Heteroatom Structural Engineering of Conjugated Porous Polymers Enhances Photocatalytic Nicotinamide Cofactor Regeneration

Heteroatom structural engineering is conducted on conjugated porous polymers. Two novel donor-π-acceptor type conjugated porous polymers (CPPs) photocatalysts are prepared by simply coupling electron-rich thiophene/furan heterocycles with electron deficient triazine respectively. Compared the CPP without S/O heteroatoms, the resulted faster charge separation of heterocyclic CPPs largely enhance the photocatalytic regeneration of nicotinamide cofactor and the photo-enzyme hydrogenation of 2-cyclohexen-1-one.

Abstract

Photocatalysis is an eco-friendly method to regenerate nicotinamide (NADH) cofactors, which is essential for biotransformation over oxidoreductases. Organic polymers exhibit high stability, biocompatibility and functional designability as photocatalysts, but still suffering from rapid charge recombination. Herewith the heteroatom structural engineering of donor-π-acceptor (D-π-A) conjugated porous polymers were conducted to promote charge transfer and photocatalytic NADH regeneration. The electron delocalization of polymer photocatalysts can be readily tuned by changing the electron density of the donor unit, leading to faster charge separation and better photocatalytic performance. The optimum sulfur-doped polymer exhibits the highest NADH regeneration yield of 47.4 % in 30 min and 94.1 % in 4 h, which can drive the biocatalytic C=C bond reduction of 2-cyclohexen-1-one by ene-reductase, giving the corresponding cyclohexanone yield of 96.7 % in 10 h. Moreover, the oxygen-doped polymer, from biomass derived 2,5-diformylfuran, exhibits comparable photocatalytic activity to the sulfur-doped CPP, suggesting the potential of furan as alternative donor unit to thiophene.

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