Photoisomerization of Silyl-Substituted Cyclobutadiene Induced by sigma -> pi Excitation: A Computational Study
Photoisomerization of Silyl-Substituted Cyclobutadiene Induced by sigma -> pi Excitation: A Computational Study
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sigma -> pi 激发诱导甲硅烷基取代的环丁二烯的光异构化：一项计算研究
DOI：
10.1021/jp503220q
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发表时间：
2015
影响因子：
2.9
通讯作者：
Liu Chungen
中科院分区：
文献类型：
--
作者：
Qu Zexing;Yang Chen;Liu Chungen
利用完全主动空间自一致场（CASSCF）方法，研究了四（三甲基硅基）-环丁二烯（TMS-CBD）在frank - condon （FC）激发下的光致化学过程，探索了几个低洼激发态之间的势能表面交叉。利用单激励和双激励运动方程耦合簇模型（EOM-CCSD）和多参考Møller-Plesset （MRMP）方法计算了垂直激励能。在发现计算结果与实验观测之间的极好吻合后，我们提出Franck-Condon激发态不对应于第一个π -π *单激发态（S1, 11b1），而对应于第二个1b1态（S3），其特征为σ -π *单激发态。从Franck-Condon区开始，沿一个异构化通道和一个解离通道有一系列的锥形交叉点（CIs）。通过异构化通道，TMS-CBD转化为四（三甲基硅基）-四面体烷（TMS-THD），这一异构化过程可能通过“四”形锥形交叉发生。另一方面，通过进一步拉伸较长的C-C键产生两个双（三甲基硅基）-乙炔（TMS-Ac）分子的解离通道在激发到tos3态后可能比异构化通道更具竞争性。这一机制图景与最近报道的实验观察结果非常吻合。
Photoinduced chemical processes upon Franck–Condon (FC) excitation in tetrakis(trimethylsilyl)-cyclobutadiene (TMS-CBD) have been investigated through the exploration of potential energy surface crossings among several low-lying excited states using the complete active space self-consistent field (CASSCF) method. Vertical excitation energies are also computed with the equation-of-motion coupled-cluster model with single and double excitations (EOM-CCSD) as well as the multireference Møller–Plesset (MRMP) methods. Upon finding an excellent coincidence between the computational results and experimental observations, it is suggested that the Franck–Condon excited state does not correspond to the first π–π* single excitation state (S1, 11B1state in terms ofD2symmetry), but to the second1B1state (S3), which is characterized as a σ–π* single excitation state. Starting from the Franck–Condon region, a series of conical intersections (CIs) are located along one isomerization channel and one dissociation channel. Through the isomerization channel, TMS-CBD is transformed to tetrakis(trimethylsilyl)-tetrahedrane (TMS-THD), and this isomerization process could take place by passing through a “tetra form” conical intersection. On the other hand, the dissociation channel yielding two bis(trimethylsilyl)-acetylene (TMS-Ac) molecules through further stretching of the longer C–C bonds might be more competitive than the isomerization channel after excitation intoS3state. This mechanistic picture is in good agreement with recently reported experimental observations.