¿Conjugated? Copolymers from a Pechmann Dye Derivative

Empirical observation and quantum chemical explanation of a likely common but “overlooked” outcome of the donor–acceptor (D–A) approach to organic electronic materials are reported. The frontier molecular orbitals (FMOs) of D–A copolymers prepared from the amidated Pechmann dye unit (APD) are dictated primarily by this “acceptor,” largely because its HOMO–LUMO gap falls within the gaps of common “donor” units. D–A copolymers with common benzodithiophene and cyclopentadithiophene units as “donors” are presented, giving examples having similar optical properties regardless of backbone planarity and solid-state packing motif, along with calculations extending to several other common donor monomers to indicate generality. According to quantum-chemical studies, APD-localized FMOs form the transition to the lowest excited state, and higher lying charge-transfer (CT) states. Other existing examples of this FMO situation are likely, but with (opto)electronic properties attributed to lack of conjugation due to, e.g., polymer backbone twisting. (Figure presented.).