Effect of microheterogeneity in room temperature ionic liquids on energy and electron transfer processes (original) (raw)
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Chemphyschem : a European journal of chemical physics and physical chemistry, 2017
The impact of temperature-induced changes in solvent dynamics on the diffusion coefficient and standard rate constant k(0) for heterogeneous electron transfer (ET) of ethylferrocene (EFc) in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6 ]) is investigated. The results are analysed to understand the impact of solvent-dynamic control, solute-solvent interactions and solvent friction on the transport of redox probes and k(0) . Concentration dependence of the diffusion coefficient of EFc in [BMIM][PF6 ] is observed. This is attributed to the solute-induced enhancement of the structural organisation of the ionic liquid (IL), which is supported by the concentration-dependent UV/Vis absorption and photoluminescence responses of EFc/[BMIM][PF6 ] solutions. Similar values of the activation energies for mass transport and ET and a linear relationship between the diffusion coefficient and the heterogeneous ET rate is observed. The ratio between the diffusion coefficient and the h...
Zeitschrift für Physikalische …
Room temperature ionic liquids (RTILs) are of growing interest due to their outstanding solvent properties. The high conductivity and large electrochemical window of RTILs have enabled their use in electrochemistry without adding supporting electrolyte. Heterogeneous electron transfer rate constants (k het ) and diffusion coefficients (D) of ferrocene, 2,6-dimethylbenzoquinone, bromanil, tetracyanoethylene, tetrathiofulvalene, methylviologen, and ethylviologen were determined in several RTILs such as [emim][BF 4 ], [bmim][OTf], [bmim][BF 4 ] and [bmim] [PF 6 ] using cyclic voltammetry. The results obtained for k het and D, range from 0.25-29.6 × 10 −4 cm s −1 and 1.27-25.5 × 10 −8 cm 2 s −1 respectively. Both were significantly lower than those found in organic solvents like acetonitrile (MeCN), dimethylformamide (DMF), etc. It was found that k het and D were two to three orders of magnitude lower in more viscous RTILs. Diffusion coefficients were inversely proportional to the viscosity of the RTILs for all substances under investigation. Marcus theory was applied to compare the k het . The main problem arising is to understand the role of solvent reorganization energy (λ o ). Whereas Marcus theory describes λ o in two parts of polarization, a fast electronic and a slower orientational contribution both expressed by the Pekar factor γ = (1/n 2 − 1/ε s ), the solvent is treated as a continuum having a dielectric constant (ε s ) and a refractive index (n). Such a concept seems to be not applicable to ionic liquids.
Accounts of Chemical Research, 2007
A brief account of recent simulation and theoretical model studies of various solution-phase processes in room-temperature ionic liquids is given. These include structure and dynamics of equilibrium and nonequilibrium solvation, solute rotation and vibrational energy relaxation, and free energetics and dynamics of unimolecular electron-transfer reactions. Special attention is paid to both the aspects shared by and the contrasts with polar solvents under normal conditions. A brief comparison with available experiments is also made. CO. In 1992, he joined the faculty of Carnegie Mellon University, where he is currently a Professor of Chemistry. He is also an adjunct faculty member of the Department of Physics, Korea University. His research theme centers around equilibrium and nonequilibrium statistical mechanics of solution systems and chemical reaction dynamics in condensed phases.
Hindered Intramolecular Electron Transfer in Room-Temperature Ionic Liquid
The Journal of Physical Chemistry B, 2010
have been desgined and prepared. Their photophyscial properties in room-temperature ionic liquid (RTILs) were studied by steady-state absorption and emission spectra and fluorescence lifetime measurements. The intramolecular photoinduced electron transfer from dimethylamine to PDI in 1 and 2 has been efficiently hindered because of the solvation of RTILs. A two-conformation mechanism for the PET in 1 and 2 is proposed, which explains the results of the fluorescence lifetime measurements well. The solvation of RTILs to 3 resembled that of a normal polar organic solvent with polarity larger than that of DMF.
We report the anodic oxidation of several arenes and anthracenes within room-temperature ionic liquids (RTILs). In particular, the heterogeneous electron-transfer rates (k0) for substituted anthracenes and arenes are also investigated in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) and found not to obey the outer-sphere Marcus-type behavior of these compounds in contrast to the behavior in traditional organic solvents, in particular the predictions for k0 with molecular size and solvent static dielectric constant. To obtain the electron-transfer rate for 9-phenylanthracene, the dimerization and heterogeneous electron-transfer kinetics of its electrogenerated radical cations is studied in [C2mim][NTf2] and eight other RTILs and are both found to be largely independent of the solution viscosity. http://pubs.acs.org/doi/abs/10.1021/jp7103598
The Journal of Physical Chemistry C, 2019
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 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.