Light-Driven Depolymerization of Native Lignin Enabled by Proton- Coupled Electron Transfer

Here we report a catalytic, light-driven method for the redox-neutral depolymerization of native lignin biomass at ambient temperature. This transformation proceeds via a proton-coupled electron-transfer (PCET) activation of an alcohol O–H bond to generate a key alkoxy radical intermediate, which then drives the β-scission of a vicinal C–C bond. Notably, this depolymerization is driven solely by visible light irradiation, requiring no stoichiometric chemical reagents and producing no stoichiometric waste. This method exhibits good efficiency and excellent selectivity for the activation and fragmentation of β-O-4 linkages in the polymer backbone, even in the presence of numerous other PCET-active functional groups. DFT analysis suggests that the key C–C bond cleavage reactions produce non-equilibrium product distributions, driven by excited-state redox events. These results provide further evidence that visible-light photocatalysis can serve as a viable method for the direct conversion of lignin biomass into valuable arene feedstocks.