A new kind of photochemistry associated with meta-substituted anthraquinone(AQ)was reported,where a novel photoredox reaction reduces the ketone moiety to its alcohol,and the meta-substituted alcohol group is oxidized to its aldehyde(or ketone).However,the precise mechanism for self-photoredox is still unclear.In this work we use multi-configurational perturbation theory at the CASPT2//CASSCF//AMBER QM/MM level to investigate the photoredox reaction of 2-(1-Hydroxyethyl)9,10-Anthraquinone,which is proposed to proceed via three sequential reactions: an excited-state intermolecular proton transfer(ESIPT),the photoinduced deprotonation,and the self-redox.Triggered by photoexcitation,the charge transfer occurs from the aromatic ring of the benzyl alcohol to the carbonyl group,leading to an abundant gathering of negative charge around the center of the carbonyl group that can function as a potential acceptor for a proton transfer and then undergoes ESIPT aided by water molecules.Subsequently,the system relaxes to the 3ππ* state from charge transfer 1ππ* state via an intersystem crossing(ISC)followed by deprotonation reaction from the methylene C-H group.The self-redox reaction is achieved by protonation of another carbonyl group from the proton donor of aqueous solution in the ground state.