Photophysics of 1-Butyl-3-Methylimidazolium Chloride in Aqueous Solution.

M. MIRENDA; BEATRIZ C. BARJA; MARIELA S. ESPINOSA; PAOLA A. BABAY; KARIN GUTKOWSKI

Encuentro; XI Encuentro Latinoamericano de Fotoquimica y Fotobiologia; 2012

Ionic liquids have attracted considerable interest in recent years due to their unique physicochemical properties. One of the most debated issues in the literature concerns the nature of the long tail observed in the absorption spectrum of the imidazolium based ionic liquids, which extends far into the visible region. This long tail, together with a characteristic emission, has been assigned to the presence of aggregated species.[1] However, some authors maintain that the origin of this long tail is due to the presence of impurities, being able to be greatly reduced through different purification processes.[2] Despite the efforts made by several research groups,[3,4] it has not been possible at the moment: a) to obtain a chemical identification of these aggregates or impurities entities and, b) to explain how, in spite of its low concentration, its exerts a remarkable influence on the photophysical properties of these compounds.   In the present work, we carry out studies by irradiation of aqueous solutions of 1-butyl-3-methylimidazolium chloride [BmimCl] with UV-C radiation. We observed the appearance of different absorptions bands between 230 and 350 nm, which are stable at room temperature for several hours. We conducted a detailed characterization of the photo products through UV and IR spectroscopy and HPLC-ESI-MS. The influence of the temperature in the kinetic of the return process ? the disappearance of the absorption bands between 230 and 350 nm - is also presented and discussed.   The irradiation of water solutions of [BmimCl] with UV-C light promotes molecular aggregation and the formation of adducts with the solvent molecules. The description and thorough understanding of these phenomena would seem to be a kick start in clarifying the photophysic of the imidazolium based compounds.