Naphthalimide-Based Polymeric Photocatalysts: A Versatile Platform for Low-Energy Red-Light-Driven Aqueous Chemical Transformations

Low-energy red-light catalysis has garnered increasing attention for synthetic applications, due to its strong penetration ability, high reaction selectivity, and low safety risks, yet it confronts critical material-level challenges in terms of organic photocatalysts particularly with respect to photobleaching and insufficient red-light absorption. Meanwhile, the development of greener, red-light-driven aqueous-phase synthesis encounters significant thermodynamic barriers, posing substantial challenges to its practical feasibility. Here, we report a rational design of water-compatible, red-light-responsive polymeric NI photocatalysts by integrating hydrophilic polyether chains, electron-donating thiophene units, and NI cores into a single framework architecture. The optimal polymer, poly-Thio-NI-1, exhibits high activity in water under red light for diverse organic transformations. It allows gram-scale synthesis under natural sunlight and can be reused at least five times without significant loss of activity. Mechanistic studies indicate that the reaction proceeds via an electron-transfer pathway to oxygen, generating superoxide radical anions. Theoretical calculations reveal that the enhanced performance originates from a narrowed band gap due to polymerization, improved oxygen adsorption, and increased Bader charge. This work provides a general design strategy for metal-free, red-light-absorbing polymeric photocatalysts and establishes NI-based polymers as a versatile platform for aqueous photochemical synthesis.