Viologen Covalent Organic Framework Mediates Near-Infrared Light-Induced Electron Transfer for Catalytic Oxidative Coupling Reactions

Near-infrared (NIR) light-driven photoreactions are advantageous over visible light-driven ones because NIR photons have lower energy and fewer side reactions, deeper penetration in reaction media, and high abundance in the solar spectrum. However, currently available covalent organic frameworks (COFs) absorb in the UV-vis region and catalyze photoreactions under blue or white light irradiation. Herein, we report a linker-to-linker charge transfer process in a viologen-linked porphyrin COF (Vio-COF), leading to a novel type of hyperporphyrin effect and extending the absorption into the NIR region with an absorption edge at 998 nm. Under NIR irradiation, photoinduced charge separation in Vio-COF generates a viologen radical that efficiently reduces oxygen to form superoxide radicals for catalytic oxidative coupling reactions. The proximity of porphyrin and viologen units within the framework significantly enhances the catalytic performance of Vio-COF, outperforming its homogeneous counterparts in aerobic oxidative amidation and amine coupling reactions. Vio-COF was readily recycled and used in six oxidative coupling reactions.