Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
J Chem Phys. 2013 Feb 21;138(7):074304. doi: 10.1063/1.4790595.
The results of a theoretical investigation of coherent π-electron dynamics for nonplanar (P)-2,2'-biphenol induced by ultrashort linearly polarized UV pulses are presented. Expressions for the time-dependent coherent angular momentum and ring current are derived by using the density matrix method. The time dependence of these coherences is determined by the off-diagonal density matrix element, which can be obtained by solving the coupled equations of motion of the electronic-state density matrix. Dephasing effects on coherent angular momentum and ring current are taken into account within the Markov approximation. The magnitudes of the electronic angular momentum and current are expressed as the sum of expectation values of the corresponding operators in the two phenol rings (L and R rings). Here, L (R) denotes the phenol ring in the left (right)-hand side of (P)-2,2'-biphenol. We define the bond current between the nearest neighbor carbon atoms Ci and Cj as an electric current through a half plane perpendicular to the Ci-Cj bond. The bond current can be expressed in terms of the inter-atomic bond current. The inter-atomic bond current (bond current) depends on the position of the half plane on the bond and has the maximum value at the center. The coherent ring current in each ring is defined by averaging over the bond currents. Since (P)-2,2'-biphenol is nonplanar, the resultant angular momentum is not one-dimensional. Simulations of the time-dependent coherent angular momentum and ring current of (P)-2,2'-biphenol excited by ultrashort linearly polarized UV pulses are carried out using the molecular parameters obtained by the time-dependent density functional theory (TD-DFT) method. Oscillatory behaviors in the time-dependent angular momentum (ring current), which can be called angular momentum (ring current) quantum beats, are classified by the symmetry of the coherent state, symmetric or antisymmetric. The bond current of the bridge bond linking the L and R rings is zero for the symmetric coherent state, while it is nonzero for the antisymmetric coherent state. The magnitudes of ring current and ring current-induced magnetic field are also evaluated, and their possibility as a control parameter in ultrafast switching devices is discussed. The present results give a detailed description of the theoretical treatment reported in our previous paper [H. Mineo, M. Yamaki, Y. Teranish, M. Hayashi, S. H. Lin, and Y. Fujimura, J. Am. Chem. Soc. 134, 14279 (2012)].
本文提出了一种理论研究非平面（P）-2,2'-联苯酚在超短线偏振紫外脉冲作用下的相干π电子动力学的方法。通过密度矩阵方法推导出了随时间变化的相干角动量和环电流的表达式。这些相干的时间依赖性由非对角密度矩阵元素决定，该元素可以通过求解电子态密度矩阵的耦合运动方程来获得。在马尔可夫近似下考虑了退相干对相干角动量和环电流的影响。电子角动量和电流的大小表示为两个苯酚环（L 环和 R 环）中相应算符的期望值之和。这里，L（R）表示（P）-2,2'-联苯酚的左侧（右侧）苯酚环。我们将最近邻碳原子 Ci 和 Cj 之间的键电流定义为垂直于 Ci-Cj 键的半平面中的电流。键电流可以表示为原子间键电流。原子间键电流（键电流）取决于半平面在键上的位置，并且在中心处具有最大值。每个环中的相干环电流通过对键电流进行平均来定义。由于（P）-2,2'-联苯酚是非平面的，所以所得的角动量不是一维的。使用通过时间相关密度泛函理论（TD-DFT）方法获得的分子参数，对超短线偏振紫外脉冲激发的（P）-2,2'-联苯酚的随时间变化的相干角动量和环电流进行了模拟。通过相干态的对称性，将随时间变化的角动量（环电流）的振荡行为分类为对称或反对称。对于对称相干态，连接 L 和 R 环的桥键的键电流为零，而对于反对称相干态，键电流不为零。还评估了环电流和环电流感应磁场的大小，并讨论了它们作为超快开关器件中控制参数的可能性。本研究结果详细描述了我们之前的论文[H. Mineo, M. Yamaki, Y. Teranish, M. Hayashi, S. H. Lin, and Y. Fujimura, J. Am. Chem. Soc. 134, 14279 (2012)]中报道的理论处理方法。
