The effect of excitation pulse carrier frequency on ultrafast charge recombination dynamics of excited donor–acceptor complexes

Abstract

The excitation of a charge transfer band by a laser pulse of finite duration and the ensuing charge recombination are calculated in the framework of the perturbation theory. The influence of the spectral characteristics of the laser pulse on the charge recombination dynamics is investigated for models including several nuclear modes that differ greatly in their timescales. It is shown that, in the area of applicability of the perturbation theory, the variation of the pulse carrier frequency inside the absorption band can significantly change the effective charge recombination rate constant.

Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

“…Of course, because of the Franck-Condon principle, an equilibrated ion pair population for which CR is in the normal regime cannot be optically prepared upon CT excitation. Theoretical calculations performed by Ivanov and co-workers, using both the time-dependent perturbation theory and the stochastic point transition approach predict that, with the exception of very weakly exergonic processes ( G CR > −0.4 eV), the CR dynamics should slow down with decreasing excitation wavelength [111][112][113]. To confirm this prediction, we have undertaken an experimental investigation of the effect of excitation wavelength on various DACs in polar solvents [114,115].…”

Effect of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of donor-acceptor complexes: Stochastic simulations and experiments

“…This is supported by the results obtained within the framework of nonstationary perturbation theory. 20 For this reason, and also to clear up the mechanism of the spectral effect caused by the solvent, a model which does not include intramolecular high-frequency vibrations is investigated in this paper. Nevertheless, the quantitative description of the spectral effect may require these vibrations to be accounted for and such a research is planned in the near future.…”

“…The dependence of the spectral effect on the electronic coupling obtained within the framework of the nonequilibrium Golden Rule for the model with two Debye modes 20 is presented in Fig. 6͑b͒.…”

“…The influence of nonequilibrium and especially coherent vibrational motion on electronic transitions has received considerable attention in theoretical studies of both time-dependent fluorescence [5][6][7][8][9][10][11] and electron transfer ͑ET͒ reactions. [12][13][14][15][16][17][18][19][20] The coherent underdamped motion on the reactant free energy surface results in a variety of subtle effects on the reaction dynamics. 17,18,21,22 In this case, every visit of the wave packet in the term crossing region ͑TCR͒ has to lead to a stepwise decrease of the reactant state population.…”

Influence of spectral characteristics of the pump pulse on the transient absorption of donor–acceptor complexes in polar solvents

“…In slowly relaxing solvents, the effective CR rate constant proved to depend on the pump-pulse time. The phenomenon was given the name spectral effect [19]. For all three DACs, the influence of a solvent on the signal dynamics proved to be of one type, whereas the spectral effect depends substantially on the DAC nature.…”