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

The diffusion properties of tetrathiafulvalene (TTF) and its radical cation (TTF.+) have been studied in organic solvents and in eight imidazolium-based ionic liquids (ILs). The values of the diffusion coefficients of TTF and TTF.+ were obtained by using cyclic and steady-state voltammetry (only for TTF) over a range of 293-343 K. The temperature-dependence of the diffusion coefficients gave good conformity to an Arrhenius-type relation. The diffusional activation energies of TTF and TTF.+ in ILs were found to be similar and compared well to the activation energy of viscous flow for the corresponding IL. The diffusion of TTF.+ in ILs was slower than that of TTF. The ratio in the diffusion coefficients of TTF.+ and TTF at 293 K was observed to be 0.43-0.62 in five ILs, as compared to 0.90 in acetonitrile. The diffusion of TTF and TTF.+ was described using the Stokes-Einstein and Sutherland models.