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

Abstract

The influence of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of excited donor-acceptor complexes has been explored both theoretically and experimentally. The theoretical description involves the explicit treatment of both the optical formation of the nuclear wave packet on the excited free energy surface and its ensuing dynamics. The wave packet motion and the electronic transition are described within the framework of the stochastic point-transition approach. It is shown that the variation of the pulse carrier frequency within the absorption band can significantly change the effective charge recombination dynamics. The mechanism of this phenomenon is analyzed and a semiquantitative interpretation is suggested. The role of the vibrational coherence in the recombination dynamics is discussed. An experimental investigation of the ultrafast charge recombination dynamics of two donor-acceptor complexes in valeronitrile also is presented. The decays of the excited state population were found to be highly nonexponential, the degree of non-exponentiality depending on the excitation frequency. For one complex, the charge recombination dynamics was found to slow down upon increasing the excitation frequency, while the opposite behavior was observed with the other complex. These experimental observations follow qualitatively the predictions of the simulations.

Solvent and Spectral Effects in the Ultrafast Charge Recombination Dynamics of Excited Donor−Acceptor Complexes

“…This allows us to obtain the following general expression for the initial probability distribution function on the excited term 15 where…”

Charge recombination in excited donor-acceptor complexes with two absorption bands

“…Suppose that the pumping pulse is fairly narrow, and its electric field has the form E(t) = E 0 exp(-iΩ e t -t 2 / ). This assumption allows us to very accurately calculate the initial distribution at the U ej excited term [25], (10) Here,…”

“…The suggested model was tested numerically using Brownian modeling methods developed in [25,26]; 10 5 random trajectories were used in calculations.…”

Remote Electron Transfer in Donor-Acceptor Complexes: the Influence of Photoexcitation Pulse Carrier Frequency

“…Первый из них объясняет спектральный эффект в терминах неравновесных волновых пакетов, образо-ванных на электронном терме состояния с переносом заряда в результате оптической накачки ДАК [5]. В рамках этого подхода различия в кинетике рекомбинации зарядов при возбуждении ДАК на разных частотах связаны с различиями в траекториях движения этих волновых паке-тов вдоль маркусовых поляризационных координат растворителя.…”

“…В рамках этого подхода различия в кинетике рекомбинации зарядов при возбуждении ДАК на разных частотах связаны с различиями в траекториях движения этих волновых паке-тов вдоль маркусовых поляризационных координат растворителя. Численные исследования показывают, что спектральный эффект в этой модели может быть как положительным (уско-рение рекомбинации зарядов при синем смещении несущей частоты импульса накачки), так и отрицательным [5].…”