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- -> center dot 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. Combined with theoretical calculations and experimental results, it is proved that different rate determining steps are exhibited in the H2O2 generation process for a pair of isomeric COFs (PB-PT-COF and PT-PB-COF). PB-PT-COF shows strong interaction with H2O, facilitating the direct oxidation of H2O, while PT-PB-COF exhibited effective adsorption and activation of molecular oxygen, resulting in a 2-fold enhancement in the H2O2 photosynthesis. image