Thiophene- and selenophene-based conjugated polymeric mixed ionic/electronic conductors

Mixed ionic/electronic conductors (MIECs) are desirable materials for next-generation electronic devices and energy storage applications. Polymeric MIECs are attractive from the standpoint that their structure can be controlled and anticipated to have mechanically robust properties. Here, we prepare and investigate conjugated copolymers containing thiophene and selenophene repeat units and their homopolymer counterparts. Specifically, thiophene bearing a triethylene glycol (EG₃) side chain was polymerized and copolymerized with dodecyl thiophene/selenophene monomers. The synthesis leads to a class of copolymers that contain either S or Se and are blocky in nature. The Li-ion conductivity of ionically doped copolymers, P3DDT-s-P3(EG₃)T and P3DDS-s-P3(EG₃)T (9.7 × 10⁻⁶ and 8.2 × 10⁻⁶ S/cm, respectively), was 3–4 fold higher than that of the ionically doped constituent homopolymer, P3(EG₃)T (2.2 × 10⁻⁶ S/cm), at ambient conditions. The electronic conductivity of the oxidatively doped copolymers was significantly higher than that of the constituent homopolymer P3(EG₃)T, and most notably, P3DDS-s-P3(EG₃)T reached ∼7 S/cm, which is the same order of magnitude as poly(3-dodecylthiophene) and poly(3-dodecylselenophene), which are the highest oxidatively doped conductors based on control experiments. Our findings provide implications for designing new MIECs based on copolymerization and the incorporation of heavy atom heterocycles.