Solvatochromic Absorbance Probe Behavior within Mixtures of the Ionic Liquid 1‑Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide + Molecular Organic Solvents Anwar Ali,* ,† Maroof Ali, ‡ Nisar Ahmad Malik, † Sahar Uzair, † and Abbul Bashar Khan § † Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi 110025, India ‡ Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India § Center for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia (Central University), New Delhi 110025, India ABSTRACT: The solvent mixtures made up of ionic liquid and molecular solvents have potential applications in various fields such as chemical analysis and synthesis. Thus, in the present study, the role of the solvent microsphere in changing the behavior of the solvatochromic absorbance probe within binary solvent mixtures of ionic liquids with common molecular organic solvents is explored. Further, the behavior of the probes is explained with the help of solute-solvent and solvent- solvent interactions present in the mixtures. The binary mixtures of the ionic liquid 1- butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][Tf 2 N], with molecular solvents, polar protic (methanol, 1-butanol) and polar aprotic (dimethyl sulfoxide, and N,N-dimethylformamide), have been selected for this investigation. The effect of the addition of molecular solvents to ionic liquid’s polarity parameters, E T N , and Kamlet Taft parameters, the hydrogen bond donor ability (HBD) (α), hydrogen bond acceptor ability (HBA) (β), and dipolarity/polarizability (π*), is investigated. The polarity parameters, E T N , and dipolarity/polarizability (π*) of the mixtures indicate the “hyperpolarity” behavior on addition of molecular solvents to ionic liquid. The preferential solvation model has been used to provide insight on the solvent-solvent and/or solute-solvent interactions in the solvent mixtures. 1. INTRODUCTION Ionic liquids (ILs), the potentially green solvents, are a subject of main interest of the scientific and academic community due to their unusual features and vast range of applications in various fields. 1-10 ILs are made up of bulky organic cations and inorganic anions mainly and show a wide range of the physicochemical properties depending upon cations and anions and so are called tunable solvents. ILs have been used as solvents and as catalysts in many organic/inorganic/organo- metallic reactions. 10-15 ILs have also shown their importance in analytical chemistry and have been used in several analytical techniques such as in gas chromatography (GC), high- performance liquid chromatography (HPLC), or mass spectrometry and in electroanalysis, in separation techniques, and for sensing. 16-18 Recently, many research groups have demonstrated the effectiveness of the ILs in changing the photochemical and photophysical behavior of the solutes. 19-24 The importance of the ILs in biocatalysis and biotechnological fields has also been demonstrated by several groups. 25 Besides the aforementioned chemical and biochemical applications of ILs, there are certain limitations also associated with these solvents. One crucial limitation is the limited solubility of many organic and inorganic solutes in these solvents which hampers the full utilization of these solvents in various important fields. 2,5-7 Thus, altering the physicochem- ical properties of ILs with molecular solvents is an area of interest. The solute solubility may enhance in several cosolvent modified IL systems, and the addition of cosolvent may alter the physicochemical properties of solvent mixtures in a favorable manner. As a result, the researchers have started the use of IL + molecular solvent mixtures as solvent media for several chemical applications. 26-28 Toward this end, many research groups have studied the changes in the physicochem- ical properties and also explored solute-solvent and solvent- solvent interactions present in the IL + molecular solvent mixtures. Pandey and Fletcher reported the behavior of the solvatochromic probes in the [bmim][PF 6 ] + ethanol and + water/ethanol mixtures. 29,30 Kumar and Khupse studied the probe behavior in mixtures of ILs with methanol, water, and dichloromethane. 31 Gholami et al. explored the solvatochromic parameters for binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate with water, methanol, and ethanol. 32 In another study, Gholami et al. investigated probe behavior in the solvent mixtures of 2-hydroxyethylammonium formate with N,N-dimethylformamide, dimethyl amine, and dimethyl sulf- oxide. 33 Moita et al. recently demonstrated the absorbance probe behavior of the IL + ethanol solutions. 34 Fortunato and Mancini et al. reported the molecular level behavior of the Received: October 12, 2013 Accepted: April 17, 2014 Published: May 2, 2014 Article pubs.acs.org/jced © 2014 American Chemical Society 1755 dx.doi.org/10.1021/je400908z | J. Chem. Eng. Data 2014, 59, 1755-1765