title: Water-assisted self-photoredox of 3-(hydroxymethyl)benzophenone: an unusual photochemistry reaction in aqueous solution.
abstract: An unusual photochemistry of water-assisted self-photoredox of 3-(hydroxymethyl) benzophenone 1 has been investigated by CASPT2//CASSCF computations. The water-assisted self-photoredox is found to proceed via three sequential reactions: an excited-state intermolecular proton transfer (ESIPT), a photoinduced deprotonation, and a self-redox reaction. Upon photoexcitation at 243 nm, the system of 1 is taken to the Franck-Condon region of a short-distance charge transfer (SCT) state of S(SCT)((1)ππ*) and then undergoes ESIPT with a small barrier of ∼3.4 kcal/mol producing the intermediate 2. Subsequently, the singlet-triplet crossing (STC) of STC ((1)ππ*/(3)ππ*) relays 2 by intersystem crossing to the T(SCT)((3)ππ*) state followed by a deprotonation reaction overcoming a moderate barrier of ∼8.0 kcal/mol and finally produces the triplet biradical intermediate 3. Another moderate barrier (∼5.8 kcal/mol) in the T(SCT)((3)ππ*) state has to be overcome so as to relax to a second singlet-triplet crossing STC(T/S0) that allows an efficient spin-forbidden decay to the ground state. The self-redox reaction aided by water molecules occurs with tiny barriers in the S0 state via two steps, protonation of the benzhydrol carbon to produce intermediate 4 and then deprotonation from the benzylic oxygen to yield the final product 3-formylbenzhydrol 5.
authors.affiliation: Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, Department of Chemistry, Beijing Normal University, Xin-wai-da-jie No. 19, Beijing 100875, People's Republic of China. xuebochen@bnu.edu.cn
authors.forename: Xuebo
authors.initials: X
authors.lastname: Chen
authors.forename: Qiangqiang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Yanchang
authors.initials: Y
authors.lastname: Xu
authors.forename: Weihai
authors.initials: W
authors.lastname: Fang
authors.forename: David Lee
authors.initials: DL
authors.lastname: Phillips
mesh_terms: D001577:Benzophenones / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D011789:Quantum Theory; D012996:Solutions; D014867:Water / Q000737:chemistry*
chemical_list: C585002:3-(hydroxymethyl)benzophenone; D001577:Benzophenones; D012996:Solutions; D014867:Water