Applications of ionic liquids in biphasic separation: Aqueous biphasic systems and liquid-liquid equilibria.

Ionic liquids (ILs) have been receiving much attention in many fields of analytical chemistry because of their various interesting properties which distinguish them from volatile organic compounds. They offer both directional and non-directional forces towards a solute molecule and therefore act as excellent solvents for a wide range of polar and non-polar compounds. Because of the presence of various possible interactions, ILs easily undergo biphasic separation with water and other less polar/non-polar organic solvents.

Ionic Liquid-Based Optical and Electrochemical Carbon Dioxide Sensors.

Due to their unusual physicochemical properties (e.g., high thermal stability, low volatility, high intrinsic conductivity, wide electrochemical windows and good solvating ability), ionic liquids have shown immense application potential in many research areas.

Fluorescein prototropism within poly(ethylene glycol)s and their aqueous mixtures.

Depending on the solubilizing milieu and conditions, fluorescein may exist in one or more of its many prototropic forms [cationic, neutral (zwitterionic, quinoid, and lactone), monoanionic (phenolate and carboxylate), and dianionic]. Fluorescein prototropism is investigated in liquid poly(ethylene glycol)s (PEGs) of different average molecular weight (MW) and their aqueous mixtures using UV-vis absorbance along with static and time-resolved fluorescence spectroscopic techniques. Information regarding various prototropic forms of fluorescein in up to 30 wt % different average MW PEG-added aqueous buffers at varying pH reveals that addition of PEG causes lactonization of fluorescein in the milieu; higher the average MW of PEG, the more the lactonization is.

Fluorescent probe studies of polarity and solvation within room temperature ionic liquids: a review.

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.

Optically responsive switchable ionic liquid for internally-referenced fluorescence monitoring and visual determination of carbon dioxide.

Modulation in the local viscosity and polarity within a reversible carbamate ionic liquid system forms the basis for the fluorescence excimer-based estimation of CO(2). Inherently self-referencing, the photonic response to CO(2) recognition shows excellent sensitivity and complete reversibility, making possible a striking visual display discernible to the naked eye.

Binding of the ionic liquid cation 1-alkyl-3-methylimidazolium to p-tetranitrocalix[4]arene probed by fluorescent indicator displacement.

Acridine orange (AO) was used as a fluorescent probe molecule to study the encapsulation of an alkylimidazolium cation from a water-soluble ionic liquid (IL) within two cavitand species, p-tetranitrocalix[4]arene (1) and calix[4]resorcinarene (2), both in alkaline aqueous media. The addition of IL to the preformed [1·AO] adduct resulted in significantly increased fluorescence due to the expulsion of AO from the inclusion complex to the aqueous phase by competitive recognition of the 1-alkyl-3-methylimidazolium cation ([C(n)mim](+), n = 4 and 6) by 1. Conversely, the fluorescence signal dropped upon the addition of IL to the [2·AO] host-guest complex due to unfavorable binding between [C(n)mim](+) and 2.

Pronounced hydrogen bonding giving rise to apparent probe hyperpolarity in ionic liquid mixtures with 2,2,2-trifluoroethanol.

The fascinating and attractive features of ionic liquids (ILs) can be considerably expanded by mixing with suitable cosolvents, opening their versatility beyond the pure materials. We show here that mixtures of the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and 2,2,2-trifluoroethanol (TFE) display the intriguing phenomenon of hyperpolarity, examples of which are notably sparse in the literature. From the perspective of the E(T)(N) polarity scale and Kamlet-Taft parameters for hydrogen bond acidity (α) and basicity (β), the polarity of this mixture exceeds that of either neat component.

Contrasting behavior of classical salts versus ionic liquids toward aqueous phase J-aggregate dissociation of a cyanine dye.

The effect of addition of ionic liquids (ILs) on the aggregation behavior of a cyanine dye, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), was investigated. In basic aqueous buffer solutions (pH ≥ 10), TDBC preferably exists in its J-aggregated form. Addition of hydrophilic ILs > 5 wt % is observed to disrupt the TDBC J-aggregates, converting them to monomer form most likely because of the interaction between bulky IL cation and the J-aggregates in a time-dependent fashion.

Novel dansyl-appended calix[4]arene frameworks: fluorescence properties and mercury sensing.

Covalently-attached fluorophores may impart enhanced chemosensing capabilities to calixarene frameworks. Synthesis and characterization of six novel dansyl-appended calix[4]arenes, namely, H/Dan4, NO2/Dan4, H/(OH)2Dan2, H/(Ester)2(Dan)2, t-Bu/(OH)2Dan2, and t-Bu/(Ester)2Dan2, containing two or four dansyl moieties are reported. Among these, fluorescence intensity of NO2/Dan4 is observed to decrease significantly in the presence Hg2+ in the solution.

Quenching of pyrene fluorescence by calix[4]arene and calix[4]resorcinarenes.

Interactions involving calixarene and its derivatives are of major importance due to their widespread applications as unique hosts. Fluorescence from a common probe pyrene is used to study interactions involving calix[4]resorcinarene [1a] and its tetra-morpholine derivative [1b] in 1 M aqueous NaOH. These compounds efficiently quench the pyrene fluorescence.

A new class of cationic surfactants inspired by N-alkyl-N-methyl pyrrolidinium ionic liquids.

A series of N-alkyl-N-methylpyrrolidinium halide salts have been synthesized and investigated as potentially useful and tunable detergents for a variety of applications.