]bis[1,2,5]thiadiazole containing donor–acceptor monomers and their acid-catalyzed polymerization are described. Finally, band gap tuning by appropriate substitution, conformational adjustment and mesoscopic ordering is discussed.