Isomerization of Covalent Organic Frameworks for Efficiently Activating Molecular Oxygen and Promoting Hydrogen Peroxide Photosynthesis

Constitutional-isomerized covalent organic frameworks (COFs), constructed by swapping monomers around imine bonds, have attracted attention for their distinct optoelectronic properties, which significantly impact photocatalytic performance. However, limited research has delved into the inherent relationship between isomerization and the enhancement of H₂O₂ photosynthesis. Herein, a pair of isomeric COFs linked by imine bonds (PB-PT-COF and PT-PB-COF) is synthesized, and it is proved that isomeric COFs exhibit different rate-determining steps in the generation process of H₂O₂, resulting in a twofold increase in photocatalytic efficiency. Specifically, PT-PB-COF demonstrates effective adsorption and activation of molecular oxygen (O₂ + e^- → •O₂ ^- + e^- → H₂O₂), leading to a significant improvement in H₂O₂ photocatalytic efficiency. In contrast, PB-PT-COF exhibits robust interaction with H₂O, enabling direct oxidation of H₂O (H₂O + h⁺ → H₂O₂). This study provides a thorough understanding of the intrinsic mechanism underlying the constitutional-isomerized COFs in the photocatalytic H₂O₂ generation, offering insights for further optimizing building units.