Thiazolo[5,4-d]thiazole-based covalent organic framework microspheres for blue light photocatalytic selective oxidation of amines with O2

Abstract

Covalent organic frameworks (COFs) with photoactive units have attracted significant interest in visible light photocatalysis and can present a metal-free scenario for activating O2. As a typical photoactive unit, thiazolo[5,4-d]thiazole (TzTz) has rarely been added to COFs. However, circumventing the low reversibility of TzTz, it could be embedded into the building blocks beforehand, along with other bonds like β-ketoenamine in forming COFs. TzTz was embedded into 1,1′-biphenyl-4,4′-diamine (BD) using this approach to produce 4,4′-(TzTz-2,5-diyl)dianiline (DTz). Under organobase-modulated solvothermal conditions, combining 1,3,5-triformylphloroglucinol (Tp) with BD and DTz resulted in the production of β-ketoenamine-linked TpBD-COF and TpDTz-COF. Both TpDTz-COF and TpBD-COF are microspheres. TpDTz-COF possessed more adequate separation and charge migration than TpBD-COF. This resulted in superior performance for the blue light photocatalytic selective oxidation of benzylamine with O2. Furthermore, with O2 as the main oxidant, a wealth of benzylamines could be converted into imines over TpDTz-COF. Mechanistic investigations substantiate that oxidation of benzylamines obeys an electron transfer pathway, in which superoxide anion (O2•–) is the crucial reactive oxygen species. This study highlights the superiority of TzTz-embedded COFs in developing effective photocatalytic systems for organic transformations.