Synthesis and Characterization of a Non-Conjugated Backbone Polymer Bearing [1]Benzothieno[3,2-b][1]benzothiophene with a Herringbone Packing Motif

Conjugated polymers encompassing delocalized π-electrons in their backbones exhibit high photoabsorption and efficient charge carrier transport through the intermolecular π-π stacking suitable for organic photovoltaics (OPV). By contrast, small molecules such as [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives, which demonstrates high field-effect transistor hole mobilities owing to their 2-dimensional herringbone packing, have not yet been applied to OPVs. Here we report a non-conjugated backbone polymer bearing phenyl- and decyl-substituted BTBT (Ph-BTBT-10) as the pendant conjugated unit, which was synthesized by ring opening polymerization of epoxy append. The polymer showed an X-ray diffraction pattern ascribed to the layered lamellar and less ordered herringbone packing. In addition, a model molecule of Ph-BTBT-10 showed charge separation upon photoexcitation when blended with a non-fullerene acceptor (ITIC) or fullerene (PCBM).