Donor-acceptor 2D covalent organic frameworks for efficient heterogeneous photocatalytic α-oxyamination

Covalent organic frameworks (COFs) have received widespread interest due to their high porosity, excellent crystallinity, tailorable structures, and broad application prospects. It has been demonstrated that proper combination and arrangement of electron donor and acceptor units in 2D conjugated COF lattice could promote efficient charge separation and electron transfer, and thus is beneficial for photocatalysis. In this article, three donor-acceptor (D-A) 2D COFs were prepared by Schiff base reaction of electron acceptor 4,4 ',4 '',4 '''-(benzo[1,2-d:4,5-d ']bis(oxazole)-2,4,6,8-tetrayl)tetraaniline (BBO) with different electron donors: thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT), benzo[1,2-b:4,5-b ']dithiophene-2,6-dicarboxaldehyde (BDT) and terephthalaldehyde (Ph), respectively. These D-A 2D COFs exhibited prominent photocatalytic activity towards alpha-oxyamination of 1,3-dicarbonyl with 2,2,6,6-tetramethyl-1-piperdinyloxy (TEMPO) upon visible light irradiation. Among these D-A(BBO)-COFs, D-TT-A(BBO)-COF exhibited the highest photocatalytic rates, which can be ascribed to the more negative highest occupied molecular orbital (HOMO) and narrower bandgap. The excellent stability, high activity and superior recyclability render D-TT-A(BBO)-COF as a potential and environmentally friendly heterogeneous catalyst for alpha-oxyamination.