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

Covalent organic frameworks (COFs) with photoactive units have attracted significant interest in visible light photocatalysis and can present a metal-free scenario for activating O-2. 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 beta-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 beta-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 O-2. Furthermore, with O-2 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 (O-2(center dot-)) is the crucial reactive oxygen species. This study highlights the superiority of TzTz-embedded COFs in developing effective photocatalytic systems for organic transformations. (C) 2022, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

This study demonstrates the application of TzTz-embedded COFs in photocatalytic organic transformations. By embedding TzTz into the building blocks of COFs, microspherical TpDTz-COFs were formed, which exhibited superior performance in blue light photocatalytic selective oxidation reactions.