Benzotrithiophene conjugated microporous polymer photocatalysts for selective aerobic sulfoxidation driven by green light

Abstract

Porous organic materials with conjugated skeletons, highly delocalized π–π conjugations, and stable chemical bonds have excellent potential as visible light photocatalysts. Essentially, the efficiency depends on the building blocks, among which the electron-rich and planar benzotrithiophene is highly favored. Here, starting with benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde (BTT), 1,4-phenylenediacetonitrile (PDAN) and 1,4-phenylenediamine (PDA) building blocks are adopted to synthesize two porous organic materials linked with vinylene and imine, respectively. The less reversible vinylene only allows the formation of a conjugated microporous polymer (CMP), BTT-PDAN-CMP. In contrast, the more reversible imine enables the construction of a covalent organic framework (COF), BTT-PDA-COF. Despite being amorphous, BTT-PDAN-CMP displays better optoelectronic properties than BTT-PDA-COF due to enhancing electron transfer by vinylene. BTT-PDAN-CMP turns out to to be an efficient photocatalyst. Substantially, BTT-DPAN-CMP, as a visible light photocatalyst, demonstrates better efficiency than BTT-PDA-COF for selective aerobic sulfoxidation. Driven by green light over BTT-PDAN-CMP, molecular oxygen is transformed to superoxide and singlet oxygen that contribute to the highly selective formation of organic sulfoxides. This work underlines the importance of rational design for porous organic materials as visible light photocatalysts.