Zhao Guang-Jiu, Han Ke-Li, Lei Yi-Bo, Dou Yu-Sheng
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China.
J Chem Phys. 2007 Sep 7;127(9):094307. doi: 10.1063/1.2768347.
Detailed simulation study is reported for the excited-state dynamics of photoisomerization of cis-tetraphenylethylene (TPE) following excitation by a femtosecond laser pulse. The technique for this investigation is semiclassical dynamics simulation, which is described briefly in the paper. Upon photoexcitation by a femtosecond laser pulse, the stretching motion of the ethylenic bond of TPE is initially excited, leading to a significant lengthening of ethylenic bond in 300 fs. Twisting motion about the ethylenic bond is activated by the energy released from the relaxation of the stretching mode. The 90 degrees twisting about the ethylenic bond from an approximately planar geometry to nearly a perpendicular conformation in the electronically excited state is completed in 600 fs. The torsional dynamics of phenyl rings which is temporally lagging behind occurs at about 5 ps. Finally, the twisted TPE reverts to the initial conformation along the twisting coordinate through nonadiabatic transitions. The simulation results provide a basis for understanding several spectroscopic observations at molecular levels, including ultrafast dynamic Stokes shift, multicomponent fluorescence, viscosity dependence of the fluorescence lifetime, and radiationless decay from electronically excited state to the ground state along the isomerization coordinate.
报道了飞秒激光脉冲激发后顺式四苯乙烯（TPE）光异构化激发态动力学的详细模拟研究。本研究采用的技术是半经典动力学模拟，本文对此进行了简要描述。在飞秒激光脉冲光激发下，TPE烯键的拉伸运动首先被激发，导致烯键在300飞秒内显著伸长。烯键的扭转运动由拉伸模式弛豫释放的能量激活。在电子激发态下，烯键从近似平面几何结构扭转90度至接近垂直构象的过程在600飞秒内完成。苯基环的扭转动力学在时间上滞后，约在5皮秒时发生。最后，扭曲的TPE通过非绝热跃迁沿扭转坐标恢复到初始构象。模拟结果为在分子水平上理解若干光谱观测提供了基础，包括超快动态斯托克斯位移、多组分荧光、荧光寿命的粘度依赖性以及沿异构化坐标从电子激发态到基态的无辐射衰变。
