Transient UV pump-IR probe investigation of heterocyclic ring-opening dynamics in the solution phase: the role played by nσ* states in the photoinduced reactions of thiophenone and furanone.
Transient UV pump-IR probe investigation of heterocyclic ring-opening dynamics in the solution phase: the role played by nσ* states in the photoinduced reactions of thiophenone and furanone.
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DOI：
10.1039/c4cp03653k
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发表时间：
2014-09
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通讯作者：
D. Murdock;S. J. Harris;Joel Luke;M. Grubb;A. Orr-Ewing;M. Ashfold
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作者：
D. Murdock;S. J. Harris;Joel Luke;M. Grubb;A. Orr-Ewing;M. Ashfold
通过超快瞬态红外光谱研究了溶解在 CH3CN 中的噻吩酮和呋喃酮的杂环开环动力学。在 267 nm（噻吩酮）或 225 nm（呋喃酮）照射后，通过在 2150 cm(-1) 附近出现特征性反对称乙烯酮拉伸特征，证实了快速 (τ < 1 ps) 开环。开环产物分子在高度振动激发下形成，随后在~6.7 ps 的时间尺度上冷却。通过监测母体 (S0) 漂白剂的回收率，发现约 60% 的初始光激发噻吩酮分子重新形成母体分子，这与呋喃酮的情况形成鲜明对比，其中母体漂白剂回收率低于 10%。沿 S-C([双键，长度为中划线]O) 和 O-C([双键，长度为中划线]O) 开环坐标的势能从头计算互补，揭示了对反应机理的见解，以及解离 (n/π)σ* 态在此类杂环系统的 UV 诱导光化学中所起的重要作用。
The heterocyclic ring-opening dynamics of thiophenone and furanone dissolved in CH3CN have been probed by ultrafast transient infrared spectroscopy. Following irradiation at 267 nm (thiophenone) or 225 nm (furanone), prompt (τ < 1 ps) ring-opening is confirmed by the appearance of a characteristic antisymmetric ketene stretching feature around 2150 cm(-1). The ring-opened product molecules are formed highly vibrationally excited, and cool subsequently on a ∼6.7 ps timescale. By monitoring the recovery of the parent (S0) bleach, it is found that ∼60% of the initially photoexcited thiophenone molecules reform the parent molecule, in stark contrast with the case in furanone where there is less than 10% parent bleach recovery. Complementary ab initio calculations of potential energy cuts along the S-C([double bond, length as m-dash]O) and O-C([double bond, length as m-dash]O) ring-opening coordinate reveals insights into the reaction mechanism, and the important role played by dissociative (n/π)σ* states in the UV-induced photochemistry of such heterocyclic systems.