Indolo[3,2-b]carbazole-based hyper-cross-linked polymers for blue-light-driven selective organic sulfide oxidation in water

Abstract

The development of metal-free and water-stable photocatalysts for visible light-induced environmentally friendly organic transformations in water is of great significance in the context of green and sustainable development. In this work, two hyper-cross-linked polymers (HCPs), NUT-19 and NUT-19-Me, were successfully synthesized through the covalent linkage of two cross-linkers containing different groups with indolo[3,2-b]carbazole (ICZ) derivatives. Their pore structures and photochemical properties were characterized. Driven by 420 nm blue light, both exhibited good catalytic activity (NUT-19: 99% conversion in 8 h; NUT-19-Me: 98% conversion in 11 h) and high selectivity (greater than 95% for sulfoxide) for organic sulfide oxidation in water. NUT-19 outperformed NUT-19-Me due to its superior photochemical properties. Extended to other sulfide derivatives, both maintained efficient catalytic activity and selectivity. The photocatalytic performance can be well-maintained over eight cycles in water, indicating good stability. Mechanistic studies revealed that under blue light irradiation, the materials could generate singlet oxygen (¹O₂), which achieved the selective oxidation of sulfides to sulfoxides. This work provides new insights into the development of ICZ-based stable and environmentally friendly photocatalysts and opens up new avenues for their application in green chemical synthesis.