Fluorescent Probe Studies of Polarity and Solvation within Room Temperature Ionic Liquids: A Review

Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, USA.
Journal of Fluorescence (Impact Factor: 1.93). 06/2012; 22(5):1313-43. DOI: 10.1007/s10895-012-1073-x
Source: PubMed


Ionic liquids display an array of useful and sometimes unconventional, solvent features and have attracted considerable interest in the field of green chemistry for the potential they hold to significantly reduce environmental emissions. Some of these points have a bearing on the chemical reactivity of these systems and have also generated interest in the physical and theoretical aspects of solvation in ionic liquids. This review presents an introduction to the field of ionic liquids, followed by discussion of investigations into the solvation properties of neat ionic liquids or mixed systems including ionic liquids as a major or minor component. The ionic liquid based multicomponent systems discussed are composed of other solvents, other ionic liquids, carbon dioxide, surfactants or surfactant solutions. Although we clearly focus on fluorescence spectroscopy as a tool to illuminate ionic liquid systems, the issues discussed herein are of general relevance to discussions of polarity and solvent effects in ionic liquids. Transient solvation measurements carried out by means of time-resolved fluorescence measurements are particularly powerful for their ability to parameterize the kinetics of the solvation process in ionic liquids and are discussed as well.

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    ABSTRACT: Activity coefficients at infinite dilution (γ1,2 ∞) for 40 diverse probe solutes, including various (cyclo)alkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, thiophene, ethers, nitroalkanes, and ketones, were measured by inverse gas chromatography at temperatures from 323 to 343 K in three homologous 1-alkyl-1- methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs), bearing hexyl, octyl, and decyl side chains. The retention data were further converted to gas-to-IL and water-to-IL partition coefficients using the corresponding gas-to-water partition coefficients. Both sets of partition coefficients were analyzed using the modified Abraham solvation parameter model, with the derived equations tightly correlating the experimental gas-to-IL and water-to-IL partition coefficient data to within average standard deviations of 0.088 and 0.111 log units, respectively. © 2012 American Chemical Society.
    Journal of Chemical & Engineering Data 12/2012; 57(12-12):3510-3518. DOI:10.1021/je300692s · 2.04 Impact Factor
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    ABSTRACT: In this work, we report the infinite dilution activity coefficients (γ1,2∞) of 39 to 43 diverse organic solutes dissolved in three 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids (IL) homologues bearing propyl, butyl, and pentyl n-alkyl side chains, respectively, as determined by inverse gas chromatography at temperatures from 323 K to 343 K. The organic solutes include various (cyclo)alkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, thiophene, ethers, nitroalkanes, and ketones. The measured retention data were further transformed to gas-to-IL and water-to-IL partition coefficients using established thermodynamic approaches based upon the corresponding gas-to-water partition coefficients of the test solutes. Both sets of partition coefficients were interpreted with a modified form of the basic Abraham general solvation parameter model. The mathematical correlations obtained by regression analysis back-calculated the observed gas-to-IL and water-to-IL partition coefficient data to within average standard deviations of 0.104 and 0.136 log units, respectively.
    Journal of Chemical & Engineering Data 07/2013; 58(8):2210–2218. DOI:10.1021/je4001894 · 2.04 Impact Factor
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    ABSTRACT: In recent years, the effect of molecular charge on the rotational dynamics of probe solutes in room temperature ionic liquids (RTILs) has been a subject of growing interest. For the purpose of extending our understanding of charged solute behavior within RTILs, we have studied the rotational dynamics of three illustrative xanthene fluorescent probes within a series of N-alkylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Cnmpyr][Tf2N]) RTILs with different n-alkyl chain lengths (n = 3, 4, 6, 8, or 10) using time-resolved fluorescence anisotropy decay. The rotational dynamics of the neutral probe rhodamine B (RhB) dye lies between the stick and slip boundary conditions due to the influence of specific hydrogen bonding interactions. The rotation of the negatively-charged sulforhodamine 640 (SR640) is slower than that of its positively-charged counterpart rhodamine 6G (R6G). An analysis based upon Stokes-Einstein-Debye hydrodynamics indicates that SR640 adheres to stick boundary con-ditions due to specific interactions, whereas the faster rotation of R6G is attributed to weaker electrostat-ic interactions. No dependence of the rotational dynamics on the solvent alkyl chain length was ob-served for any of the three dyes, suggesting that the specific interactions between dyes and RTILs are independent of this solvent parameter.
    The Journal of Physical Chemistry B 01/2014; 118(4). DOI:10.1021/jp4107553 · 3.30 Impact Factor
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