人工分子马达的理论研究——偶氮苯的光致异构化机制与承力能力

【作者】 邵俊峰；

【导师】 王志松；

【作者基本信息】 复旦大学 ， 原子与分子物理， 2009， 硕士

【摘要】 生物马达如kinesin和dynein表明直到分子层次仍然存在功能很强的轨道定向行走。这些生物马达在生物细胞内承担着运输各种物质的重要作用。我们课题组提出了利用激光控制的光化学分子机车能够在易于实现的轨道上定向行走。该分子机车的核心机制是周期性的功循环,即周期性的将激光提供的能量转化为机械功,然后经过调制成连续的,定向的运动。偶氮苯是构造分子机车骨架的主要候选分子,而且广泛应用其他纳米器件。本论文模拟研究偶氮苯分子的光-力转化过程,及其抗阻力能力。重点探讨使用该分子作为分子纳米马达骨架的可能性。本论文对偶氮苯分子光致异构化过程进行了非绝热模拟研究。本文采用半经典的电子-辐射-核动力学方法(semiclassical electron-radiation-ionmethod),该方法描述含时情况下分子结构和电子动力学的耦合演化。模拟计算的结果表明,在没有外力条件下偶氮苯异构化为平面外绕轴转动的运动。在外阻力条件下该运动模式没有本质改变。我们系统地扫瞄了激光的各个参数,没有发现之前有人提出的平面内翻转机制。模拟计算表明90-200pN大小的力能够阻碍光致异构化。在无激光条件下,计算还表明1250-1650pN的拉力可能导致纯力学的异构化过程.力学异构化包含相当程度的平面内反转,但最终通过转动实现。最后,我们讨论本文发现对于含偶氮苯纳米器件/马达的意义。更多还原

【Abstract】 Biomotors such as kinesin and dynein show us that robust track-walking is possible down to molecular scale. Our group designed a laser-powered molecular locomotive that is able to do that on an easily constructed track. The core of the machine is its work cycle that periodically converts optical energy into mechanical work, which is further rectified into processive, directional motion. Azobenzene molecule is a major candidate for the backbone of the molecular locomotive. It is also widely used in other mechanical nanodevices. This thesis investigates theoretically the optomechanical conversion capacity of azobenzene molecule.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-to-trans state if the azobenzene molecule is stretched by an external force of about 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 nanomotors and nanodevices are discussed.更多还原