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首页> 外文期刊>Chemistry: A European journal >Pseudo-bimolecular [2+2] cycloaddition studied by time-resolved photoelectron spectroscopy
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Pseudo-bimolecular [2+2] cycloaddition studied by time-resolved photoelectron spectroscopy

机译：用时间分辨光电子能谱研究伪双分子[2 + 2]环加成反应

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The first study of pseudo-bimolecular cycloaddition reaction dynamics in the gas phase is presented. We used femtosecond time-resolved photoelectron spectroscopy (TRPES) to study the [2+2] photocycloaddition in the model system pseudo-gem-divinyl[2.2]paracyclophane. From X-ray crystal diffraction measurements we found that the ground-state molecule can exist in two conformers; a reactive one in which the vinyl groups are immediately situated for [2+2] cycloaddition and a nonreactive conformer in which they point in opposite directions. From the measured S_1 lifetimes we assigned a clear relation between the conformation and the excited-state reactivity; the reactive conformer has a lifetime of 13 ps, populating the ground state through a conical intersection leading to [2+2] cycloaddition, whereas the nonreactive conformer has a lifetime of 400 ps. Ab initio calculations were performed to locate the relevant conical intersection (CI) and calculate an excited-state [2+2] cycloaddition reaction path. The interpretation of the results is supported by experimental results on the similar but nonreactive pseudo-para-divinyl[2.2]paracyclophane, which has a lifetime of more than 500 ps in the S_1 state.
机译：提出了气相中拟双分子环加成反应动力学的第一项研究。我们使用飞秒时间分辨光电子能谱（TRPES）来研究模型系统伪-gem-divinyl [2.2]对环环烷中的[2 + 2]光环加成。通过X射线晶体衍射测量，我们发现基态分子可以存在于两个构象异构体中。一种反应性基团，其中乙烯基可立即位于[2 + 2]环加成反应中;一种非反应性构象异构体，其指向相反的方向。根据测得的S_1寿命，我们在构象和激发态反应性之间分配了明确的关系。反应性构象异构体的寿命为13 ps，通过圆锥相交填充基态，导致[2 + 2]环加成，而非反应性构象异构体的寿命为400 ps。从头算开始进行计算以找到相关的圆锥交点（CI），并计算激发态[2 + 2]环加成反应路径。对结果的解释得到了类似但不反应的伪对-二乙烯基[2.2]对环环烷类的实验结果的支持，在S_1状态下其寿命超过500 ps。

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