Department of Physics, Volgograd State University, University Avenue 100, Volgograd 400062, Russia.
J Phys Chem A. 2010 Dec 23;114(50):12998-3004. doi: 10.1021/jp1072796. Epub 2010 Nov 23.
The charge recombination dynamics of excited donor-acceptor complexes in polar solvents has been investigated within the framework of the stochastic approach. The model involves the excited state formation by the pump pulse and accounts for the reorganization of a number of intramolecular high-frequency vibrational modes, for their relaxation as well as for the solvent reorganization following nonexponential relaxation. The hot transitions accelerate the charge recombination in the low exergonic region and suppress it in the region of moderate exothermicity. This straightens the dependence of the logarithm of the charge recombination rate constant on the free energy gap to the form that can be fitted to the experimental data. The free energy dependence of the charge recombination rate constant can be well fitted to the multichannel stochastic model if the donor-acceptor complexes are separated into a few groups with different values of the electronic coupling. The model provides correct description of the nonexponential charge recombination dynamics in excited donor-acceptor complexes, in particular, nearly exponential recombination in perylene-tetracyanoethylene complex in acetonitrile. It appears that majority of the initially excited donor-acceptor complexes recombines 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 in the area of the low and moderate exothermicity.
在随机方法的框架内，研究了极性溶剂中激发给体-受体复合物的电荷复合动力学。该模型通过泵浦脉冲来激发激发态，并考虑了许多分子内高频振动模式的重组，以及它们的弛豫以及非指数弛豫后的溶剂重组。热跃迁加速了低放能区域的电荷复合，抑制了中等放热区域的电荷复合。这使得电荷复合速率常数的对数对自由能间隙的依赖性呈直线形式，可以拟合实验数据。如果将给体-受体复合物分为具有不同电子耦合值的几个组，则电荷复合速率常数的自由能依赖性可以很好地拟合多通道随机模型。该模型为激发给体-受体复合物的非指数电荷复合动力学提供了正确的描述，特别是在乙腈中的苝-四氰乙烯复合物中几乎呈指数的复合。当非平衡波包通过对应于电子基态振动激发态的跃迁的多个项交叉时，最初激发的给体-受体复合物中的大多数在非热（热）阶段中复合，在低和中等放热区域。
