偶氮苯光异构化反应的非绝热模拟研究：详细机理和抗负荷能力
Nonadiabatic simulation study of photoisomerization of azobenzene: Detailed mechanism and load-resisting capacity
摘要：
采用非绝热动力学模拟方法研究了偶氮苯在激光和机械载荷作用下的顺反异构化反应。我们使用了半经典的电子辐射离子动力学方法，是能够描述的结构动力学和底层的电子动力学的协同演化的实时方式。研究发现，偶氮苯光异构化主要是通过面外旋转机制发生的，即使在几十微微牛顿的非平凡阻力下也是如此。我们已经重复了模拟系统的激光脉冲的参数范围很广，但不能找到任何光致异构化事件由以前提出的面内反转机制。模拟发现，光异构化过程可以通过90 - 200 pN的外部阻力来阻止，这取决于激光的频率和强度。本研究还发现，如果偶氮苯分子被1250 - 1650 pN的外力拉伸，则可能从顺式状态发生纯机械异构化。值得注意的是，机械异构化首先通过机械活化反转进行，然后转向超快下坡旋转，完成异构化。这些研究结果的影响偶氮苯为基础的纳米机械设备进行了讨论。
英文摘要：
Nonadiabatic dynamical simulations were carried out to study cis-to-trans isomerization of azobenzene under laser irradiation and/or external mechanical loads. We used a semiclassical electron-radiation-ion dynamics method that is able to describe the coevolution of the structural dynamics and the underlying electronic dynamics in a real-time manner. It is found that azobenzene photoisomerization occurs predominantly by an out-of-plane rotation mechanism even under a nontrivial resisting force of several tens of piconewtons. We have repeated the simulations systematically for a broad range of parameters for laser pulses, but could not find any photoisomerization event by a previously suggested in-plane inversion mechanism. The simulations found that the photoisomerization process can be held back by an external resisting force of 90 - 200 pN depending on the frequency and intensity of the lasers. This study also found that a pure mechanical isomerization is possible from the cis state if the azobenzene molecule is stretched by an external force of 1250 -1650 pN. Remarkably, the mechanical isomerization first proceeds through a mechanically activated inversion, and then is diverted to an ultrafast downhill rotation that accomplishes the isomerization. Implications of these findings to azobenzene-based nanomechanical devices are discussed.
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