Excited state properties of 5‐fluoro‐4‐thiouridine derivative^†

Sato, Rin; Yamada, Yoshino; Kashihara, Wataru; Nishihara, Tatsuya; Tanabe, Kazuhito; Xu, Yao-Zhong and Suzuki, Tadashi (2024). Excited state properties of 5‐fluoro‐4‐thiouridine derivative^†. Photochemistry and Photobiology (Early Access).

DOI: https://doi.org/10.1111/php.13918

Abstract

The excited state properties of thionated 5- fluorouridine (2′,3′,5′- tri- O- acetyl- 5- fluoro- 4- thiouridine; ta5F4TUrd), synthesized with Lawesson's reagent, have been intensively investigated with nanosecond transient absorption spectroscopy, time- resolved thermal lensing, near- infrared emission, and quantum chemical calculation. The intrinsic triplet lifetime of ta5F4TUrd was determined to be 4.2±0.7μs in acetonitrile, and the formation quantum yield of the excited tri-plet state was as large as 0.79±0.01. The quenching rate constants of the triplet ta5F4TUrd by the dissolved oxygen molecule and by the self- quenching process were found to be nearly equal to the diffusion- controlled rate of acetonitrile. The quantum yield of the singlet molecular oxygen produced through energy transfer between the triplet ta5F4TUrd and the dissolved oxygen, Φ_Δ, was successfully de-termined to be 0.61±0.02 under the oxygen- saturated condition. From the oxy-gen concentration dependence of the Φ_Δ value, the fraction of triplet ta5F4TUrd quenched by dissolved oxygen which gives rise to the ¹O₂* formation, S_Δ, was successfully obtained to be 0.78±0.01, which was the largest among the thionu-cleobases and the thionucleosides reported so far. This could be due to the lower energy and/or the ππ* character of the triplet state.

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