Lignin C–C bond cleavage induced by consecutive two-photon excitation of a metal-free photocatalyst.

Photocatalytic lignin valorization has caught widespread attention; yet the reaction systems often employ noble metal complexes, hydrogen atom transfer (HAT) agents, and/or sacrificial electron donors/acceptors that do not comply with atom economy or environmental friendliness. Herein, we discovered that N-phenylphenothiazine (PTH) as a metal-free photocatalyst induced the cleavage of the lignin Cα–Cβ bond under ambient conditions free of those additional agents with a high yield and selectivity toward benzoic acid. Transient spectroscopic investigations revealed that the energy-demanding Cα–Cβ bond cleavage was induced by the potent oxidant, 2PTH˙+*, that was derived from consecutive two-photon excitation of PTH. [ABSTRACT FROM AUTHOR]