Comparative analysis of dielectric spectra in protic ionic liquids: Experimental findings and computational molecular decomposition

Abstract

Using a combination of experimental measurements and polarizable molecular dynamics simulations, we investigate the dielectric spectra of the protic ionic liquid 1-methylimidazolium acetate, shedding light on their dynamic behavior and intermolecular interactions when adding 1-methylimidazolium trifluoroacetate to increase the fraction of a strong Brønsted acid in the system. The comparison between experimental and computational results provides valuable insights into the accuracy of the simulation models (with and without explicit proton transfer) and the ability to capture the intricate dynamical features of the protic ionic liquid. The investigation revealed complete deprotonation of trifluoroacetate, inducing a shift in the ionic liquid towards a more pronounced ionic state. The computational decomposition of the dielectric spectra into molecular translational and rotational contributions unveiled a reduction in the dielectric constant. This reduction was primarily ascribed to a decrease in translational contributions. Additionally, a strong correlation of the mutual orientation of molecules was found. The observed rise in conductivity upon the addition of 1-methylimidazolium trifluoroacetate to the system was attributed to an increase in proton transport.