Tailoring Chain-Edge C=R (R = C, O, S) Microenvironments in sp2-Carbon-Bridged 1D COFs Unlocks a ‘Moderate Balance’ Effect for Photocatalytic H2O2 Production

One-dimensional covalent organic frameworks (1D COFs) featuring double-chain architectures offer abundant exposed active sites for photocatalysis. However, topological constraints and entropy-driven stacking disorder severely impede their controllable synthesis, obscuring definitive structure–activity relationships. Herein, we report a series of sp2-carbon-bridged 1D COFs with atomically tailored chain-edge microenvironments (C=R-COFs, R = C, O, S) for efficient photocatalytic H2O2 production. In a water/benzyl alcohol (9:1, v/v) system under an O2 atmosphere, C=S-COF exhibited the highest H2O2 production rate of 3750.7 μmol g-1 h-1, corresponding to 1.8- and 20.0-fold enhancements over C=O-COF and C=C-COF, respectively, ranking among the best reported 1D COFs. Combined experimental and theoretical calculations reveal that the superior activity of C=S-COF stems not only from its red-shifted light harvesting (up to 810 nm), prolonged exciton lifetime, and supplementary 1O2-mediated pathway, but more critically, from an interfacial "moderate balance" effect. Specifically, endowing the chain-edge active sites with intermediate local charge density and moderate hydrophilicity reconciles competing elementary steps—simultaneously optimizing interfacial wetting, reactant (O2/H2O) activation, and H2O2 desorption, rather than maximizing a single descriptor. The “moderate balance” effect offers a new design paradigm for the development of advanced COF photocatalysts.