Synchrotron-based UV resonance Raman scattering for investigating ionic liquid-water solutions

TL;DR

This study demonstrates that synchrotron-based UV resonance Raman spectroscopy effectively probes local structures and intermolecular interactions in ionic liquids and their water solutions, offering advantages over spontaneous Raman methods.

Contribution

It introduces UVRR spectroscopy as a selective, sensitive tool for investigating structural modifications in ionic liquids caused by different anions, alkyl chains, and water addition.

Findings

UVRR signals are sensitive to anion changes.

Longer alkyl chains affect local structure.

Water influences cation-anion hydrogen bonding.

Abstract

This work shows that bulk ionic liquids (ILs) and their water solution can be conveniently investigated by synchrotron-based UV resonance Raman (UVRR) spectroscopy. The main advantages of this technique for the investigation of the local structure and intermolecular interactions in imidazolium-based ILs are presented and discussed. The unique tunability of synchrotron source allows one to selectively enhance in the Raman spectra the vibrational signals arising from the imidazolium ring. Such signals showed good sensitivity to the modifications induced in the local structure of ILs by i) the change of anion and ii) the progressively longer alkyl chain substitution on the imidazolium ring. Moreover, some UVRR signals are specifically informative on the effect induced by addition of water on the strength of cation-anion H-bonds in IL-water solutions. All of these results corroborate the potentiality of UVRR to retrieve information on the intermolecular interactions in IL-water solutions, besides the counterpart obtained by employing on these systems the spontaneous Raman scattering technique.