Lignin-degrading-inspired dehydrogenative photocatalysis via reductive quenching of donor-acceptor covalent organic framework

Abstract

Achieving a photocatalytic reductive quenching cycle that enables direct oxidation of the photocatalyst radical anion by H(I) species, without requiring stoichiometric oxidants or cocatalysts, remains a long-standing challenge in artificial photoredox catalysis. Here we report a bioinspired approach based on the lignin-degrading-mediated proton-coupled electron transfer (PCET) process, implemented through a perylene-based covalent organic framework (NPy-Per-COF) with precisely engineered donor-acceptor characteristics. This heterogeneous photocatalyst sustains a reductive quenching cycle in which controlled radical generation, catalyst regeneration and hydrogen evolution are intrinsically coupled. The system enables dehydrogenative radical cascade reactions between lignin-inspired precursors and structurally diverse unsaturated partners, providing access to a broad range of functionalized aromatic architectures. Further synthetic modifications and in silico analyses confirm the biological relevance and medicinal potential of the synthesized scaffolds. Beyond model substrates, the photocatalytic system can be extended to lignin-derived motifs, highlighting its potential relevance to complex biomass-related chemical space. Mechanistic investigations support the view that donor-acceptor polarization within the COF promotes efficient charge separation, stabilizes the photocatalyst radical anion and facilitates a PCET-initiated reductive quenching cycle. By abstracting and translating key elements of enzymatic redox control into a fully artificial, heterogeneous photocatalytic framework, this work establishes mechanistically informed design guideline for photocatalytic reductive quenching cycle and advances the development of bioinspired systems for controlled dehydrogenative transformations.