The insertion of thiazolo[5,4-d]thiazole unit in covalent triazine framework for boosting the photocatalytic capacities in both selective aerobic oxidation of sulfides and amines

Abstract

Recently, covalent triazine frameworks (CTFs) have realized versatile applications in the field of photocatalysis. Herein, two CTFs photocatalysts were designed and synthesized with or without thiazolo[5,4-d]thiazole (TzTz), an electron deficient unit, to highlight the introduction of an additional acceptor unit on the photocatalytic aerobic oxidation reaction of triazine based CTFs. Specifically, CTF-TZDA was prepared by a condensation reaction between terephthalimidamide and 4,4′-(thiazolo[5,4-d]thiazole-2,5-diyl) dibenzaldehyde (TzTz aldehyde), and similarly, CTF-FPBA was prepared between terephthalimidamide and [1,1′-biphenyl]-4,4′-dicarbaldehyde. CTF-TZDA showed high photocatalytic activities towards aerobic oxidation of both benzyl sulfides and benzyl amines to benzyl sulfoxides and benzyl imines, respectively, and the reaction was powered by blue light. A wide range of substrates can be aerobically oxidized with high yield (about 99%) and high selectivity over CTF-TZDA photocatalyst. The insertion of the TzTz unit lowered that band gap, accelerated the delocalization of π electrons, and elevated the LUMO levels of CTF-TZDA, which are beneficial to extend the light absorption range, and to promote the separation and transfer of photo-induced charge carriers. This work indicates that the insertion of an additional electron deficient unit rich in heteroatoms is considered as a feasible approach towards enhancing the photocatalytic activity of CTFs.