Solvation and Rotation Dynamics in the Trihexyl(tetradecyl)phosphonium Chloride Ionic Liquid/Methanol Cosolvent System

Barra, Kathleen M.; Sabatini, Randy P.; McAtee, Zachery P.; Heitz, Mark P.

doi:10.1021/jp5092784

Cited by 23 publications

(30 citation statements)

References 100 publications

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“…Ionic liquids are often reported to contain a small fluorescence background, and our previous work with [P 6,6,6,14 ] + Cl − is consistent with that observation [22,59,66], showing a broad, featureless emission spectrum with ν pk em = 479 nm [59]. Excitation and emission scans of neat CO 2 showed that it was free from any fluorescent impurities, however, there was measurable pressure-dependent emission when [P 6,6,6,14 ] + Cl − was added to CO 2 .…”

Section: Steady-state Spectroscopysupporting

confidence: 82%

“…The instrument was calibrated using the water Raman signal and all spectra were blank subtracted and corrected for instrument response. Time-resolved emission intensity decays were measured using the Fluorolog-3 instrument, modified with time-correlated single photon counting (TCSPC) components from Horiba Scientific as described elsewhere [59]. In this work, all time-resolved measurements were excited with a 405 nm NanoLED (405-L) high output diode laser operating at a 1 MHz repetition rate, controlled through a FluoroHub controller that was run by DataStation (2.6) software.…”

Section: Methodsmentioning

confidence: 99%

“…More recently, we presented the C153 spectroscopy in binary solutions of [P 6,6,6,14 ] + Cl − /MeOH [59]. Variation of x IL from 0 to 1 allowed us to examine the C153 response to the varying cosolvent microenvironment formed between MeOH and [P 6,6,6,14 ] + Cl − .…”

Section: Steady-state Spectroscopymentioning

confidence: 99%

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Dissolution of Trihexyltetradecylphosphonium Chloride in Supercritical CO2

2017

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Abstract:We present steady-state and time-resolved fluorescence spectroscopic data derived from coumarin 153 (C153) in a binary solution comprised of trihexyltetradecylphosphonium chloride ([P 6,6,6,14 ] + Cl − ) and supercritical CO 2 (scCO 2 ). Steady-state fluorescence of C153 was measured in neat scCO 2 and ionic liquid (IL)-modified scCO 2 solutions. The steady-state excitation and emission peak frequency data in neat scCO 2 and IL/scCO 2 diverge at low fluid density (ρ r = ρ/ρ c < 1). The prominent spectral differences at low fluid density provided clear evidence that C153 reports different microenvironments, and suggested that the IL is solubilized in the bulk scCO 2 and heterogeneity of the C153 microenvironment is readily controlled by scCO 2 density. C153 dimers have been reported in the literature, and this formed the basis of the hypothesis that dimerization is occurring in scCO 2 . Time-dependent density functional theory (TD-DFT) electronic structure calculations yielded transition energies that were consistent with excitation spectra and provided supporting evidence for the dimer hypothesis. Time-resolved fluorescence measurements yielded triple exponential decays with time constants that further supported dimer formation. The associated fractional contributions showed that the dominant contribution to the intensity decay was from C153 monomers, and that in high density scCO 2 there was minimal contribution from C153 dimers.

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Section: Steady-state Spectroscopysupporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

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Dissolution of Trihexyltetradecylphosphonium Chloride in Supercritical CO2

2017

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“…For time-dependent emission, our instrument was modified to include time-correlated single photon counting (TCSPC) components, which has been previously discussed [57,72]. For these experiments, all time-resolved decay measurements were excited using a 405 nm diode laser, high output NanoLED, from Horiba.…”

Section: Methodsmentioning

confidence: 99%

Spectroscopic Studies of a Phosphonium Ionic Liquid in Supercritical CO2

2020

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Fluorescence spectroscopy was used to study a solution comprised of coumarin 153 (C153)+ trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P6,6,6,14]+ [Tf2N]−)+ supercritical CO2 (scCO2). We compare the spectroscopy of C153 in neat scCO2 to that of C153/scCO2 with the addition of ionic liquid (IL). Excitation and emission peak frequencies of C153 in scCO2 and in IL/scCO2 diverged at reduced densities (ρr = ρ/ρc) below the CO2 critical density. At low fluid density, spectral changes in the IL/scCO2 solutions showed evidence that C153 experiences a very different microenvironment—one that is unlike neat scCO2. The data show that the presence of IL clearly influences the C153 excitation and emission profiles. Excitation was broadened and red shifted by >2000 cm−1 and the presence of an additional low-energy emission component that was red shifted by ~3000 cm−1 was clearly visible and not observed in neat scCO2. The solution heterogeneity was controlled by changing the scCO2 density and at high fluid density, both the excitation and emission spectra were more similar to those in neat scCO2. Steady-state anisotropy also showed that at low fluid density, the C153 emission was significantly polarized. Aggregation of C153 has been reported in the literature and this led us to hypothesize the possibility that C153 dimer (aggregation) formation may be occurring in scCO2. Another possible explanation is that dye–IL aggregates may dissolve into the scCO2 phase due to C153 acting as a “co-solvent” for the IL. Time-resolved intensity decay measurements yielded only slightly non-exponential decays with accompanying time constants of ~3–4 ns that were significantly shorter than the 5–6 ns time constants in neat scCO2, which are suggestive of C153–IL interactions. However, these data did not conclusively support dimer formation. Pre-exponential factors of the time constants showed that almost all of the emission was due to monomeric C153.

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“…A non-linear dependence of viscosity on mole fraction was observed below X IL o0.1 while the data vary linearly with mole fraction for X IL 40.1. 156 Studies on mutual miscibility of tetrafluoroborate PILs with common solvents, such as cyclic hydrocarbons 157 and diols 158 were also reported. Mixtures of immiscible ionic liquids including PILs were investigated by Palomar and co-workers, 159 demonstrating the potential of biphasic IL mixtures for extraction/ separation procedures.…”

Section: Preparation and Characterisationmentioning

confidence: 99%