Covalent Organic Frameworks with Tunable Bridge Positions for Photocatalytic CO₂ Reduction to Propylene Under Visible Light Illumination

The use of sunlight to convert CO₂ into multi-carbon fuels, particularly propylene, is considered a sustainable carbon cycle pathway, but propylene requires a multi-electron-coupled proton reaction process that has not been reported. Herein, two covalent organic frameworks (DA-COF and DP-COF) are prepared by varying the bridging positions of anthraquinone conjugated units. The experimental results show that the neighbouring bridge in DA-COF forms a unique cleavage structure like an enzyme catalyst, which can provide an efficient microenvironment for the reduction reaction to trap protons. At the same time, the neighbor bridging in DA-COF can form an electron donor-electron acceptor structure to accelerate the photogenerated carrier migration. As a result, DA-COF exhibits excellent visible light propylene production with a yield of 270.54 µmol g^-1 and no C₃H₆ product is detected by the DP-COF during the reduction process. This study presents a novel avenue for the production of high value-added multi-carbon products using photocatalysis.