Feskov Serguei V, Ionkin Vladimir N, Ivanov Anatoly I, Hagemann Hans, Vauthey Eric
Department of Physics, Volgograd State University, University Avenue 100, Volgograd, Russia.
J Phys Chem A. 2008 Jan 31;112(4):594-601. doi: 10.1021/jp709587x. Epub 2008 Jan 9.
The charge recombination dynamics of excited donor-acceptor complexes consisting of hexamethylbenzene (HMB), pentamethylbenzene (PMB), and isodurene (IDU) as electron donors and tetracyanoethylene (TCNE) as electron acceptor in various polar solvents has been investigated within the framework of the stochastic approach. The model accounts for the reorganization of intramolecular high-frequency vibrational modes as well as for the solvent reorganization. All electron-transfer energetic parameters have been determined from the resonance Raman data and from the analysis of the stationary charge transfer absorption band, while the electronic coupling has been obtained from the fit to the charge recombination dynamics in one solvent. It appears that nearly 100% of the initially excited donor-acceptor complexes recombine in a nonthermal (hot) stage when the nonequilibrium wave packet passes through a number of term crossings corresponding to transitions toward vibrational excited states of the electronic ground state. Once all parameters of the model have been obtained, the influence of the dynamic solvent properties (solvent effect) and of the carrier frequency of the excitation pulse (spectral effect) on the charge recombination dynamics have been explored. The main conclusions are (i) the model provides a globally satisfactory description for the IDU/TCNE complex although it noticeably overestimates the spectral effect, (ii) the solvent effect is quantitatively well described for the PMB/TCNE and HMB/TCNE complexes but the model fails to reproduce their spectral effects, and (iii) the positive spectral effect observed with the HMB/TCNE complex cannot be described within the framework of two-level models and the charge redistribution in the excited complexes should most probably be taken into account.
在随机方法的框架内，研究了由六甲基苯（HMB）、五甲基苯（PMB）和异杜烯（IDU）作为电子供体以及四氰基乙烯（TCNE）作为电子受体组成的激发态供体 - 受体复合物在各种极性溶剂中的电荷复合动力学。该模型考虑了分子内高频振动模式的重组以及溶剂重组。所有电子转移能量参数均从共振拉曼数据和对稳态电荷转移吸收带的分析中确定，而电子耦合则通过拟合一种溶剂中的电荷复合动力学获得。当非平衡波包通过一些对应于向电子基态的振动激发态跃迁的能级交叉时，似乎几乎100%的初始激发供体 - 受体复合物在非热（热）阶段发生复合。一旦获得了模型的所有参数，就探索了动态溶剂性质（溶剂效应）和激发脉冲的载频（光谱效应）对电荷复合动力学的影响。主要结论如下：（i）尽管该模型明显高估了光谱效应，但它对IDU/TCNE复合物提供了总体上令人满意的描述；（ii）对于PMB/TCNE和HMB/TCNE复合物，溶剂效应在定量上得到了很好的描述，但该模型未能再现它们的光谱效应；（iii）在HMB/TCNE复合物中观察到的正光谱效应无法在双能级模型的框架内描述，并且很可能应考虑激发复合物中的电荷重新分布。
