Smart Covalent Organic Framework with Proton-Initiated Switchable Photocatalytic Aerobic Oxidation

To conveniently regulate photocatalytic reactions, the design and development of smart photocatalysts, which can realize a series of controllable regulation of their structure, physicochemical properties, photocatalytic activity, and selectivity by simple external stimuli, such as chemical substances, pH, light, electric field, and heat, has aroused keen interest. However, the relevant research is still in its infancy. Herein, a smart imine covalent-organic-framework (COF) photocatalyst HP-n (n represents the pH of COF pretreatment, n = 1∼7) with proton-initiated switchable photocatalytic aerobic oxidation has been prepared. In the structure, the imine units can be reversibly protonated, which leads to the COF skeleton rearrangement from the phenolic to its quinone structure. The corresponding absorption band edge is expanded from 463 nm (HP-7) to 630 nm (HP-1). Meanwhile, the excitation energy transfer, oxygen adsorption, and activation change significantly, endowing HP-n with smartly switchable 1O2 production and interesting proton-initiated efficiency photocatalytic sulfide oxidation with both conversion and sulfoxide selectivity >99%. This work demonstrates a smart imine-COF photocatalyst, which paves the way for the development of smart photocatalysts and reveals the critical roles of protons in the structure–property–activity relationship of COF photocatalysts.