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 μs in acetonitrile, and the formation quantum yield of the excited triplet state was as large as . 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, , was successfully determined to be under the oxygen-saturated condition. From the oxygen concentration dependence of the value, the fraction of triplet ta5F4TUrd quenched by dissolved oxygen which gives rise to the ¹O₂* formation, , was successfully obtained to be , which was the largest among the thionucleobases and the thionucleosides reported so far. This could be due to the lower energy and/or the ππ* character of the triplet state.

中文翻译：

---

5-氟-4-硫尿苷衍生物的激发态特性†

使用 Lawesson 试剂合成的硫代 5-氟尿苷（2',3',5'-三-O-乙酰基-5-氟-4-硫尿苷；ta5F4TUrd）的激发态性质已通过纳秒瞬态吸收光谱进行了深入研究、时间分辨热透镜、近红外发射和量子化学计算。ta5F4TUrd 的固有三重态寿命确定为μs 在乙腈中，激发三重态的形成量子产率为。发现溶解氧分子和自猝灭过程对三重态 ta5F4TUrd 的猝灭速率常数几乎等于乙腈的扩散控制速率。通过三重态 ta5F4TUrd 和溶解氧之间的能量转移产生的单线态分子氧的量子产率，, 被成功判定为在氧饱和条件下。从氧浓度依赖性值，三重态 ta5F4TUrd 被溶解氧猝灭形成¹ O ₂ * 的分数，, 成功获得为，这是迄今为止报道的硫核碱基和硫核苷中最大的。这可能是由于三重态的较低能量和/或 ππ* 特征。