Ultrafast Dynamics in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: A Femtosecond Raman-Induced Kerr Effect Spectroscopic Study

Fukazawa, Hiroki; Ishida, Tateki; Shirota, Hideaki

doi:10.1021/jp200370f

Cited by 49 publications

(76 citation statements)

References 94 publications

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“…In fact, a strong intramolecular vibrational band at about 120 cm −1 has been observed in the Kerr spectra of not only aromatic and nonaromatic cation based ILs with [NTf 2 ] − but also solutions including lithium bis(trifluoromethylsulfonyl)amide. 72 This sharp peak frequency is consistent with the reported quantum chemical calculation results 36 of the anion which showed the frequency modes with relatively large Raman activity of 105.31 cm −1 with B3LYP/aug-cc-pVDZ 59−62,73 level of theory and 105 cm −1 with B3LYP/6-31+G(d, p), 69 respectively. Therefore, this sharp peak is considered to be an intermolecular motion coupled to the vibrational mode intrinsic to the anion.…”

Section: Resultssupporting

confidence: 88%

Dicationic versus Monocationic Ionic Liquids: Distinctive Ionic Dynamics and Dynamical Heterogeneity

Ishida

Shirota

2013

J. Phys. Chem. B

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The dynamical properties of a dicationic ionic liquid (IL), 1,6-bis(3-methylimidazolium-1-yl)hexane bis(trifluoromethylsulfonyl)amide ([C(6)(MIm)(2)][NTf(2)](2)), compared to 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide ([C(3)MIm][NTf(2)]), as its monocationic imidazolic counterpart, are studied by molecular dynamics simulations. We investigate relaxation processes of the polarizability anisotropy of the system and collective dynamics of both the ILs with mean-squared displacement (MSD), non-Gaussian parameter, and the intermediate scattering functions. The analyses of librational dynamics show that the difference of the Kerr spectra between the ILs could be mainly ascribed to the distinctive angular momentum of [C(6)(MIm)(2)](2+) and [C(3)MIm](+) and related to the difference of relaxation behavior between [C(6)(MIm)(2)](2+) and [C(3)MIm](+). Also, it is indicated that the librational dynamics of [NTf(2)](-) indicate a common resonance-type sharp peak that corresponds to an intermolecular motion coupled to the vibrational mode intrinsic to [NTf(2)](-). In addition, it is exhibited from the total X-ray structure factors calculated for both of the ILs that the low-k peak at 0.20 Å(-1) appears for [C(6)(MIm)(2)][NTf(2)](2), while we do not see it for [C(3)MIm][NTf(2)]. We find that the contribution of the anion-cation and anion-anion correlations to the low-k peak is more significant than the cation-cation correlation. Therefore, it is suggested for [C(6)(MIm)(2)][NTf(2)](2) that dynamical heterogeneous behavior strongly correlates with structural variations or heterogeneity.

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Section: Resultssupporting

confidence: 88%

Dicationic versus Monocationic Ionic Liquids: Distinctive Ionic Dynamics and Dynamical Heterogeneity

Ishida

Shirota

2013

J. Phys. Chem. B

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“…Thus, it is rather natural to think that the anion-related motions become more active at higher temperatures. On the other hand, in the 50−100 cm −1 region, which is assigned to the major contribution of the imidazolium ring libration, 22,26,33,66 the spectral density shifts to the lower-frequency side, and its intensity increases as the temperature rises. Next, we further discuss this spectral feature based on the results of line-shape analysis.…”

Section: Articlementioning

confidence: 99%

Temperature Dependence of Low-Frequency Spectra in Molten Bis(trifluoromethylsulfonyl)amide Salts of Imidazolium Cations Studied by Femtosecond Raman-Induced Kerr Effect Spectroscopy

Shirota

Kakinuma

2015

J. Phys. Chem. B

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In this study, the temperature dependence of the low-frequency spectra of liquid bis(trifluoromethylsulfonyl)amide salts of the monocations 1-methyl-3-propylimidazolium and 1-hexyl-3-methylimidazolium and the dications 1,6-bis(3-methylimidazolium-1-yl)hexane and 1,12-bis(3-methylimidazolium-1-yl)dodecane has been investigated by means of femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The intensity in the low-frequency region below 20 cm(-1) in the spectra of the four ionic liquids increases with rising temperature. From a line-shape analysis of the broadened low-frequency spectra of the ionic liquids, it is clear that the lowest-frequency component, which peaks at approximately 5 cm(-1), contributes to the temperature dependence of the spectra. This implies that the activity of the intermolecular translational vibrational motion is increasing with rising temperature. It is also possible that decoupling in the crossover process between intermolecular vibrational motion and structural relaxation occurs as a result of a deterioration of the non-Markovian feature or the loss of memory caused by the higher temperature. The peak of the highest-frequency component, which is due mainly to the imidazolium ring libration, shifts to lower frequency with increasing temperature. This is attributed to weaker interactions of the ionic liquids at higher temperatures. Temperature-dependent viscosities from 293 to 353 K of the four ionic liquids have also been characterized.

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“…Motivated by both the technological applications and the fundamental scientific issues, a growing literature on structure and dynamics of ionic liquids has become available in the last decade using different spectroscopic techniques. 5,[10][11][12][13][14][15][16][17][18] In the low-frequency range, ionic liquids dynamics have been investigated by optical Kerr effect (OKE), [10][11][12][13][14][15] far-infrared, 16,17 terahertz time domain, 16,18 dielectric relaxation, 13,14 and Raman spectroscopies. 16 OKE spectroscopy has been the most commonly used technique for unraveling the intermolecular vibrational dynamics of ionic liquids within the THz range.…”

Section: Introductionmentioning

confidence: 99%

Pressure and temperature effects on intermolecular vibrational dynamics of ionic liquids

Penna

Faria

Matos

et al. 2013

The Journal of Chemical Physics

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Low frequency Raman spectra of ionic liquids have been obtained as a function of pressure up to ca. 4.0 GPa at room temperature and as a function of temperature along the supercooled liquid and glassy state at atmospheric pressure. Intermolecular vibrations are observed at ~20, ~70, and ~100 cm(-1) at room temperature in ionic liquids based on 1-alkyl-3-methylimidazolium cations. The component at ~100 cm(-1) is assigned to librational motion of the imidazolium ring because it is absent in non-aromatic ionic liquids. There is a correspondence between the position of intermolecular vibrational modes in the normal liquid state and the spectral features that the Raman spectra exhibit after partial crystallization of samples at low temperatures or high pressures. The pressure-induced frequency shift of the librational mode is larger than the other two components that exhibit similar frequency shifts. The lowest frequency vibration observed in a glassy state corresponds to the boson peak observed in light and neutron scattering spectra of glass-formers. The frequency of the boson peak is not dependent on the length scale of polar∕non-polar heterogeneity of ionic liquids, it depends instead on the strength of anion-cation interaction. As long as the boson peak is assigned to a mixing between localized modes and transverse acoustic excitations of high wavevectors, it is proposed that the other component observed in Raman spectra of ionic liquids has a partial character of longitudinal acoustic excitations.

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Ultrafast Dynamics in 1-Butyl-3-methylimidazolium-Based Ionic Liquids: A Femtosecond Raman-Induced Kerr Effect Spectroscopic Study

Cited by 49 publications

References 94 publications

Dicationic versus Monocationic Ionic Liquids: Distinctive Ionic Dynamics and Dynamical Heterogeneity

Dicationic versus Monocationic Ionic Liquids: Distinctive Ionic Dynamics and Dynamical Heterogeneity

Temperature Dependence of Low-Frequency Spectra in Molten Bis(trifluoromethylsulfonyl)amide Salts of Imidazolium Cations Studied by Femtosecond Raman-Induced Kerr Effect Spectroscopy

Pressure and temperature effects on intermolecular vibrational dynamics of ionic liquids

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