Covalent Triazine Frameworks with Unidirectional Electron Transfer for Enhanced Photocatalytic Oxidation Reactions

In biological systems, redox-driven catalytic processes efficiently occur through controllable active sites with a clearly defined stepwise charge transfer pathway. For artificial catalytic systems, especially pure organic, polymeric, and heterogeneous photocatalysts, the main challenge lies in gaining precise control of electron transfer pathways through the catalytic active sites. Here, we design crystalline phenothiazine-anchored covalent triazine frameworks (CTFs) as a benchmark example of pure organic photocatalysts with precisely controllable unidirectional electron transfer pathways. Monofunctionalized phenothiazine units were copolymerized onto CTFs, leading to defined electron transfer within the polymer network with a strong dipole and a high built-in electric field upon light-induced charge separation. By combining in situ spectroscopic methods and transient time-dependent density functional theory calculations, we reveal that sulfur atoms on phenothiazine units were the major oxidative sites by formation of photogenerated holes. High catalytic activity, recyclability, and general applicability of the designed CTFs were demonstrated by important oxidation reactions such as oxidative coupling of primary amines, formation of benzimidazoles, oxidative formylation of N, N-dimethylanilines, and dehydration of aldoximes.