X-ray photoelectron spectroscopy of pyrrolidinium-based ionic liquids: cation–anion interactions and a comparison to imidazolium-based analogues

Abstract

We investigate seven 1-alkyl-1-methylpyrrolidinium-based ionic liquids, [C_nC₁Pyrr][X], using X-ray photoelectron spectroscopy (XPS). The electronic environment for each element is analysed and a robust fitting model is developed for the C 1s region that applies to each of the ionic liquids studied. This model allows accurate charge correction and the determination of reliable and reproducible binding energies for each ionic liquid studied. The electronic interaction between the cation and anion is investigated for ionic liquids with one and also two anions. i.e., mixtures. Comparisons are made to imidazolium-based ionic liquids; in particular, a detailed comparison is made between [C₈C₁Pyrr][X] and [C₈C₁Im][X]⁻, where X^¬ is common to both ionic liquids.