Donor–Acceptor Pairs in Covalent Organic Frameworks\nPromoting Electron Transfer for Metal-Free Photocatalytic Organic\nSynthesis

Abstract

The\ndonor–acceptor-type covalent organic frameworks (COFs)\nhave recently gained increasing interest in photocatalysis, but the\nphotoinduced electron-transfer regimes in the COFs are underexplored.\nHerein, we demonstrate a designed porphyrinic COF possessing a donor–acceptor\nstructure together with its photocatalytic performance in aerobic\ncoupling of primary amines. The COF could be photoexcited by the full\nrange of visible light to generate electron–hole pairs that\ncould be separated by donor–acceptor pairs. Electron transfer\nas the mechanism of the reaction from anthracene unit to porphyrin\nunit was revealed by natural transition orbitals analyses. The electrons\nmigrate to the adsorbed O₂ to generate reactive oxidative\nspecies. The COF displays remarkable photocatalytic activities in\nthe coupling of amines to imines, which can be explained mainly by\nthe sufficient charge separation and mobility, benefiting from the\ndonor–acceptor pairs in the COF and their interactions to the\nreactants and intermediates.