Donor-acceptor polythiophene copolymers with tunable acceptor content for photoelectric conversion devices

The synthesis and characterization of a new series of substituted polythiophenes containing an electron acceptor anthraquinone moiety in the side chain are reported. The acceptor molar content was varied by the co-polymerization of both alkylthiophene and thiophene bearing anthraquinone monomers in different ratios. NMR analysis shows a good correlation between the monomer feed composition at the beginning of the polymerization and the actual unit composition of the backbone. The conjugation length and the chemical composition of the copolymers as a function of the molecular weight have been studied by size exclusion chromatography. Small angle X-ray scattering and UV-Vis absorption spectra have been used to monitor the degree of order and chain organization in the solid state. The materials exhibit a lamellar organization, in which the anthraquinone units of neighboring side chains are also organized to some degree in layered structures parallel to the polythiophene main chains. The photoluminescence measurements in solution suggest that, upon photoexcitation of the polythiophene backbone, the anthraquinone moieties act as electron acceptors and the conjugated backbone as electron donor. The tunability of the donor-acceptor ratio and the morphology in the solid state make these photoactive copolymers interesting candidates for organic photoelectric conversion devices.