Enhanced Performance of Metal- and Additive-Free Pyridinium-Based Photocatalysts for Selective Aerobic Oxidation: The Role of Anion Exchange in Boosting Reactive Oxygen Species Generation

Developing economically and environmentally sustainable protocols for highly effective and selective oxidation of organics is of crucial importance in both academia and industry. Aiming at activating molecular oxygen to form reactive oxygen species as the key oxidant, a series of pyridinium-based small molecules have been designed and developed as simple and effective photocatalysts for the aerobic oxidation of alcohols to aldehydes. A facile anion exchange strategy is applied to introduce heavy atoms, which promote the generation of singlet oxygen and reduce the competitive effect between electron donors. A remarkably improved photocatalytic selectivity is realized in a simple, effective, and green approach at room temperature in an air atmosphere without any metals or additives. In the face of increasingly serious energy and environmental issues, this work provides new insights into molecular oxygen activation and reveals the great potential of the pyridinium family as a green and sustainable catalyst system toward an advanced oxidation reaction and the utilization of light energy.