Understanding the Nature of Heterogeneous Electron Transfer in Molecular and Ionic Solvents: Experiment, Theory, and Computations

Abstract

We report a combined experimental and computational study on the heterogeneous electron transfer kinetics for a simple one electron transfer reaction (ferrocene/ferrocenium Fc+/Fc couple) in a series of molecular solvents and ionic liquids. We focus on the diagnostics of the electron transfer regime (adiabatic vs nonadiabatic) and assess the parameters of the quantum mechanical electron transfer theory, which determine the observed tendencies in the solvent effect on the electron transfer rates. The applicability of the linear plots of the electron transfer rate constant vs longitudinal relaxation time (or solvent viscosity) for distinguishing between different ET kinetic regimes is analyzed. Classical molecular dynamics simulations were performed to calculate the potential of mean force for Fc and Fc+. The structure of the reaction layer derived from molecular dynamics is thoroughly investigated. The experimental dielectric spectra for the both type of solvents are used for quantum corrections of the outer-sphere reorganization energy as well as for estimations of the effective frequency factor in the limit of strong and weak electronic coupling. The electron transfer rate constants are calculated and discussed in the viewpoint of available experimental data.

Computational Electrosynthesis Study of Anodic Intramolecular Olefin Coupling: Elucidating the Role of the Electrical Double Layer

“…These PMF calculations are done for both the neutral and cation radical oxidation states, thus providing insight into both the first and second electron transfer/oxidation processes during the electrochemical reaction (Figure ). Note that these PMFs/free energy profiles correspond to the so-called “work terms” invoked in double-layer/Frumkin corrections to heterogeneous electron transfer rate constants. ,− In Figure , we show PMFs computed for both +0/+1 oxidation states of 1-methoxy-1,6-octadiene, as a function of distance from the anode surface. Figure a shows PMFs computed in the Li + /ClO 4 – /MeOH electrolyte, and Figure b shows PMFs computed in the TEMA + /BF 4 – /ACN electrolyte.…”

“…To preface the discussion, it is important to note that bulky, organic molecules within energy-dense solvents may exhibit strong affinities for carbon/electrode surfaces due to solvophobic forces. For example, prior molecular dynamics studies have computed association free energies ranging from ∼10–30 kJ/mol for ferrocene with Au(111) surfaces in organic solvents, and for dipeptides and small aromatic compounds in water with graphene surfaces. , In the latter cases, the association is clearly due to the hydrophobic effect. However, solvophobic forces are more ubiquitous than just occurring in water solutions and may be expected to play a general role in electrosynthesis, by mediating association of bulky, organic molecules with electrode surfaces in energy-dense electrolytes.…”

Fluorescence “ON–OFF–ON” response in the formation of a tetrahedral anionocage and encapsulation of halogenated hydrocarbons

“…38 The quenching of fluorescence intensity was ascribed to electron transfer (eT) from the carbonyl oxygen atoms of urea groups to the excited state of triphenylbenzene (the urea groups interact with the phosphate anion through H-bonds and assume a partial negative charge). 38 Due to the obvious impact of solvent reorganization dynamics in the eT process, 39,40 we reasoned that low temperature fluorescence spectroscopy could provide evidence to demonstrate the eT process for the fluorescence quenching in this work. Fluorescence measurement was then carried out by decreasing the temperature of the system below the freezing point of DMSO to shift the free-energy barrier.…”

Copper Deposition from Chloride-Containing Aqueous Solutions: Catalysis and the Role of the Water Structure

“…Finally, we estimate the rate constants for the first ET step combining the data of MD simulations, quantum chemical calculations, as well as the results obtained by us previously, see ref . A similar approach was employed recently for the analysis of heterogeneous kinetics of the Fc/Fc + redox couple in various solvents . Emphasis is put on qualitative aspects of the problem, i.e., the catalytic effect of the Cl – anions on copper deposition.…”

“…A similar approach was employed recently for the analysis of heterogeneous kinetics of the Fc/Fc + redox couple in various solvents. 12 Emphasis is put on qualitative aspects of the problem, i.e., the catalytic effect of the Cl − anions on copper deposition.…”