Photocatalytic Properties and Mechanistic Insights into Visible Light-Promoted Aerobic Oxidation of Sulfides to Sulfoxides via Tin Porphyrin-Based Porous Aromatic Frameworks

Using concepts of biomimetic catalysis, a kind of tin porphyrin-based porous aromatic framework (SnPor@ PAF) with broad and strong optical absorption in the visible light region was successfully synthesized and subsequently used in the aerobic oxidation of sulfides to sulfoxides under ambient conditions and visible light irradiation, in which exhibited enzyme-like features of high efficiency and high selectivity. More interestingly, heterogeneous SnPor@PAF was naturally regarded as an intriguing and versatile photosensitizer for photocatalytic transformation and could be reused several times because of its robust and rigid porphyrin framework. As expected, their pi-conjugated structure characteristic in the molecular skeleton might facilitate the activation of molecular oxygen under mild reaction conditions and promoted the production of reactive oxygen species (singlet oxygen (O-1(2)) and superoxide radical anion (O-2(.-))), which would involve energy transfer and/or electron transfer process. Experimental investigations including emission quenching experiment, oxygen-isotope labelling, typical inhibition experiments, classical fluorescence probe study, photo-oxidation of alpha-terpinene and in situ electron spin resonance, could provide a mechanistic insight into the photocatalytic reactions.