Triplet state of 2-nitrothiophen. A laser flash-photolysis study
Triplet state of 2-nitrothiophen. A laser flash-photolysis study
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2-硝基噻吩的三重态。
DOI：
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发表时间：
1982
期刊：
影响因子：
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通讯作者：
T. J. Kemp
中科院分区：
文献类型：
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作者：
L. J. A. Martins;T. J. Kemp
293 K 下，2-硝基噻吩 (NT) 在几种极性和非极性溶剂中的纳秒激光闪光光解 (347.1 nm) 显示出以 545 ± 5 nm 为中心的瞬态吸收，Iμ= 9.8 × 103 dm3 mol–1 cm–1，该吸收被指定为 NT 的最低三重激发态，表示为 3NT。虽然 3NT 的 λmax 不随溶剂极性的变化而变化，但其寿命很大程度上取决于溶剂，在甲苯中 < 20 ns，在乙腈中 < 300 ns。三重态-三重态能量转移实验使三重态能量 ET 确定为 247 ± 2 kJ mol-1。
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NT是一种活性物质，在丙酮和乙腈溶液中，分别从二苯甲醇中夺取一个氢原子，k2=(6.70±1.09)×107dm3mol–1s–1，从1,3,5-三甲氧基苯中夺取一个电子，k2=(5.12±0.16)×109dm3mol–1s–1。在水溶液中，与标准氢电极 (SHE) 相比，3NT 的标准还原电位估计为 2.17 V。观察到的反应性模式表明，极性溶剂中的 π-π* 三重态相对于非极性溶剂中能量较低的 n-π* 三重态更加稳定。
Nanosecond laser flash photolysis (347.1 nm) of 2-nitrothiophen (NT) in several polar and non-polar solvents at 293 K shows a transient absorption centred at 545 ± 5 nm with Iµ= 9.8 × 103 dm3 mol–1 cm–1, which is assigned to the lowest triplet excited state of NT, denoted 3NT. Whilst λmax of 3NT does not shift with change of solvent polarity, its lifetime depends strongly on the solvent, being < 20 ns in toluene and 300 ns in acetonitrile. Triplet–triplet energy transfer experiments enabled the triplet energy, ET, to be determined as 247 ± 2 kJ mol–1.
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NT is a reactive species, abstracting a hydrogen atom from diphenylmethanol with k2=(6.70 ± 1.09)× 107 dm3 mol–1 s–1 and an electron from 1,3,5-trimethoxybenzene with k2=(5.12 ± 0.16)× 109 dm3 mol–1 s–1, in acetone and acetonitrile solution, respectively. The standard reduction potential of 3NT is estimated to be 2.17 V vs. the standard hydrogen electrode (SHE), in aqueous solution. The observed pattern of reactivity suggests an increasing stabilisation of a π–π* triplet state in polar solvents relative to a n–π* triplet state, which is considered to be of lower energy in non-polar solvents.