Influence of the Electric Charge of Spin Probes on Their Diffusion in Room-Temperature Ionic Liquids

Abstract

The rotational and translational diffusion of negatively charged and uncharged spin probes in five imidazolium-based room-temperature ionic liquids (RTILs), 1-ethyl-3methylimidazolium tetrafluoroborate, emimBF 4 , 1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF 4 , 1-octyl-3-methylimidazolium tetrafluoroborate, omimBF 4 , 1-octyl-3-methylimidazolium hexafluorophosphate, omimPF 6 , and 1-octyl-3-methylimidazolium chloride, omimCl, has been studied by means of electron paramagnetic resonance spectroscopy. Detailed analyses of the spin-Hamiltonian parameters and spin exchange interactions have been carried out. The temperature dependences of the line broadening induced by the electronic dipole−dipole interaction and the electron spin exchange coupling are determined. The translational mobility of spin probes is semiquantitatively characterized and successfully explained in the framework of a hypothesis based on the assumption of polar and unpolar domains within the RTILs.

High-Pressure ESR Spectroscopy: On the Rotational Motion of Spin Probes in Pressurized Ionic Liquids

“…Many publications have documented deviations from Stokes–Einstein and Stokes–Einstein–Debye (SED) relations in pure ionic liquids and ionic liquid/solvent mixtures. Often these deviations are ascribed to strong solvent–solute interactions and/or differences in size and shape of the RTIL constituents and the molecules investigated. − On the other hand, the SED is based on continuum hydrodynamics and applies to large solutes immersed in a homogeneous environment. In fact, already Einstein pointed out that there is little reason to apply SED-like equations on the molecular scale .…”