Room temperature ionic liquid as a novel medium for liquid/liquid extraction of metal ions

Room temperature ionic liquids (RTILs) have been used as novel solvents to replace traditional volatile organic solvents in organic synthesis, solvent extraction, and electrochemistry. The hydrophobic character and water immiscibility of certain ionic liquids allow their use in solvent extraction of hydrophobic compounds. In this work, a typical room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆], was used as an alternative solvent to study liquid/liquid extraction of heavy metal ions. Dithizone was employed as a metal chelator to form neutral metal-dithizone complexes with heavy metal ions to extract metal ions from aqueous solution into [C₄mim][PF₆]. This extraction is possible due to the high distribution ratios of the metal complexes between [C₄mim][PF₆] and aqueous phase. Since the distribution ratios of metal dithiozonates between [C₄mim][PF₆] and aqueous phase are strongly pH dependent, the extraction efficiencies of metal complexes can be manipulated by tailoring the pH value of the extraction system. Hence, the extraction, separation, and preconcentraction of heavy metal ions with the biphasic system of [C₄mim][PF₆] and aqueous phase can be achieved by controlling the pH value of the extraction system. Preliminary results indicate that the use of [C₄mim][PF₆] as an alternate solvent to replace traditional organic solvents in liquid/liquid extraction of heavy metal ions is very promising.     

Study on the Conductivities of Pure and Aqueous Bromide-Based Ionic Liquids at Different Temperatures

Electrical conductivities were measured for the pure ionic liquids [C₆mim][Br] (1-hexyl-3-methylimidazolium bromide) and [C₈mim][Br] (1-octyl-3-methylimidazolium bromide) at 0.1 MPa from 293.15 to 333.15 K. Conductivity measurements were also made for the binary water + [C₆mim][Br] and water + [C₈mim][Br] systems and their ternary water + [C₆mim][Br] + [C₈mim][Br] system at 0.1 MPa and 293.15, 298.15, and 303.15 K. The conductivity data of the pure ionic liquids were correlated by the VFT (Vogel-Tamman-Fulcher) equation, and the fitting parameters and mean absolute deviations were determined. New explanations are presented for the molality-dependent behavior of the conductivity of the binary water + [C₆mim][Br] and water + [C₈mim][Br] systems. The generalized Young’s rule and the semi-ideal solution theory for conductivity were used to predict the conductivities of the ternary water + [C₆mim][Br] + [C₈mim][Br] system from the conductivities of its corresponding binary water + [C₆mim][Br] and water + [C₈mim][Br] subsystems. The predictions are in good agreement with the measured values.     

离子液体型表面活性剂研究

以1-甲基咪唑为原料, 制备了6个常规离子液体: 1-正丁基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[bmim][BF₄]及[bmim][PF₆])、1-正己基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[hmim][BF₄]及[hmim][PF₆])、1-正十六烷基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[C₁₆mim][BF₄]及[C₁₆mim][PF₆])和4个功能化离子液体: 1-(2-羟乙基)-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[2-hemim][BF₄]及[2-hemim][PF₆])、1-乙氧羰基甲基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[eocmmim][BF₄]及[eocmmim][PF₆]). 研究了这两类离子液体的一些物理性能, 旨在挖掘离子液体在香料香精化妆品工业中的应用价值. 分别检测了它们与一般溶剂的互溶性, 并测定了它们的表面张力和发泡性能, 实验结果表明, 仅[C₁₆mim][BF₄]和[C₁₆mim][PF₆]具有发泡性能, 发泡力分别为68和120 mm.     

Extraction and high performance liquid chromatographic determination of 3-indole butyric acid in pea plants by using imidazolium-based ionic liquids as extractant

In this paper, imidazolium-based ionic liquids [C₄mim][PF₆], [C₆mim][PF₆], [C₈mim][PF₆], [C₆mim][BF₄] and [C₈mim][BF₄] were tested as extracting solvents for removal of 3-indole butyric acid (IBA) from aqueous media with subsequent determination using HPLC. Percent extraction of IBA was strongly affected by pH of aqueous phases and the chemical structures of ionic liquids (ILs). Extraction of IBA was quantitative in the pH values lower than pK_a of IBA. Considering both extraction and stripping efficiencies of IBA, [C₄mim][PF₆] was found to act more efficient than other studied ILs. Capacity of [C₄mim][PF₆] was 17.6 × 10⁻⁴ mmol IBA per 1.0 mL of IL. Ionic strength of aqueous phase and temperature had shown no serious effects on extraction efficiency of IBA. A preconcentration factor of 100 and a relative standard deviation of 1.16% were obtained. It was found that ionic liquid phase was reusable almost five times for extraction/stripping purposes. 3-Indole acetic acid showed interferential effect in the extraction step. In order to assess the applicability of the method, extraction and stripping of IBA from pea plants and some other samples were studied.     

Solubilities of imidazolium-based ionic liquids in aqueous salt solutions at 298.15 K

The solubilities of ionic liquids in the ternary systems (ionic liquid + H₂O + inorganic salt) were reported at 298.15 K and atmospheric pressure. The examined ionic liquids are [C₄mim][PF₆] (1-n-butyl-3-methylimidazolium hexafluorophosphate), [C₈mim][PF₆] (1-n-octyl-3-methylimidazolium hexafluorophosphate), and [C₈mim][BF₄] (1-n-octyl-3-methylimidazolium tetrafluoroborate). The examined inorganic salts are the chloride-based salts (sodium chloride, lithium chloride, potassium chloride, and magnesium chloride) and the sodium-based salts (sodium thiocyanate, sodium nitrate, sodium trifluoroacetate, sodium bromide, sodium iodide, sodium perchlorate, sodium acetate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium tetrafluoroborate, sodium sulfate, and sodium carbonate). The effects of the cations and the anions of the ionic liquids and of the inorganic salts on the solubility of the ionic liquids in the ternary solutions were systematically compared and discussed.     

Reverse ATRP Process of Methacrylonitrile in [C4mim][PF6]

In this original experiment, an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]), was used as the reaction media for reverse atom transfer radical polymerization of methacrylonitrile (MAN) initiated by azobisisobutyronitrile (AIBN) with FeCl₃ and isophthalic acid (IA) as catalyst and ligand. The polymerization in [C₄mim][PF₆] proceeded in a well-controlled manner as evidenced by kinetic studies. Compared with the polymerization in N, N-dimethylformamide (DMF), the polymerization in [C₄mim][PF₆] not only showed better control of molecular weight and narrower molecular weight distribution but also provided more rapid reaction rate with the ratio of [MAN]:[AIBN]:[FeCl₃]:[IA] at 300:1:2:4. The block copolymer PMAN-b-PSt was obtained via a conventional ATRP process in [C₄mim][PF₆] by using the resulting PMAN as macroinitiator. [C₄mim][PF₆] and FeCl₃/IA could be easily recycled and reused and had no effect on the living nature of reverse atom transfer radical polymerization of MAN.     

γ辐照引发[Cnmim][NTf2]离子液体变色研究

1-烷基-3-甲基咪唑双三氟甲基磺酰胺型离子液体(C_nmim][NTf₂])被认为是最有希望用于核燃料循环中的分离试剂之一, 虽然其化学结构在辐照过程中变化不大, 但在受到γ辐照后会发生明显的变色, 因此有必要研究该类离子液体的变色原因. 本文以⁶⁰Co为辐照源, 系统研究了辐照后不同C(1)－烷基链长和咪唑环上C(2)位上的H被甲基取代后离子液体的紫外-可见(UV-Vis)吸收光谱行为, 并结合辐照后离子液体荧光光谱和质谱的变化, 分析了导致该类离子液体辐照后颜色加深的原因. 结果表明, 随着咪唑环上C(1)―烷基链长度和剂量增大, 离子液体颜色加深; 而C(2)位上的H被甲基取代后颜色明显变浅. 辐照后咪唑型离子液体的变色主要来自于辐照后产生的烷基侧链含双键的咪唑阳离子, 咪唑阳离子二聚体和含氟咪唑化合物. 此外, γ辐照引起咪唑阳离子易发生π-π堆积, 而聚集态含量增加也会引起颜色加深.     

Ionic Liquid‐Carbon Nanotube Modified Screen‐Printed Electrodes and Their Potential for Adsorptive Stripping Voltammetry

Compared with paraffin oil, the use of ionic liquids as a binder in carbon paste type electrodes was shown to greatly enhance the accumulation of analytes, as illustrated with 17α‐ethynylestradiol as a model. The ionic “liquid” n‐octyl‐pyridinium hexafluorophosphate [C₈py][PF₆] was most efficient among several ionic liquids investigated. Such preconcentration allowed a [C₈py][PF₆]‐multiwalled carbon nanotubes (MWCNTs) (95 : 5 w/w) composite electrode to be useful for adsorptive stripping voltammetry. Screen‐printed electrodes modified with [C₈py][PF₆]‐MWCNTs were developed and were able to achieve high sensitivity during adsorptive stripping voltammetric measurements under optimised conditions.     

Pd-catalyzed asymmetric alternating co-polymerization of propene with carbon monoxide using ionic liquids

A protocol for Pd-catalyzed stereoselective co-polymerization of propene and carbon monoxide using chiral ligands, such as (2S,3S)-DIOP and (R)-P-Phos in [C₄mim][PF₆]/[C₆mim][PF₆] as an ionic liquid medium was developed. With (2S,3S)-DIOP as chiral ligand and [C₄mim][PF₆] as medium, the Pd-catalyzed co-polymerization of propene and CO gave almost completely regioregular polyketones, and the product polymer showed moderate stereoregularity (61% of ℓ-diads). The highest molar optical rotation = +15.9 and polydispersity = 1.2 were attained when (R)-P-Phos was used as the ligand and [C₆mim]PF₆ as the solvent. The co-polymer exhibited regioregularity of H–H/H–T/T–T (%) = 17:66:17.     

Influence of ionic liquids on actinides extraction by diphenyl(dibutyl)carbamoylmethylphosphine oxide in different solvents from nitric acid solution

Influence of ionic liquids (ILs) addition (1?C50 wt%) on extraction efficiency of actinides by diphenyl(dibutyl)carbamoylmethylphosphine oxide (Ph₂Bu₂) from 3 M HNO₃ has been studied. Am(III) distribution ratios in two-phase systems 0.1 M Ph₂Bu₂ in either DCE or CHCl₃?C3 M HNO₃ depending on the nature of additional ionic liquids: imidazolium-based ILs: [C₄mim][PF₆], [C₄mim][BF₄] and phosphonium-based ILs: PPF₆, PBF₄ and PCl were determined. The highest value of Am(III) extraction ratio change (1040) was found on addition of PPF₆ to Ph₂Bu₂ in CHCl₃. Extraction of Pu(IV) and U(VI) by 0.001 M Ph₂Bu₂ in the presence of [C₄mim][PF₆] in DCE, CHCl₃ or meta-nitrobenzotrifluoride (NBTF) have been investigated. The greatest enhancement of extraction efficiency was observed using CHCl₃, the least polar studied solvent. Using a mixture of conventional solvent and ionic liquid as a solvent for extractant enables one to increase distribution ratios and reduce viscosity of organic phase as compared with ionic liquid viscosity. The marked increase of Am(III), Pu(IV) and U(VI) extraction extent by Ph₂Bu₂ on addition of ionic liquids to the extent of 10 wt% permit one essentially to diminish amounts considerably more expensive carbamoylmethylphosphine oxide(the general name is CMPO) used in TRUEX process.     

Ionic Association of the Ionic Liquids [C4mim][BF4], [C4mim][PF6], and [Cnmim]Br in Molecular Solvents

Considering the ionic nature of ionic liquids (ILs), ionic association is expected to be essential in solutions of ILs and to have an important influence on their applications. Although numerous studies have been reported for the ionic association behavior of ILs in solution, quantitative results are quite scarce. Herein, the conductivities of the ILs [C_nmim]Br (n=4, 6, 8, 10, 12), [C₄mim][BF₄], and [C₄mim][PF₆] in various molecular solvents (water, methanol, 1‐propanol, 1‐pentanol, acetonitrile, and acetone) are determined at 298.15 K as a function of IL concentration. The conductance data are analyzed by the Lee–Wheaton conductivity equation in terms of the ionic association constant (K_A) and the limiting molar conductance (Λ_m⁰). Combined with the values for the Br^? anion reported in the literature, the limiting molar conductivities and the transference numbers of the cations and [BF₄]^? and [PF₆]^? anions are calculated in the molecular solvents. It is shown that the alkyl chain length of the cations and type of anion affect the ionic association constants and limiting molar conductivities of the ILs. For a given anion (Br^?), the Λ_m⁰ values decrease with increasing alkyl chain length of the cations in all the molecular solvents, whereas the K_A values of the ILs decrease in organic solvents but increase in water as the alkyl chain length of the cations increases. For the [C₄mim]⁺ cation, the limiting molar conductivities of the ILs decrease in the order Br^?>[BF₄]^?>[PF₆]^?, and their ionic association constants follow the order [BF₄]^?>[PF₆]^?>Br^? in water, acetone, and acetonitrile. Furthermore, and similar to the classical electrolytes, a linear relationship is observed between ln K_A of the ILs and the reciprocal of the dielectric constants of the molecular solvents. The ILs are solvated to a different extent by the molecular solvents, and ionic association is affected significantly by ionic solvation. This information is expected to be useful for the modulation of the IL conductance by the alkyl chain length of the cations, type of anion, and physical properties of the molecular solvents.     

Viscosities for Ionic Liquid Binary Mixtures with a Common Ion

At present, there is a considerable amount of work devoted to the study of the thermophysical properties of pure ionic liquids, which contrasts with the few data available for their mixtures. One of the most appealing characteristics of ionic liquids is the capability of subtly changing the chemical structure of the cation and anion in order to design appropriate solvents for specific applications. Mixtures of ionic liquids increase enormously this specificity, due to the unlimited combinations that arise from mixing two or more ionic liquids. In this context, the study of the thermophysical properties of these mixtures is revealed as a fundamental task. In this work the viscosities of the ionic liquid binary mixtures with a common ion ([C₆mim] + [C₂mim])[BF₄], ([C₆mim] + [C₄mim])[BF₄], [C₄mim]([BF₄] + [MeSO₄]) and [C₄mim]([PF₆] + [BF₄]) were determined within the temperature range (298.15–308.15) K. The temperature dependence of the viscosity for pure liquids is analyzed by means of the Vogel-Tammann-Fulcher equation and several mixing rules are applied for the mixtures.     

Luminescent Soft Material: Two New Europium‐Based Ionic Liquids

Two new Eu‐based ionic liquid systems, [C₄mim][DTSA] : [Eu(DTSA)₃] and 2[C₄mim] [DTSA] : [Eu(DTSA)₃] were synthesized at 120° under inert conditions from 1‐butyl‐1‐methylimidazolium ditoluenesulfonylamide ([C₄mim][DTSA]). The identity and purity of the synthesized compounds were confirmed by elemental analysis, IR, Raman, and ¹H‐NMR spectroscopy. As they solidify below 100° as glasses they qualify as ionic liquids. Fluorescence measurements show that the materials exhibit a strong red luminescence of high color purity. Therefore, they have the potential to be used for optical applications such as in emission displays.     

Thermodynamic study of interfacial tension between oil and aqueous phases composed of ionic liquids and brine

The first fundamental step in determining the physicochemical properties of an equilibrium system is to determine the activity coefficient of electrolyte and non-electrolyte ions. Based on understanding the importance of activity coefficient in thermodynamic systems in this study, in order to predict interfacial tension between oil and aqueous phases composed of ionic liquids and brine, a modified thermodynamic equation based on concentration and coefficient of activity of ionic liquids is defined. For this study, the Extended UNIQUAC model is desired and its adjustable parameters are optimized with Genetic + PSO algorithm. The modified model has practical features such as investigating the effect of concentrations of salts in the water of oil fields formation on the interfacial tension of the system, investigating the effect of concentrations of various organic compounds such as ionic liquids on the interfacial tension of the system and investigating the interaction energy between organic and inorganic ions. In this study, the optimization of the modified thermodynamic equation to predict the interfacial tension of solutions containing [C₈Py][Cl], [C₁₈Py][Cl], [C₁₂mim][Cl] and [C₁₈mim][Cl] with the presence of brine and distilled water is investigated. Also, the effect of ionic strength of the solution in 32 equilibrium systems on interfacial tension is investigated. According to the optimization results of this study, the design of a computer program can be considered to predict the interfacial tension with the presence of ionic liquids and salts.     

Separation of no-carrier-added 109Cd from natural silver target using RTIL 1-butyl-3-methylimidazolium hexafluorophosphate

The room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆] has various applications in the separation of a range of metal ions replacing volatile and toxic traditional organic solvents in liquid–liquid extraction systems. In this study, the RTIL [C₄mim][PF₆] was used to separate no-carrier-added (NCA) ¹⁰⁹Cd from α-particle irradiated Ag target. A natural Ag foil was bombarded by 30 MeV α-particles to produce ¹⁰⁹Cd. After the decay of all co-produced short-lived products, NCA ¹⁰⁹Cd was separated from the bulk Ag using [C₄mim][PF₆] as extractant from HNO₃ medium. Ammoniumpyrrolidine dithiocarbamate (APDC) was used as a complexing agent. At the optimum condition, 3 M HNO₃, 0.01 M APDC in presence of [C₄mim][PF₆], ~99 % bulk Ag was extracted to the IL phase, leaving NCA ¹⁰⁹Cd in the aqueous phase. The amount of Ag became negligibly small after re-extraction in the same condition. The ionic liquid was recovered by washing it with 1 M HCl.     

[C12mim]Br: A Temperature‐dependent Phase Transfer Catalyst and Its Application for Aerobic Oxidative Synthesis of 2‐Aryl Benzimidazoles,Benzoxazoles or Benzothiozoles Catalyzed by TEMPO Based Ionic Liquid

The application of [C₁₂mim]Br ionic liquid/o‐xylene temperature‐dependent biphasic system into the [Imim‐TEMPO][Cl]/O₂‐promoted condensation between o‐phenylenediamines, o‐aminophenol or o‐aminothiophenol with aldehydes for preparing benzimidazoles, benzoxazoles or benzothiozoles is described. Several aldehydes and o‐phenylenediamines, o‐aminophenol or o‐aminothiophenol were reacted efficiently to form corresponding products in excellent yields. Both the [Imim‐TEMPO][Cl] and [C₁₂mim]Br could be reused at least eight times without significantly decreasing the catalytic activity.     

Bicyclic imidazolium-based ionic liquids: synthesis and characterization

We previously reported the use of imidazole as starting compound for preparing a bicyclic imidazolium ionic liquid, [b-3C-im][NTf₂], with an overall 29% isolated yield in four synthetic steps. This new room temperature ionic liquid was shown to be far more chemically stable than commonly used [bmim][PF₆], [bdmim][PF₆], and [bdmim][NTf₂]. Because of this intriguing chemical stability, it prompted us to develop a more generalized and high yielding synthesis so that molecular diversity of bicyclic ionic liquids may be explored. In this work, we amended the previous synthetic route by employing 4-chlorobutyronitrile or 5-chlorovaleronitrile as starting materials and successfully developed a five-step synthesis of a series of novel bicyclic imidazolium-based ionic liquids in 40-53% overall isolated yields. We investigated intrinsic reactivity of all bicyclic ionic liquids prepared and found that, under strongly basic conditions, among all tested ionic liquids the 5,5-membered [R-3C-im][NTf₂] ionic liquids were most stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf₂] ionic liquid was 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. Under identical condition, the commonly used [bmim][NTf₂] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases, only [bmim][PF₆] was deuterium exchanged (50% within 1 h) and all other ionic liquids gave no detectable exchanges even after 25 days at ambient temperature. Moreover, both [bmim][NTf₂] and [bdmim][NTf₂] ionic liquids were readily methylated at C-2 position with methyl iodide under basic condition at room temperature. Under the same condition, [R-3C-im][NTf₂] and [R-4C-im][NTf₂] ionic liquids were completely stable and chemically inert. We envisioned that [R-3C-im][NTf₂] should be well suited as solvents for organic synthesis.     

Effect of additives on the surface active and morphological features of 1-octyl-3-methylimidazolium halide aggregates in aqueous media

The influence of two salts as additives namely sodium chloride and sodium sulphate and a nonelectrolyte, 2-butoxyethanol on surface chemical and aggregation characteristics of ionic liquids (IL) of 1-octyl-3-methylimidazolium chloride, [C₈mim][Cl], 1-octyl-3-methylimidazolium bromide, [C₈mim][Br], and 1-octyl-3-methylimidazolium iodide, [C₈mim][I] in aqueous media were monitored through surface tension and small angle neutron scattering measurements. The addition of salts drastically decreased the critical aggregation concentration (CAC) and increased the area per adsorbed IL molecule. The co-ions of salts modify the surface of IL molecules and aggregates through various interactions such as charge neutralization, specific interactions and dehydration The results obtained by analyzing the SANS curves in the whole Q range showed that the oblate ellipsoidal shape of the aggregates of ionic liquids is un-altered upon the addition of additives. However the additives facilitate the growth of the aggregates in to microstructures with cubic packing at high salt concentrations.     

Effect of imidazolium-based ionic liquids on the aggregation behavior of twin-tailed cationic gemini surfactant in aqueous solution

Micellization behavior of the twin-tailed surfactants can be modulated by the addition of various modifiers. Ionic liquids (ILs) are one of them and are documented here. The beauty of these environmentally benign neoteric molecules lies in their structural versatility. Here, we have investigated the effect of three ILs: 1-butyl-3-methylimidazolium bromide ([C₄mim][Br]), 1-hexyl-3-methylimidazolium bromide ([C₆mim][Br]), and 1-octyl-3-methylimidazolium bromide ([C₈mim][Br]) on the aggregation and surface adsorption behavior of cationic gemini surfactant, bis(hexadecyldimethyl ammonium)propane dibromide (16-3-16) through experimentally measured electrical conductivities, surface tensions, and by spectral methods (UV-vis absorbance and fluorescence measurements). The main focus of the study is to observe the effect of added ILs on the critical micelle concentration (cmc), various surface parameters, aggregation number, and size of the aggregates of gemini surfactant. The results show that the more hydrophobic ILs, that is, [C₆mim][Br] and [C₈mim][Br] behave as electrolyte at lower concentration and cosurfactant at higher concentration, whereas moderately hydrophobic IL [C₄mim][Br] acts as an electrolyte at all concentration ranges studied. The modulating effects of ILs were also compared with conventional electrolyte (NaBr) at similar conditions.     

Ultrafast FRET to Study Spontaneous Micelle‐to‐Vesicle Transitions in an Aqueous Mixed Surface‐Active Ionic‐Liquid System

The spontaneous micelle‐to‐vesicle transition in an aqueous mixture of two surface‐active ionic liquids (SAILs), namely, 1‐butyl‐3‐methylimidazolium n‐octylsulfate ([C₄mim][C₈SO₄]) and 1‐dodecyl‐3‐methylimidazoium chloride ([C₁₂mim]Cl) is described. In addition to detailed structural characterization obtained by using dynamic light scattering, transmission electron microscopy (TEM), and cryogenic TEM techniques, ultrafast fluorescence resonance energy transfer (FRET) from coumarin 153 (C153) as a donor (D) to rhodamine 6G (R6G) as an acceptor (A) is also used to study micelle–vesicle transitions in the present system. Structural transitions of SAIL micelles ([C₄mim][C₈SO₄] or [C₁₂mim]Cl micelles) to mixed SAIL vesicles resulted in significantly increased D –A distances, and therefore, increased timescale of FRET. In [C₄mim][C₈SO₄] micelles, FRET between C153 and R6G occurs on an ultrafast timescale of 3.3 ps, which corresponds to a D –A distance of about 15 Å. As [C₄mim][C₈SO₄] micelles are transformed into mixed micelles upon the addition of a 0.25 molar fraction of [C₁₂mim]Cl, the timescale of FRET increases to 300 ps, which suggests an increase in the D –A distance to 31 Å. At a 0.5 molar fraction of [C₁₂mim]Cl, unilamellar vesicles are formed in which FRET occurs on multiple timescales of about 250 and 2100 ps, which correspond to D –A distances of 33 and 47 Å. Although in micelles and mixed micelles the obtained D –A distances are well correlated with their radius, in vesicles the obtained D –A distance is within the range of the bilayer thickness.