Dynamic Solvent Effects Research Articles

Solvent dynamical effects in electron transfer: electrochemical-exchange kinetics of sesquibicyclic hydrazines as a probe of coupled vibrational activation

Abstract : Rate constants for electrochemical exchange of three sesquibicyclic hydrazine-radical cation redox couples, k(e)(ex), obtained at mercury by means of phase-selective ac voltammetry, are reported in seven solvents - acetonitrile, acetone, nitromethane, N, N-dimethylformamide, dimethylsulfoxide, benzonitrile and methanol. The hydrazine couples - denoted here 1+/0, 2+/0, and 3+/0 - feature variations in the bridgehead alkyl groups; they each exhibit substantial high-frequency vibrational barriers (4.5-5 kcal mol-1) to electrochemical exchange. These system's therefore provide an interesting opportunity for the assessment of the manner and extent in which overdamped solvent relaxation may limit the electron-transfer dynamics under such circumstances. As in previous studies (ref. 2), scrutiny of the solvent- dependent rate constants enable at least semiquantitative estimates of the degree to which the kinetics are controlled by solvent dynamics as well as activation energetics. In addition to the usual dielectric-continuum treatment, estimates of the latter outer-shell component required for the solvent-dynamical analysis were required from an observed SESQUIBICYCLIC HYDRAZINES, ELECTRON- TRANSFER DYNAMICS, ELECTROCHEMICAL-EXCHANGE KINETICS.

High-pressure studies of solvent viscosity effects on large-amplitude isomerization rates

Abstract The solvent viscosity effects on the intramolecular excimer (IE) formation of 1,3-di-l-pyrenylpropane (DPP) and the ground-state isomerization of 3.3′-diethyloxadicarbocyanine iodide (DODCI) were studied by means of a high-pressure technique. Kramers equation is well applied to the former while it is not to the latter, in which the approach of frequency dependent friction was applied. The activation volume due to solvent dynamical effects (αΔV¦ η) and the intrinsic activation volume (ΔVℷ i) are also determined.

Dynamic solvent effects on activated chemical reactions. I. Classical effects of reaction path curvature

In gas phase reactions, dynamical recrossings across a phase space dividing surface induced by nonlinear reaction path curvature coupling leads to the breakdown of the fundamental dynamical approximation of classical transition state theory (TST). In the following study, we examine the nature of this breakdown for chemical reaction dynamics occurring in solution. As a model system, we consider the collinear A+BC reaction where reaction path curvature increases as the mass of B becomes small compared to the mass of A and C. We use a London–Eyring–Polanyi–Sato (LEPS) potential to describe the solute interaction and model the influence of the solvent by using a generalized Langevin equation that is further represented by a system of coupled harmonic oscillators. Exact classical rate constants are compared to those obtained from conventional TST and canonical variational transition state theory (CVT) as a function of solvent friction coupling. A harmonic TST analysis at the saddle point of the full system (solute plus solvent) with an optimum dividing surface containing both solute and solvent degrees of freedom returns the Grote–Hynes expression for the rate. For the case of no solvent coupling, both TST and CVT are identical and fail to account for the dynamical recrossings induced by reaction path curvature. At intermediate couplings, CVT provides an improvement to the TST estimate and agrees with dynamical simulation results. All estimates of the rate constant approach each other asymptotically at large couplings. The results are interpreted in terms of recrossings in the extended system (solute and solvent coordinates).

Dissociative electron transfer. New tests of the theory in the electrochemical and homogeneous reduction of alkyl halides

In the testing of the theory of dissociative electron transfer with experimental data pertaining to the electrochemical and homogeneous reduction of alkyl halides, uncertainties arising from the estimation of the effect of solvent dynamics and reorganisation as well as of the resonance energy in the transition state are minimized by a comparative strategy which utilizes information derived from outer-sphere electron-transfer data gathered in the same solvent. Application of this strategy leads to a good agreement between theory and experiment in the electrochemical case. In the homogeneous case, the agreement is equally satisfactory in the case of tertiary halides

On the separation of static and dynamic solvent effects for electron transfer reactions

Recent studies of electron transfer (ET) reactions in polar solvents have shown that solvent dynamics, in addition to solvent statics, can have a dramatic effect on the rate. ET reactions were analyzed with the aim of suggesting methods that permit a separation of solvent static and dynamic effects on the rate. Two schemes that can separate these effects are (1) the measurement of ET charge separation (typically a normal regime reaction) and charge recombination (typically an inverted regime reaction) rates in the same solvent and (2) the variation of the static (transition state) rate in a given solvent, as induced by altering the electronic coupling via a series of donor–acceptor complexes at different fixed distances. To emphasize dynamical effects, the static rate contribution should be large, and therefore in the adiabatic, strong electronic coupling limit of Marcus theory. We obtain an expression for the solvent dynamically influenced rate, for the inverted ET regime, which can describe this limit as well as all degrees of electronic coupling. It has the form of a consecutive reaction scheme, the steps being diffusion along the reaction coordinate followed by surface crossing (the static rate contribution), as was obtained previously for the nonadiabatic static rate case.

The general treatment of dynamic solvent effects in electron transfer at high temperature

A general treatment of dynamic solvent effects for outer-sphere electron transfer reactions based on the interactions between the electron transfer system and the solvent bath is presented. The electron transfer rate constant as a function of the solvent longitudinal relaxation time is categorized into the three solvent relaxation regions of adiabatic, normal, and fast. New nonadiabatic effects in the very fast solvent relaxation region are identified. A unified picture for adiabatic and nonadiabatic reactions, as well as a criterion for adiabaticity is given.

Solvent dynamical effects in electron transfer: some predicted modifications in the presence of reactant vibrational activation and comparisons with experiment

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolvent dynamical effects in electron transfer: some predicted modifications in the presence of reactant vibrational activation and comparisons with experimentDonald K. Phelps and Michael J. WeaverCite this: J. Phys. Chem. 1992, 96, 18, 7187–7193Publication Date (Print):September 1, 1992Publication History Published online1 May 2002Published inissue 1 September 1992https://doi.org/10.1021/j100197a013RIGHTS & PERMISSIONSArticle Views44Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (891 KB) Get e-Alerts

Semiclassical theory of the photon echo: Application to polar fluids

The photon echo experiment probes the dynamical processes that cause the decay of a coherent macroscopic electric polarization. Application of the technique to liquid solutions permits the study of the molecular motions that are strongly coupled to an electronic transition. We develop a semiclassical approximation to the photon echo observable, based on the use of Wigner equivalents of quantum operators, that we demonstrate to be accurate for all values of the delay time between the two pulses of the photon echo. In this approximation, the echo arises from fluctuations in the spectroscopic transition frequency, as the fluid evolves on a potential surface that is the arithmetic mean of the ground and excited state surfaces. The echo may then be calculated from nonequilibrium molecular dynamics simulations. We use this method to calculate the photon echo for a fluid of dipolar soft spheres. The results are compared to calculations of the absorption spectrum for this model, and to previous calculations of the effects of solvent dynamics on optical spectroscopic observables.

Energy Gap Dependence of the Solvent Dynamics Effect on Electron Transfer Rates in Non-Linear Response Systems

Energy gap dependences of solvent dynamics effects on the electron transfer rate in polar solutions are investigated by solving the diffusion-reaction equation. New points in this study are that (1) we treat non-linear response systems where the translational motion couples non-linearly with the rotational motion and (2) we investigate systematically the energy gap dependence of the solvent dynamics effect for the charge separation (CS) and charge recombination (CR) reactions. The non-linear free energy functions are characterized, based on the Monte Carlo simulation data for model systems where solvent translational positions are either allowed to move or fixed. The calculated results are that so far as the non-linear coupling is substantial, the energy gap law of the CS reaction is little affected by the solvent dynamics, while that of the CR reaction is greatly modified.

Dynamical solvent effect on the reduction kinetics of cobalt(III) anchored to a mercury electrode via a bridging ligand in water + DMF mixtures

Dynamical solvent effect on the reduction kinetics of cobalt(III) anchored to a mercury electrode via a bridging ligand in water + DMF mixtures

Dynamic solvent effect on the processes of radiationless deactivation of photoexcited molecules: photophysics of dihydroquinolinones

The dynamic effect of a polar (nonreactive) solvent on the rate of electronic relaxation (ER) in polyatomic molecules is analyzed on the basis of the concept of thermal fluctuations of the energy levels involved in the transition initiated by the slow processes of reorientation of the solvent dipoles. The solvent participation in the transition is described by a single collective coordinate with defined relaxation properties. From these properties, an expression for the rate of ER which includes solvent parameters (the reorganization energy and the solvent-induced energy gap) is derived within the harmonic model for the intramolecular oscillators

Vibrational Modes and the Dynamic Solvent Effect in Electron and Proton Transfer

This article primarily reviews recent work on ultrafast experiments on excited state intramolecular electron and proton transfer, with an emphasis on experiments on chemical systems that have been analyzed theoretically. In particular, those systems that have been quantitatively characterized by static spectroscopy, which provides detailed information about the reaction potential energy surface and about other parameters that are necessary to make a direct comparison to theoretical predictions, are described.

Dynamical solvent effects on activated electron-transfer reactions: principles, pitfalls, and progress

Abstract : Recent experimental and conceptual progress in our understanding of dynamical solvent effects in activated electron-transfer processes are critically reviewed. Understanding the various influences exerted by the solvating environment upon the kinetics of electron-transfer (ET) processes, either in homogeneous solution or at metal-solution and related interfaces, has long captured the attention of experimentalists and theoreticians alike. These roles have been perceived primarily in terms of energetic factors, whereby the solvent is considered to affect the reaction rates via its influence on the net activation barrier to electron transfer, delta. Indeed, such considerations form a mainstay of the well-known Marcus and related theoretical treatments. In these approaches, solvent effects upon delta are separated into so-called intrinsic and extrinsic (or thermodynamic) factors. (Author)

Cyclohexane revisited: High pressure nuclear magnetic resonance rotating frame relaxation study of the dynamical solvent effects on the conformational isomerization of cyclohexane

The main goal of this study is to extend the dynamic range of isomerization rates for cyclohexane in order to determine with high accuracy whether the barrier height to isomerization is pressure dependent. Therefore, the effect of pressure and temperature on the conformational isomerization of cyclohexane in carbon disulfide solvent has been investigated using the NMR (nuclear magnetic resonance) rotating frame relaxation technique. This technique, used for the first time in pressure studies of chemical exchange, allows the measurement of isomerization dynamics over a wide range of pressures and temperatures. By combining the rotating frame and NMR line shape techniques and generating the isoviscosity plots, it is shown that the barrier height to isomerization is independent of pressure. Since the experimental isomerization rate is accelerated by pressure, the viscosity dependence of the reduced transmission coefficient shows that the isomerization falls into the energy controlled (inertial) regime of the Kramers model in agreement with our earlier experimental findings. These experimental results, as interpreted in terms of stochastic models of isomerization reactions, indicate a strong collisional coupling and the presence of dynamical solvent effects.

Dynamic solvent effects on electron transfer rates in the inverted regime: Ultrafast studies on the betaines

Transient pump–probe measurements have been made on betaine-30, the solvent polarity probe. Betaine-30 is composed of organic donor and acceptor groups, D+A−⇄kethνDA (excited state). The transient data has been analyzed to measure ket, the electron transfer (et) rate constant, in polar solvents for this inverted regime et. The observed rate constant ket,obs in various polar solvents is as much as a factor of 108 larger than is predicted by the standard, classical, implementation of the theory of Sumi and Marcus, using Kjaer and Ulstrup’s estimates for necessary parameters. In contrast, a quantum treatment of the vibrational modes by Jortner and Bixon, which includes the dynamic solvent effect, predicts that the rate should be approximately ket,JB≂1/〈τs〉. This is close to the experimental results (≂1012 s−1) in typical polar aprotic solvents. However, in highly viscous, slowly relaxing solvents, ket,JB≪ket,obs. This is taken as evidence that the efficient coupling modes for the et in these environments is not the ‘‘conventional solvent coordinate.’’ It is shown that a hybrid of the Jortner/Bixon and Sumi/Marcus theories can physically account for the results. The kinetic behavior of betaine-30 in slowly relaxing solvents is shown to be in the ‘‘diffusionless limit’’ of the hybrid, generalized Sumi–Marcus/Jortner–Bixon picture.

Molecular theory of solvation and solvation dynamics in a binary dipolar liquid

Both the equilibrium and the dynamical aspects of solvation of a classical ion in a dense binary dipolar liquid are investigated by using a molecular theory. The theory properly includes the differing inter- and intramolecular correlations that are present in a binary mixture. As a result, the theory can explain several important aspects of the nonideality of equilibrium solvation energy (broadly known as preferential solvation) observed in experiments. We find that the nonideality of solvation depends strongly on both the molecular size and the magnitude of the dipole moment of the solvent molecules. The interactions among the solvent molecules play an important role in determining the extent of this nonideality. The dynamical calculations are based on a generalized Smoluchowski equation which has been used extensively for studies in one component liquid. For binary liquid, our study reveals rich and diverse behavior such as dependencies on the sizes, the transport coefficients and the polar properties of the components. The theory offers a detailed picture of the dependence of the solvation dynamics on the composition of the mixture. It is predicted that the dynamics of solvation in a binary liquid is, in general, nonexponential and that the details of the dynamics can be quite different from those in a one component liquid. In particular, the continuum model is found to be grossly inaccurate in describing the solvation dynamics in binary mixtures and rather extreme conditions are needed to recover the predictions of the continuum model which can be attributed to the nonideality of the solvation. The predicted results are used to study the dynamic solvent effects on the rate of an adiabatic electron transfer reaction in a binary liquid. The theoretical predictions are also compared with the available experimental results.

Solvent dynamical effects in scanning tunneling microscopy with a polar liquid in the gap

The purpose of this note is to extend our initial views by including considerations about the important role played by the solvent dynamics in promoting charge exchange processes in solution

Molecular dynamics simulation of spectral and dynamic solvent effects for electronic transitions of sodium iodide in argon

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular dynamics simulation of spectral and dynamic solvent effects for electronic transitions of sodium iodide in argonI. Benjamin and Kent R. WilsonCite this: J. Phys. Chem. 1991, 95, 9, 3514–3518Publication Date (Print):May 1, 1991Publication History Published online1 May 2002Published inissue 1 May 1991https://doi.org/10.1021/j100162a016RIGHTS & PERMISSIONSArticle Views55Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (589 KB) Get e-Alerts

Solvent dynamical effects in electron transfer: The solvent inertial limit and the predicted influence of quantum effects

Analytical continuum formulations for the solvent inertial frequency, constituting the anticipated zero-friction limit for adiabatic barrier crossing in solvent-controlled electron-transfer processes, are derived and discussed. The role of solvent inertia in solvent dynamical effects is discussed with emphasis on the likely modifications brought about by nuclear tunneling. Approximate formulations suitable for assessing the latter correction in the presence as well as absence of solvent friction are outlined and compared. Numerical calculations are provided that illustrate the partly compensatory influence on the rate-solvent friction dependence resulting from nuclear tunneling together with reaction non-adiabaticity. Such combined quantum effects are anticipated typically to mask the clearcut emergence of solvent inertial effects on electron-transfer reaction dynamics in common low-friction media.

Solvent dynamical effects of polarization diffusion in the rate constant of electron transfer

The theory of electron transfer reactions accounting for the influence of the solvent polarization diffusion on the rate of reaction is developed. It is shown that in the limit when reaction is controlled by the solvent dynamics the effective frequency of the medium fluctuations consists of the sum of two contributions—the contribution of the solvent dipoles rotation and the contribution of the solvent polarization diffusion. The model of charge distribution of the products and reagents of the reaction is suggested in the framework in which the contribution of the polarization diffusion to the electron transfer rate constant is estimated. It is shown that the contribution of the polarization diffusion to the rate constant of reaction can become dominating in those solvents with large enough self-diffusion coefficients of the solvent molecules.