Highly planar charge transport channels in novel thiophene S,S-dioxide-based polymers for efficient photocatalytic CO2-to-CO conversion

Achieving efficient solar-driven CO₂ reduction (CO₂RR) into valuable carbon–neutral fuels without relying on photosensitizers, sacrificial agents, or co-catalysts has proven to be an ongoing challenge, especially for metal-free photocatalytic systems. Herein, we have developed and synthesized two innovative thiophene S,S-dioxide (TDO)-based donor (D)-acceptor (A)-type linear conjugated polymers, named TDO-T and TDO-2T, targeting CO₂ reduction using water vapor. By functionalizing thiophene with TDO, we have significantly improved the planarity of its molecular structure, which is vital for effective charge transport. Moreover, the robust D-A interactions between TDO and thiophene units enhance electron delocalization across the polymer backbone, thereby optimizing charge transfer characteristics and boosting local electron density. These factors lead to highly planar charge transmission pathways within the molecules, resulting in exceptional photocatalytic CO₂-to-CO conversion efficiencies. Impressively, TDO-2T and TDO-T achieved conversion rates of 379.35 and 229.36 μmol g^-1h⁻¹, respectively, all without the need for photosensitizers, cocatalysts, or sacrificial agents. This research marks a groundbreaking advancement in the use of TDO units, setting a new benchmark for designing high-performance photocatalysts for CO₂RR.