Wang Xiaofang, Guo Jirui, Li Tanping, Wei Zhiyi
School of Physics and Optoelectronic Engineering, Xidian University Xi'an 710071 People's Republic of China
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190 China.
RSC Adv. 2020 May 13;10(31):18348-18354. doi: 10.1039/d0ra01227k. eCollection 2020 May 10.
The connections between the non-equilibrium solvation dynamics upon optical transitions and the system's equilibrium fluctuations are explored in aqueous liquid. Linear response theory correlates time-dependent fluorescence with the equilibrium time correlation functions. In the previous work [T. Li, , 2017, , 1867], Stokes shift was explicitly decomposed into the contributions of various order time correlation functions on the excited state surface. Gaussian fluctuations of the solute-solvent interactions validate linear response theory. Correspondingly, the deviation of the Gaussian statistics causes the inefficiency of linear response evaluation. The above mechanism is thoroughly tested in this study. By employing molecular simulations, multiple non-equilibrium processes, not necessarily initiated from the ground state equilibrium minimum, were examined for tryptophan. Both the success and failure of linear response theory are found for this simple system and the mechanism is analyzed. These observations, assisted by the width dynamics, the initial state linear response approach, and the variation of the solvation structures, integrally verify the virtue of the excited state Gaussian statistics on the dynamics of Stokes shift.
在水性液体中探索了光学跃迁时的非平衡溶剂化动力学与系统平衡涨落之间的联系。线性响应理论将随时间变化的荧光与平衡时间关联函数联系起来。在之前的工作中 [T. Li, , 2017, , 1867]，斯托克斯位移被明确分解为激发态表面上各种阶次时间关联函数的贡献。溶质 - 溶剂相互作用的高斯涨落验证了线性响应理论。相应地，高斯统计的偏差导致线性响应评估效率低下。本研究对上述机制进行了全面测试。通过分子模拟，研究了色氨酸的多个非平衡过程，这些过程不一定从基态平衡最小值开始。对于这个简单系统，发现了线性响应理论的成功与失败之处，并对其机制进行了分析。这些观察结果，借助宽度动力学、初始态线性响应方法以及溶剂化结构的变化，整体验证了激发态高斯统计在斯托克斯位移动力学方面的优点。
