Bifunctional Metal–Organic Layer for Selective Photocatalytic Carbon Dioxide Reduction to Carbon Monoxide

We report a bifunctional metal–organic layer (MOL) as a photocatalyst for CO₂ reduction to CO under visible light irradiation with a turnover number of 6990 in 24 h and a CO selectivity of 99%. The fully accessible and modifiable Hf₁₂ secondary building units and the coordinating porphyrin linkers of the MOL allow for the integration of both Ru photosensitizers and catalytic Fe-porphyrin sites into one single platform. The close distance (∼11 Å) between the Ru photosensitizer and the catalytic center leads to enhanced electron transfer and promotes photocatalytic CO₂ reduction. This strategy leads to an increase of the CO₂-to-CO turnover number for the bifunctional MOL catalyst over a combination of a homogeneous Ru photosensitizer and an Fe-porphyrin complex. The mechanism of MOL-catalyzed CO₂ photoreduction was also studied by photophysical and electrochemical experiments.