Diffusion of tetrathiafulvalene and its radical cation in ionic liquids in comparison to conventional solvents

A Binary Mixture of Ionic Liquids as a New Approach for an Experimental Diffusion Correction in the Study of Activated Processes

A binary system of two ionic liquids, 1-ethyl-3-methylimidazolium and trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf₂ ] and [OMA][NTf₂ ], respectively), with varying molar fractions, is introduced. It allows the dynamic viscosity to remain constant over a range of almost 60 K; this means that any activated process can be studied independent of the temperature dependence of viscosity itself. This principle is proven upon reinvestigation of electron self-exchange kinetics of tetrathiafulvalene by continuous-wave ESR line-broadening experiments. From these results, it is also confirmed that this process is totally diffusion controlled.

Dependence of cobaltocenium diffusion in ionic liquids on the alkyl chain length of 1-alkyl-3-methylimidazolium cations

The electrochemical behavior of cobaltocenium (Cc(+)) on a Au(111) electrode was investigated in five 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([Cnmim][Tf2N], n = 2, 4, 6, 8, or 10) ionic liquids (ILs) in the temperature range from 293.15 to 343.15 K by cyclic voltammetry and chronoamperometry. The redox couple of Cc(+) exhibited a clear reversible one-electron reaction in all the [Cnmim][Tf2N] ILs. The diffusion coefficients of Cc(+) increased with an increase in the alkyl chain length of [Cnmim](+) and a decrease in the viscosity of the IL upon elevating the temperature. The viscosity of the IL plays an important role in determining the activation energy for the diffusion of Cc(+). The obtained results suggested that the alkyl chain length of [Cnmim](+) affects the strength of the interaction between Cc(+) and the surrounding ion species. The results also clarified that the equation proposed by Sutherland adequately describes the diffusion of Cc(+) in ILs when the effect of the type of IL and the temperature on the product of the Stokes radius of Cc(+) and the Sutherland coefficient is considered.