title: Triplet formation of 4-thiothymidine and its photosensitization to oxygen studied by time-resolved thermal lensing technique.
abstract: Excited-state dynamics of 4-thiothymidine (S4-TdR) and its photosensitization to molecular oxygen in solution with UVA irradiation were investigated. Absorption and emission spectra measurements revealed that UVA photolysis of S4-TdR gives rise to a population of T1(pipi*), following S2(pipi*) --> S1(npi*) internal conversion. In transient absorption measurement, the 355 nm laser photolysis gave broad absorption (380-600 nm) bands of triplet S4-TdR. The time-resolved thermal lensing (TRTL) signal of S4-TdR containing the thermal component due to decay of triplet S4-TdR was clearly observed by the 355 nm laser excitation. The quantum yield for S1 --> T1 intersystem crossing was estimated to be unity by a triplet quenching experiment with potassium iodide. In the presence of molecular oxygen, the photosensitization from triplet S4-TdR gave rise to singlet oxygen O2 (1Deltag) with a quantum yield of 0.50. Therapeutic implications of such singlet oxygen formation are discussed.
authors: Department of Chemistry and Materials Science, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan.
authors: Yosuke
authors: Y
authors: Harada
authors: Tadashi
authors: T
authors: Suzuki
authors: Teijiro
authors: T
authors: Ichimura
authors: Yao-Zhong
authors: YZ
authors: Xu
mesh_terms: D006358:Hot Temperature; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D010777:Photochemistry; D013936:Thymidine / Q000031:analogs & derivatives* / Q000737:chemistry; D013997:Time Factors
chemical_list: C414668:4-thiothymidine; D010100:Oxygen; D013936:Thymidine