Triplet Formation of 4-Thiothymidine and Its Photosensitization to Oxygen Studied by Time-Resolved Thermal Lensing Technique

Harada, Y; Suzuki, T; Ichimura, T and Xu, YZ (2007). Triplet Formation of 4-Thiothymidine and Its Photosensitization to Oxygen Studied by Time-Resolved Thermal Lensing Technique. Journal of Physical Chemistry B, 111(19) pp. 5518–5524.

DOI: https://doi.org/10.1021/jp0678094

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(*), following S2(*) f S1(n*) 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 f 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 (1g) with a quantum yield of 0.50. Therapeutic implications of such singlet oxygen formation are discussed.