Light-driven site-selective O–H activation in lignin by triplet excited alkylanthraquinone at simulated natural conditions

Harnessing photocatalyzed hydrogen atom transfer (HAT) for the precise activation of C–H/O–H bonds is a pivotal yet challenging strategy to selectively drive oxidative C–C bond scission in renewable lignin, yielding value-added chemicals with exceptional selectivity. Herein, we present a metal-free photochemical strategy that enables selective C–C bond scission in lignin via a unique synergistic HAT pathway driven by triplet-excited 2-ethylanthraquinone (EAQ*) and hydroxyl radicals ( • OH) generated in situ from EAQH 2 and O 2 . Under simulated natural conditions, this process achieves a benzaldehyde yield of 146.6 mol% from a lignin-derived phenolic dimer. Mechanistic investigations reveal that preferential activation of the C α -OH in lignin facilitates a tandem HAT process, forming alkoxy radical intermediates that undergo β –scission to produce benzaldehyde, as corroborated by extensive control reactions and density functional theory calculations. Furthermore, this straightforward protocol efficiently cleaves the C–C bonds of technical kraft lignins, providing a rapid, scalable, and metal-free protocol for lignin valorization under mild conditions.