Functional group substitution strongly influences the performances of covalent organic frameworks in the photocatalytic metal-free oxidase reaction

Abstract

The exceptional performance of covalent organic frameworks (COFs) serving as metal-free photocatalysts has been demonstrated in numerous oxidation reactions. However, the intricate structure–activity relationship between the components, structures and reactivity of COFs remains poorly understood. This is due to their photocatalytic activity being influenced by various factors, including light absorption, charge carrier generation, separation, transport, and surface adsorption. In this study, a series of COFs with different functional group substitutions but similar topological structures were employed to investigate the relationship between the molecular structure and catalytic activity. The results reveal an activity trend in the representative superoxide radical-mediated Aza–Henry reaction, with COF-Br > COF-Cl > COF-H > COF-OMe > COF-H. Both the experimental results and density functional theory calculations confirm that the catalytic activities of COFs are closely linked to the band gap and electron affinity of the initial monomers. This study of the relationship offers a rational, time- and energy-saving strategy for developing effective COF-based photocatalysts. This approach involves evaluating the physical properties of COF monomers rather than conducting catalytic screenings on final solid COFs.