Imine-linked 2D covalent organic frameworks based on benzotrithiophene for visible-light-driven selective aerobic sulfoxidation

Abstract

Recently, emerging visible-light photocatalysts such as covalent organic frameworks (COFs) have undergone rapid development due to the molecular tunability and structural diversity. Imine takes an overriding role in reversible covalent bonds to form COFs, which usually lack high activity because the polarity of imine hampers light-driven electron transfer. In principle, this barrier can be overcome by exploring the electron push–pull effect of the molecular building units. In this work, with benzotrithiophene as the electron donor, two imine-linked 2D (two-dimensional) COFs were successfully synthesized by the condensation of BTT (benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde) with TAPT (2,4,6-tris(4-aminophenyl)-1,3,5-triazine) and TAPB (1,3,5-tris(4-aminophenyl)benzene), giving BTT-TAPT-COF and BTT-TAPB-COF, respectively. The density functional theory calculation predicted that BTT-TAPT-COF with an electron-withdrawing triazine core can boost charge separation, and the superiority was further verified by optoelectronic properties. Both imine-linked 2D COFs based on benzotrithiophene can activate dioxygen, in which BTT-TAPT-COF exhibits better activity based on the prominent properties. BTT-TAPT-COF was found to be a photocatalyst for blue-light-driven selective aerobic sulfoxidation with outstanding versatility and reusability. This work paints a clear picture of how the electron push–pull effect of the building units of COFs regulates the ensuing activity in visible-light photocatalysis.