Designing conjugated microporous polymers for visible light-promoted photocatalytic carbon-carbon double bond cleavage in aqueous medium

The production of valuable carbonyl compounds directly from alkenes via carbon-carbon double (C=C) bond cleavage is a highly important reaction. As a promising alternative to traditional metal-catalyzed thermal reaction conditions, photocatalysis offers an environmentally friendly and sustainable synthetic strategy. However, most photocatalysts used so far were homogeneous, molecular and transition metal-based catalytic systems. Here, we report a structural design strategy of conjugated microporous polymers (CMPs) as a class of metal-free, heterogeneous, stable and reusable photocatalysts for visible light-promoted C=C bond cleavage reaction. Via different electron donor and acceptor combinations in the CMP backbone structure, we systematically investigated the structural influence of the CMPs on their optical and electrochemical properties, thereby revealing the structure and performance relationship in the photocatalytic C=C bond cleavage reaction. As a result, the CMP with a specific electron donor-acceptor combination containing benzothiazole as a strong electron withdrawing unit and phenyl as a weak electron donating unit was the most efficient photocatalyst. The C=C bond in various alkenes, mostly styrene derivatives, could be successfully cleaved, forming aldehydes as a product with high conversion and moderate to high selectivity. The green aspect of the work is demonstrated by the utilization of visible-light, molecular oxygen as a cheap oxidant and water-based reaction medium.