title: Observation of singlet cycloreversion of thymine oxetanes by direct photolysis.
abstract: An ultrafast broadband transient absorption spectroscopic study of the direct photolysis of oxetane DMT-BP [which is the oxetane adduct of 1,3-dimethylthymine (DMT) with benzophenone (BP)] is presented. Previous nanosecond time-resolved absorption studies by other researchers observed that direct photolysis of such oxetanes results in a rare, adiabatic photochemical reaction to produce a triplet excited-state carbonyl species. However, the mechanism for this adiabatic photochemical reaction remained unclear for the reaction sequence of the bond scission and the intersystem crossing (ISC) because of the time resolution for the experiments, and this prompted us to further study its mechanism with ultrafast time-resolution. The ultrafast time-resolved spectra presented here indicate that the cycloreversion reaction occurs in a stepwise manner on a singlet excited-state, and then intersystem crossing (ISC) occurs to produce the triplet carbonyl product observed in the previously reported nanosecond time-resolved experiments.
authors: Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, PR China.
authors: Wai Ming
authors: WM
authors: Kwok
authors: Xiangguo
authors: X
authors: Guan
authors: Lai Man
authors: LM
authors: Chu
authors: Wenjian
authors: W
authors: Tang
authors: David Lee
authors: DL
authors: Phillips
mesh_terms: D000042:Absorption; D001577:Benzophenones / Q000737:chemistry / Q000528:radiation effects*; D004988:Ethers, Cyclic / Q000737:chemistry / Q000528:radiation effects*; D005609:Free Radicals; D008956:Models, Chemical; D013057:Spectrum Analysis; D013941:Thymine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects*; D013997:Time Factors
chemical_list: D001577:Benzophenones; D004988:Ethers, Cyclic; D005609:Free Radicals; C039199:N,N-dimethylthymine; C047723:benzophenone; C005287:oxetane; D013941:Thymine