Exciton Behavior Manipulated by Structural Isomers Governs H ₂ O ₂ Photosynthesis Pathway

Solar-driven H2O2 synthesis from water and oxygen holds great promise for environmentally benign and efficient chemical production. However, the complex photochemical pathways governed by exciton behavior during photoexcitation often limit both the yield and the selectivity of H2O2. Herein, structural isomers of the COFs (pBPY-COF and oBPY-COF) are employed as probes to elucidate distinct exciton behaviors. Through precise structural engineering, exciton characteristics are finely tuned, revealing clear structure–activity relationship between intrinsic exciton behavior and photocatalytic performance. Comprehensive experimental and theoretical analyses demonstrate that the spatially twisted framework of pBPY-COF induces pronounced exciton effects, promoting energy-mediated singlet oxygen generation. This pathway competes with the oxygen reduction reaction, thereby constraining the H2O2 production efficiency. In contrast, the planar-serrated structure of oBPY-COF enables ultrafast exciton dissociation, facilitating the efficient cooperative utilization of the compounds O2 and H2O for H2O2 synthesis. Remarkably, oBPY-COF achieves a production rate of 3637.8 μmol·h–1·g–1, with an apparent quantum yield (AQY) of 10.5% and a solar-to-chemical conversion efficiency (SCC) of 0.59%. By focusing on excited-state energy transfer, this work elucidates the pivotal role of distinct exciton-mediated reaction pathways in facilitating photocatalytic H2O2 synthesis.