Individual tuning of solvent parameters - from organic solvents to ionic liquids

For more than 20 years, we have investigated electron transfer reactions of various types and under various conditions. According to the Marcus theory, solvent parameters have a significant influence on the observed kinetics. Temperature-dependent measurements, such as those used to obtain activation parameters, are especially strongly affected by these influences. Typically, all solvent parameters (e.g., viscosity, density, refractive index, dielectric constant) change systematically as the temperature changes. Therefore, the analysis of kinetic data is difficult. One way to overcome this difficulty is to apply solvent mixtures. In this paper, a detailed description is provided of how one single solvent parameter can be changed while the all others are kept nearly constant. Three different approaches were taken: First, the viscosity was altered at a constant temperature while maintaining the refractive index and dielectric constant. Second, dielectric constant was altered at a constant temperature while maintaining a constant viscosity and refractive index. Finally, all parameters were maintained while the temperaturewas varied. The latter approach offers the possibility to study activation parameters, e.g., by applying the Arrhenius equation, regardless of the viscosity changes that occur when the reaction temperature increases. (C) 2021 The Author(s). Published by Elsevier B.V.