Mikhailova Tatyana V, Mikhailova Valentina A, Ivanov Anatoly I
Volgograd State University, University Avenue 100, Volgograd 400062, Russia.
J Chem Phys. 2024 Oct 21;161(15). doi: 10.1063/5.0237870.
In excited centrosymmetric donor-acceptor triads of type A-D-A or D-A-D, symmetry breaking charge transfer (SBCT) in polar media has been explored for a few decades. SBCT is accompanied by significant reorganization of the electronic structure of the molecule, which leads to a change in the fluorescence transition dipole moment (TDM). Previously, experiments revealed a 20%-30% reduction in TDM, which occurs on the timescale of SBCT. Simple SBCT models explain this reduction. Here, the effect of the interaction of a locally excited state with zwitterionic states on TDM is investigated. This interaction is shown to have a drastic impact on the TDM and its dependence on the solvent polarity. The magnitude of TDM can decrease monotonically, increase monotonically, and also pass through a maximum with an increase in the SBCT degree due to the locally excited state effect. The scale of changes in TDM in the course of SBCT increases greatly. The conditions for the implementation of a particular scenario have been determined. This work clearly demonstrates the observable influence of upper excited states on the photochemistry and photophysics of molecules. Methods for controlling the fluorescent characteristics of quadrupolar molecules are proposed.
在A-D-A或D-A-D型激发中心对称供体-受体三联体中，极性介质中的对称破缺电荷转移（SBCT）已被研究了几十年。SBCT伴随着分子电子结构的显著重组，这导致荧光跃迁偶极矩（TDM）发生变化。此前，实验揭示了TDM在SBCT时间尺度上会降低20%-30%。简单的SBCT模型解释了这种降低现象。在此，研究了局域激发态与两性离子态相互作用对TDM的影响。结果表明，这种相互作用对TDM及其对溶剂极性的依赖性有巨大影响。由于局域激发态效应，TDM的大小可能会单调减小、单调增加，也可能随着SBCT程度的增加而经过一个最大值。在SBCT过程中TDM的变化幅度大幅增加。已确定了实现特定情况的条件。这项工作清楚地证明了上激发态对分子光化学和光物理的可观测影响。提出了控制四极分子荧光特性的方法。
