Benzobisthiazole covalent organic framework photocatalysis for selective oxidation of benzyl amines†

Abstract

Covalent organic frameworks (COFs) enable highly effective photocatalysis due to their crystallinity, tunable pores and channels, and expansive light absorption. The performance of COFs in photocatalysis is underpinned by the intrinsic tendency of charge separation and transfer, thereby depending on the molecular building blocks. Benzobisthiazole (BBT), with an electron-withdrawing effect, shows superior potential in various optoelectronic materials. Therefore, with tetrabutylammonium hydroxide as a catalyst, a fully conjugated COF, BBT-sp²c-COF, is synthesized from 2,2′-(benzo[1,2-d:4,5-d′]bis(thiazole)-2,6-diyl)diacetonitrile and 1,3,6,8-tetrakis(4-formylphenyl)pyrene. As such, a series of characterizations demonstrate the structural and optical properties of BBT-sp²c-COF. The fully conjugated COF, BBT-sp²c-COF, possesses enhanced charge separation, electron transfer, and recycling stability. As expected, BBT-sp²c-COF photocatalysis achieves effective selective oxidation of benzyl amines with oxygen under blue light irradiation. Superoxide is identified as the crucial reactive oxygen species during the formation of imines. The full conjugation of organic building blocks into COFs can achieve highly effective photocatalysis.