Built-in Electric Field in Multivariate COFs Boosts Photocatalytic NADH Regeneration for Enzymatic Reduction

Solar-driven in situ nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] regeneration provides a sustainable route for producing high-value chemicals using NAD(P)H-dependent reductases. However, its efficiency is frequently restricted by the low charge separation efficiency of photocatalysts. To address this limitation, we developed a series of built-in electric field multivariate covalent organic framework (MTV-COF) photocatalysts with donor-acceptor-acceptor (D-A-A) structures to enhance the charge separation. The resultant MTV-COFs with a 0.06 wt % immobilized Rh cocatalyst achieved a NADH regeneration rate of 763.5 mol·mol_Rh^-1·h^-1 with 95.7% regioselectivity, surpassing the performance of most reported photocatalysts. This is ascribed to the significantly enhanced separation and transfer efficiency of photogenerated electrons and minimized steric hindrance within the COF pores. Furthermore, coupling this highly efficient NADH-regenerating photocatalyst with enzymatic reduction reactions enabled continuous l-glutamic acid and (S)-2-phenylpropanol production, reaching total NADH regeneration turnover numbers of 80 and 71, respectively, which are significantly higher than previously reported values. This work underscores the critical importance of the D-A-A structural motif design in MTV-COF-Rh to generate a built-in electric field to enhance the charge separation for efficient photocatalysis.