Volgograd State University, University Avenue 100, Volgograd 400062, Russia.
J Chem Phys. 2023 Apr 28;158(16). doi: 10.1063/5.0147328.
A three-level model of symmetry-breaking charge transfer (SBCT) in excited octupolar molecules is developed. The model describes the joint dynamics of the solvent and the dye in the excited state. For this, a distribution function in the space of two reaction coordinates is introduced. An evolution equation of this function is derived. A strict definition of the reaction coordinates is given, and its dynamic characteristics are determined. The free energy surface in the space of these coordinates is calculated. To quantify the symmetry-breaking degree, a two-dimensional dissymmetry vector is introduced. The model predicts the absence of SBCT in apolar solvents and an abrupt increase in its degree to half the maximum value in weakly polar solvents. The dye dipole moment is revealed to be directed along a molecular arm independently of the direction and the strength of the electric field of the solvent created by its orientational polarization. The conditions for the occurrence and nature of this effect are discussed. The effect of the degeneracy of excited states, which is inherent in octupolar dyes in the excited state, on SBCT is revealed. Degeneracy of energy levels is shown to lead to a significant increase in the symmetry-breaking degree. The effect of SBCT on the dependence of the Stokes on the solvent polarity is calculated and compared with the available experimental data.
建立了激发态八极分子中对称破缺电荷转移 (SBCT) 的三级模型。该模型描述了溶剂和染料在激发态的联合动力学。为此，引入了两个反应坐标空间中的分布函数。推导出该函数的演化方程。严格定义了反应坐标，并确定了其动态特征。计算了这些坐标空间中的自由能表面。为了量化对称破缺程度，引入了二维不对称向量。该模型预测在非极性溶剂中不存在 SBCT，并且在弱极性溶剂中其程度急剧增加到最大值的一半。揭示了染料偶极矩沿分子臂指向，与由其取向极化产生的溶剂电场的方向和强度无关。讨论了发生这种效应的条件和性质。揭示了激发态八极染料中固有的激发态态简并对 SBCT 的影响。能级简并被证明会导致对称破缺程度的显著增加。计算了 SBCT 对斯托克斯依赖于溶剂极性的影响，并将其与现有实验数据进行了比较。
