Triethanolamine-activated imine-linked covalent organic frameworks for highly efficient NADH generation

Abstract

Conjugated covalent organic frameworks (COFs) integrating different aromatic building units into extended π-conjugated backbones through imine linkages exhibit great potential in photocatalysis but suffer from lower efficiency of intramolecular electron transfer. Herein, we present a new strategy for the reversible activation of imine-linked COFs by triethanolamine (TEOA) under light irradiation. The activated COFs exhibit expanded solar light absorption, elevated reduction potential, decreased chemical impedance, suppressed recombination of charges, and significantly enhanced photocatalytic performance in the generation of nicotinamide adenine dinucleotide (NADH) without any metal cocatalysts. Experimental and theoretical results indicate that the fascinating photocatalytic performance originates from the protonation of imine bonds in the COFs, in which TEOA provides protons in addition to electrons, while light irradiation provides the driving force to overcome the energy barriers. This breaks through the traditional views that imine bonds can only be protonated under acidic conditions and provides new perspectives for the design of metal-free photocatalysts for highly efficient energy conversion.