Fluorescence study on the structure of ionic liquid aggregates in aqueous solutions

Area of Science:

• Physical Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Ionic liquids are known for cation self-assembly into micelles.
• Anion self-assembly in ionic liquids has not been previously reported.
• Understanding self-assembly is crucial for designing novel materials.

Purpose of the Study:

• To investigate the intrinsic fluorescence of tosylate anions in aqueous solutions.
• To analyze the self-assembly behavior of tosylate anions in p-toluenesulfonic acid (pTSA) and 1-ethyl-3-methylimidazolium tosylate ([emim][TOS]).
• To elucidate the impact of ion pairing on anion aggregation and photophysical properties.

Main Methods:

• Analysis of intrinsic fluorescence and absorption spectra of tosylate.
• Comparison of photophysical behavior in pTSA and [emim][TOS] across various concentrations.
• Spectroscopic characterization to identify monomer and excimer emissions and aggregate formation.

Main Results:

• Tosylate anions in both pTSA and [emim][TOS] exhibit aggregation, forming J aggregates at higher concentrations (>0.1 M).
• [emim][TOS] shows evidence of ion pair formation, distinct from the behavior of pTSA.
• Differences in absorption and excitation spectra indicate aggregation-induced fluorescence enhancement.

Conclusions:

• This study provides the first evidence of anion self-assembly in ionic liquids.
• Anion aggregation significantly influences the photophysical properties of tosylate.
• The findings open new avenues for understanding and controlling self-assembly in ionic liquid systems.