Efficient Solar‐Driven Polymerization Enabled by Triplet Excited State‐Mediated Electron Transfer in Benzothioxanthene Imide Photocatalysts

ABSTRACT Visible‐light‐driven electron transfer photoredox radical polymerization systems, comprising a photocatalyst, donor co‐initiator, and photoinitiator, are a major focus in current photochemistry and polymer chemistry. However, the electronic transfer efficiency and pathways between the excited state of the catalyst and the co‐initiator or photoinitiator remain poorly understood. In this work, we introduced through‐space charge transfer (TSCT) for the first time to modulate the visible‐light photocatalytic excited‐state properties of benzothioxanthene imide ( BTXI ), thereby synthesizing BTXI‐CZ and BTXI‐PXZ . This approach significantly enhances intersystem crossing (ISC) efficiency, excited‐state oxidative potential, and lifetime. Fluorescence quenching and transient absorption experiments confirm that the TSCT‐type photocatalyst exhibits significantly faster electron transfer rates with co‐initiators compared to conventional BTXI . This advantage stems from the highly efficient triplet excited state‐mediated electron transfer process, thereby substantially enhancing the polymerization performance of the system. Using BTXI‐PXZ as a photocatalyst, the conversion rate of acrylic resin monomers exceeded 80% within 5 s under ultra‐low‐power 450 nm visible light, demonstrating polymerization efficiency superior to that of traditional BTXI and the commercial photoinitiator 2‐isopropylthioxanthone ( ITX ). This work offers new insights into the mechanism of photoredox polymerization and provides a paradigm for designing efficient, visible‐light‐absorbing, heavy‐atom‐free photocatalysts.