High conductivity and low viscosity Brønsted acidic ionic liquids with oligomeric anions

Two series of Brønsted acidic room temperature ionic liquids (RTILs) comprising of oligomeric anions and cyclic amine based cations are prepared. All RTILs studied here are liquids and have a high ionic conductivity (up to 20.96 mS/cm) and a low viscosity (down to 10.4 mPa s) at room temperature. The incorporation of oligomeric anions in ILs significantly increases the density and conductivity, and decreases the viscosity. The temperature-dependent electrolyte viscosity with molar conductivity is correlated through applying an empirical Walden's rule. A relatively larger deviation of the plots from the “ideal” Walden line is observed for the ILs synthesized by equal molar acid and base, although the deviation decreases significantly when the ILs contain oligomeric anions. Spectroscopic measurements of solvatochromic probe molecules in RTILs provide insights into solvent intermolecular interactions through interpretation of the different and generally uncorrelated polarity scales.