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A spectroscopic analysis of ionic liquid properties : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nanoscience at Massey University, Manawatū, New Zealand
The use of ionic liquids in chemical processes is becoming of increasing
interest, due to the low volatility of ionic liquids, and the wide range of properties
which they possess. The ability to select properties based on anion and cation
choice is also desirable. As such, the development of a solvent reorganization
energy scale incorporating both common organic solvents and ionic liquids is
useful, as it can be used to determine appropriate ionic liquid replacements of
common organic solvents for use in applications.
Raman spectroscopy studies have been performed on solutions of the
solvatochromic Reichardt’s dye in a selection of common organic and ionic liquid
solvents. Due to the solvatochromism of Reichardt’s dye, it behaves differently in
solvents with differing properties. As such, the cross-sections of bands in Raman
spectra associated with Reichardt’s dye differ between solvents also. Modelling of
these cross-sections enables solvent properties to be determined.
Absorption spectra were acquired of each sample, and resonance Raman
spectra of each sample were recorded at a range of excitation wavelengths. After
appropriate data treatment, the absorption and Raman cross-sections were
determined, in order to enable the modelling of absorption and Raman crosssection
profiles. The modelling of these profiles enabled the solvent reorganization
energy of the organic solvents and ionic liquids to be determined, and a relative
scale of solvent reorganization prepared.
Computational studies were performed in order to better understand the
dynamics of Reichardt’s dye in solution. The results from the studies were used to
assign the vibrational modes of the Reichardt’s dye to bands in the resonance
From a solvent reorganization standpoint, it was found that common organic
solvents may be replaced by ionic liquids of similar properties in applications
where solvent volatility is an issue. In addition to this, the information obtained
through the use of the solvent reorganization energy scale is able to be directly
related to applications of ionic liquids involving electron transfer.