Donor–Acceptor Pairs in Covalent Organic Frameworks Promoting Electron Transfer for Metal-Free Photocatalytic Organic Synthesis

The donor–acceptor-type covalent organic frameworks (COFs) have recently gained increasing interest in photocatalysis, but the photoinduced electron-transfer regimes in the COFs are underexplored. Herein, we demonstrate a designed porphyrinic COF possessing a donor–acceptor structure together with its photocatalytic performance in aerobic coupling of primary amines. The COF could be photoexcited by the full range of visible light to generate electron–hole pairs that could be separated by donor–acceptor pairs. Electron transfer as the mechanism of the reaction from anthracene unit to porphyrin unit was revealed by natural transition orbitals analyses. The electrons migrate to the adsorbed O2 to generate reactive oxidative species. The COF displays remarkable photocatalytic activities in the coupling of amines to imines, which can be explained mainly by the sufficient charge separation and mobility, benefiting from the donor–acceptor pairs in the COF and their interactions to the reactants and intermediates.