Solvent Reorganization Entropy of Electron Transfer in Polar Solvents

Abstract

We report the results of molecular dynamics simulations of the solvent reorganization energy of intramolecular electron transfer in a charge-transfer molecule dissolved in water and acetonitrile at varying temperatures. The simulations confirm the prediction of microscopic solvation theories of a positive reorganization entropy in polar solvents. The results of simulations are analyzed in terms of the splitting of the reorganization entropy into the contributions from the solute-solvent interaction and from the alteration of the solvent structure induced by the solute. These two contributions mutually cancel each other, resulting in the reorganization entropy amounting to only a fraction of each component.

Dynamical Arrest of Electron Transfer in Liquid Crystalline Solvents

“…Because, for large solutes with the effective radius R 0 . σ, the range of k values affecting solvation is k < π/R 0 , the approximation S L -(k) = S L (0), resulting in continuum solvation, is reasonably accurate (deviations from this approximation are responsible for observable effects on the solvation entropy 54,55 ). The perpendicular component S xx (k) in liquid crystals is governed by repulsions of long molecular rods at the distance of shortaxis diameter = σ and is, therefore, qualitatively similar to S L -(k) in isotropic solvents.…”

“…The slope of the continuum free energy is, however, incorrect, as is often the case with continuum calculations of the solvation entropy. [54][55][56]58 …”

Energetics of Electron-Transfer Reactions in Soft Condensed Media

“…This positive intercept is related to a positive value of the reorganization entropy, which can be measured either at constant volume (subscript "V") or at constant pressure (subscript "P") Which entropy, S P or S V , is larger is controlled by the sign of the isobaric expansivity of the solvent: S P > S V at positive expansivity (as in Figure 2) and S P < S V at negative expansivity. 18 The quasi-macroscopic character of the dipolar solvent response is caused by the long range of electrostatic solute-solvent and dipolar solvent-solvent interactions. When either of the two is more short-ranged, the cancellation between single-particle and two-particle parts of the response is not perfect and the solvent response bears more microscopic features.…”

Non-Gaussian statistics of binding/unbinding events and the energetics of electron transfer reactions

“…5 is not the only data point potentially supporting the present model. Our recent numerical simulations of the energetics of charge-transfer within a small charge-transfer molecule p-nitroaniline gave results unexplainable by traditional models [29]. The reorganization energies for the forward and backward electronic transitions in p-nitroaniline turned out to be equal, k 1 ¼ k 2 , as expected in the Marcus-Hush picture of equal-curvature parabolas.…”