Rh-Functionalized\nDonor−π–Acceptor\nCovalent Organic Framework for Efficient Photocatalytic Nicotinamide\nCofactor Regeneration

A nicotinamide\nadenine dinucleotide phosphate (NADPH)-mediated\nphotoenzyme-coupled catalytic system is an attractive and green strategy\nfor chemical conversion. However, artificial photocatalytic NADPH\nregeneration with low activity and selectivity has posed a challenge\nwhen it is coupled with enzyme catalysis. Therefore, we developed\na strategy to prepare an “all-in-one” photocatalyst\n(Rh-sp<sup>2</sup>c-COF) by immobilizing an electron mediator ([Cp*Rh(bpy)(H<sub>2</sub>O)]<sup>2+</sup>) in a covalent organic framework (COF) with\na donor−π–acceptor structure for efficient photocatalytic\nNADPH regeneration. The immobilized [Cp*Rh(bpy)(H<sub>2</sub>O)]<sup>2+</sup> not only achieves specific regeneration of 1,4-NADPH but\nalso improves the efficiency of electron transfer and utilization\nby constructing intramolecular electron transfer channels and electron\nbuffer tanks. In addition, the donor−π–acceptor\nstructure expands the range of light absorption and promotes effective\ncarrier separation and directional transfer. The turnover frequency\nof NADPH regeneration by Rh-sp<sup>2</sup>c-COF reaches 2.17 mmol·g<sub>COF</sub><sup>–1</sup>·h<sup>–1</sup>, which is\n3.28, 1.99, and 4.5 times higher than those of sp<sup>2</sup>c-COF,\nsp<sup>2</sup>c-COF + free [Cp*Rh(bpy)(H<sub>2</sub>O)]<sup>2+</sup>, and imine-COF, respectively. Finally, Rh-sp<sup>2</sup>c-COF coupled\nwith ene reductase achieves efficient asymmetric hydrogenation of\nCC. This work provides an approach for accurate predesign\nof photocatalysts to achieve efficient conversion and utilization\nof solar energy.