Verification of Nonequilibrium Mechanism of Ultrafast Charge Recombination in Excited Donor–Acceptor Complexes

Mikhailova, T. V.; Михайлова, В. А.; Ivanov, Anatoly I.

doi:10.1021/acs.jpcb.7b02537

Cited by 14 publications

(11 citation statements)

References 60 publications

(131 reference statements)

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“…For the numerical solution of eq , the Brownian simulation method is used, which operates in terms of stochastic trajectories and was successfully used for simulation of electron transfer kinetics. ,− A set of the stochastic trajectories describe the motion of an ensemble of particles on the free energy surface G ( D m ). The free energy G ( D m ) is numerically found by minimization of the free energy functional G int [Ψ, P⃗ ( r⃗ )] with respect to the dissymmetry parameter D using the golden-section search, so far as the domain of the variable D is restricted and belongs the range −1 ≤ D ≤ 1 as well as the G int [Ψ, P⃗ ( r⃗ )] has only one minimum in this domain for a given value of D m .…”

Section: Theoretical Methodsmentioning

confidence: 99%

Nonstationary Theory of Excited State Charge Transfer Symmetry Breaking Driven by Polar Solvent

Nazarov

Ivanov

2020

J. Phys. Chem. B

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A consistent theory of electron transfer symmetry breaking (SB) dynamics in excited quadrupolar molecules in polar solvents is developed. The interaction of the electronic subsystem of the molecule with intramolecular degrees of freedom and solvent polarization is taken into account and is divided into interaction with inertial and inertialess degrees of freedom. A strong influence of the inertialess polarization of the solvent on the extent of symmetry breaking is revealed. The theory is nonlinear due to the equilibration of inertialess degrees of freedom to the solute electronic state. The interaction of a molecule with the inertial solvent polarization is described in terms of a single variablethe reaction coordinate, for which a rigorous definition is given. The free energy of the system is derived, and the motion of the system along the reaction coordinate is modeled by the Smoluchowski equation. The theory is adapted to describe the dynamics of SB in real solvents characterized by several relaxation time scales. Conditions for the applicability of a much simpler stationary SB model are formulated. The role of thermal fluctuations in the solvent polarization is clarified. Instead of the magnitude of the dissymmetry parameter, a distribution function of molecules over this parameter is introduced. An analysis of the Franck–Condon state created by a short pump pulse shows that it has distinct features of a state with broken symmetry for a wide range of parameters. Thermal fluctuations of the solvent polarization are shown to crucially affect SB.

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Section: Theoretical Methodsmentioning

confidence: 99%

Nonstationary Theory of Excited State Charge Transfer Symmetry Breaking Driven by Polar Solvent

Nazarov

Ivanov

2020

J. Phys. Chem. B

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“…Nonequilibrium ultrafast charge recombination also proceeds to form the products in excited vibrational states. 31 Typically, the decay of excited vibrational states is extremely fast due to intramolecular vibrational redistribution and relaxation. 50 Influence of the product state decay on the probability of nonequilibrium ET was investigated in refs 51 and 52.…”

Section: ■ Theory and Computational Detailsmentioning

confidence: 99%

“…31 The effects of the excitation pulse carrier frequency and the solvent viscosity on ultrafast charge recombination in DACs were rather well described in the framework of the stochastic multichannel point-transition model. 22,31 The intramolecular high-frequency mode excitation by a pumping pulse also can affect the ultrafast ET kinetics. Recently, a great deal of experimental evidence on the influence of high-frequency intramolecular vibration excitation on the ET dynamics has been obtained.…”

Section: ■ Introductionmentioning

confidence: 99%

“…22−24 It has recently been shown that the dynamic solvent effect observed in the region of strong exergonicity for ultrafast charge recombination in excited DACs 35 is even more convincing proof that the reaction proceeds in nonequilibrium regime. 31 The effects of the excitation pulse carrier frequency and the solvent viscosity on ultrafast charge recombination in DACs were rather well described in the framework of the stochastic multichannel point-transition model. 22,31 The intramolecular high-frequency mode excitation by a pumping pulse also can affect the ultrafast ET kinetics.…”

Section: ■ Introductionmentioning

confidence: 99%

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Effect of Reactant and Product State Decay on Ultrafast Charge-Transfer Kinetics: Violation of the Principle of Independence of Elementary Chemical Reactions

Михайлова

Ivanov

2017

J. Phys. Chem. C

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Fast decay of both the reactant and product states is shown to strongly increase the intrinsic electron transfer rate in donor−acceptor dyads. The decay is associated with redistribution/ relaxation of excited vibrational states that typically participate in the reaction. Although the role of the reorganization of high-frequency vibrational modes in electron-transfer dynamics is well understood and it is commonly accepted to strongly affect the ultrafast electron transfer dynamics, the influence of the relaxation of excited vibrational states on electron transfer is not accounted for in experimental data analysis. In photoinduced electron transfer, excited states of high-frequency vibrational modes are often produced by laser pump pulse so that the ultrafast charge separation, at least partly, occurs from excited vibrational states. The charge recombination accompanying the charge separation also essentially occurs from excited vibrational states of intermediates to form a final excited vibrational state. Since the decay of the reactant state and electron transfer are two elementary chemical reactions occurring in parallel, the influence of vibrational relaxation on the intrinsic electron-transfer rate constant is a clear manifestation of the violation of the fundamental principle of chemical kinetics postulating the independence of elementary chemical reactions. The mechanism of the violation is discussed in detail. The transition probability that better characterizes the efficiency of ultrafast nonequilibrium charge recombination than the rate constant is calculated. The dependencies of the electron-transfer rate constant and the transition probability on the product decay time are predicted to be identical while on the reactant decay time to be opposite.

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“…The theories describing proton/electron transfer in terms of the thermal rate constant are applicable for the description of the reactions which are significantly slower than the vibrational and solvent relaxations. Ultrafast reactions proceed on timescale of nuclear relaxation and nonequilibrium of the solvent and intramolecular vibrational modes can be of paramount importance. − Thus, theoretical treatment of ultrafast reactions has to include nonequilibrium of the nuclear subsystem formed by an excitation pulse and specific stages of a complex reaction. Ultrafast stages of the reactions proceed in parallel with the relaxation of the nonequilibrium state created at the previous stage, and hence, the memory about it is preserved.…”

Section: Introductionmentioning

confidence: 99%

Modeling Kinetics of Ultrafast Photoinduced Intramolecular Proton-Coupled Electron Transfer

2018

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A model of photoinduced intramolecular proton-coupled electron transfer is derived. The model includes three states as follows: the ground, excited, and product states. The charge transfer is associated with both stages, photoexcitation and product formation. A larger part of the model parameters can be extracted from the stationary absorption and fluorescence spectra of a particular fluorophore. Two different reaction coordinates are associated with the two stages, which are not independent. The angle between the reaction coordinates strongly influences on the kinetics of ultrafast product formation. The stochastic multichannel approach is exploited for simulations of the kinetics. The simulations well reproduce the kinetics of ultrafast intramolecular protoncoupled electron transfer in 2-((2-(2-hydroxyphenyl)benzo[d]oxazol-6-yl)methylene)malononitrile in a few solvents. The transfer is shown to occur totally or partly, depending on the solvent, in the nonequilibrium regime. Analysis of the kinetics of the excited-state decay has uncovered a significant decrease in the magnitude of the reorganization energies of slow nuclear modes with increasing the solvent polarity. Such an unusual behavior of the total reorganization energy can be rationalized under the assumptions: (i) a slow intramolecular reorganization of a significant magnitude associates with the transition between excited and product states and (ii) intramolecular slow reorganization is accompanied by a change in the dipole moment of the fluorophore.

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Verification of Nonequilibrium Mechanism of Ultrafast Charge Recombination in Excited Donor–Acceptor Complexes

Cited by 14 publications

References 60 publications

Nonstationary Theory of Excited State Charge Transfer Symmetry Breaking Driven by Polar Solvent

Nonstationary Theory of Excited State Charge Transfer Symmetry Breaking Driven by Polar Solvent

Effect of Reactant and Product State Decay on Ultrafast Charge-Transfer Kinetics: Violation of the Principle of Independence of Elementary Chemical Reactions

Modeling Kinetics of Ultrafast Photoinduced Intramolecular Proton-Coupled Electron Transfer

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