Engineering the linkage of mesoporous covalent organic frameworks for enhancing selective photocatalytic oxidation of organic sulfides

Abstract

The modular architecture and inherent porosity of covalent organic frameworks (COFs) form the basis for their photocatalytic applications. Herein, the condensation of 1,3,5-tris(4-formylphenyl)triazine (TFPT) with linkers [1,1′:4,1″-terphenyl]-4,4″-diacetonitrile (TCN) and [1,1′:4′,1″-terphenyl]-4,4″-diamine (TDA), respectively, affords two COFs, TFPT-sp²c-TCN and TFPT–TDA. In both COFs, the sufficiently long TCN and TDA linkers create mesopores that facilitate the mass transfer of organic molecules. Combined theoretical and experimental results confirm that TFPT-sp²c-TCN, with a cyano-vinylene linkage, exhibits enhanced optoelectronic properties, including extended conjugation and improved charge dynamics, compared to TFPT–TDA with an imine linkage. TFPT-sp²c-TCN demonstrates high and stable photocatalytic conversion of organic sulfides to sulfoxides via two reactive oxygen species, superoxide and singlet oxygen, over four catalytic cycles. In sharp contrast, TFPT–TDA shows negligible activity. This work underlines that engineering the linkage of COFs is viable for enhancing photocatalytic activity.