Merging benzotrithiophene covalent organic framework photocatalysis with TEMPO for selective oxidation of organic sulfides

Visible light photocatalysis of covalent organic frameworks(COFs) has made significant progress in recent years. Benzotrithiophene(BTT), a planar, electron-rich building block, turns out to be foundational in assembling COFs in which the fullπ-conjugation of BTT is essential to facilitate electron transfer. Herein, a sp~2 carbon-conjugated COF, namely BTT-sp~2c-COF, is assembled from benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde and [1,1′:4′,1′′-terphenyl]-4,4′′-dicarbonitrile towards photocatalysis. More importantly, TEMPO(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 1 mol%) could considerably accelerate the selective oxidation of organic sulfides with O_(2) over BTT-sp~2c-COF. TEMPO mediates hole transfer between BTT-sp~2c-COF and organic sulfides, and O-atoms are incorporated into sulfoxides via an electron transfer pathway. Merging BTT-sp~2c-COF photocatalysis with TEMPO generally applies to transforming organic sulfides into sulfoxides. This work implies the full π-conjugation of electron-rich building blocks into COFs is a viable strategy for selective visible light photocatalysis.