Thermal isomerization of azobenzenes: on the performance of Eyring transition state theory
Thermal isomerization of azobenzenes: on the performance of Eyring transition state theory
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偶氮苯的热异构化：Eyring 过渡态理论的表现
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
P. Saalfrank
中科院分区：
文献类型：
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作者：
Clemens Rietze;E. Titov;S. Lindner;P. Saalfrank
偶氮苯的热Z→E（反）异构化反应是分子开关中的典型反应。它已经被研究了几十年，但其动力学尚未完全了解。在本文中，量子化学计算进行模拟的实验基准系统，其中改性偶氮苯（AzoBiPyB）嵌入在金属有机框架（MOF）的动力学。该分子可以在无溶剂条件下从顺式热转换为反式。我们严格测试Eyring过渡态理论对该反应的有效性。正如以前发现的其他偶氮苯（虽然在溶液中），理论和实验之间的良好协议出现的活化能和活化自由能，已经在一个比较简单的理论水平，B3 LYP/6- 31 G * 包括色散校正。然而，理论上的Arabius前因子和激活熵与实验在定性上不一致。几个因素进行了讨论，可能有影响的激活熵，其中动态和几何约束（施加的MOF）。对于偶氮苯的Z →E异构化这一较简单的模型，在Eyring理论的框架下，对密度泛函理论和波函数理论的量子化学方法进行了系统的检验.此外，非谐性对激活熵的影响进行了讨论。我们的工作突出了Eyring过渡态理论和量子化学方法在无溶剂条件下应用于偶氮苯的Z→E（反）异构化反应时的能力和缺点。
The thermal Z→E (back-)isomerization of azobenzenes is a prototypical reaction occurring in molecular switches. It has been studied for decades, yet its kinetics is not fully understood. In this paper, quantum chemical calculations are performed to model the kinetics of an experimental benchmark system, where a modified azobenzene (AzoBiPyB) is embedded in a metal-organic framework (MOF). The molecule can be switched thermally from cis to trans, under solvent-free conditions. We critically test the validity of Eyring transition state theory for this reaction. As previously found for other azobenzenes (albeit in solution), good agreement between theory and experiment emerges for activation energies and activation free energies, already at a comparatively simple level of theory, B3LYP/6-31G* including dispersion corrections. However, theoretical Arrhenius prefactors and activation entropies are in qualitiative disagreement with experiment. Several factors are discussed that may have an influence on activation entropies, among them dynamical and geometric constraints (imposed by the MOF). For a simpler model—Z→E isomerization in azobenzene—a systematic test of quantum chemical methods from both density functional theory and wavefunction theory is carried out in the context of Eyring theory. Also, the effect of anharmonicities on activation entropies is discussed for this model system. Our work highlights capabilities and shortcomings of Eyring transition state theory and quantum chemical methods, when applied for the Z→E (back-)isomerization of azobenzenes under solvent-free conditions.