城田 秀明

The microscopic aspects of 1-methyl-3-octylimida-zolium tetrafluoroborate ([MOIm][BF4]) mixtures with forma-mide (FA), N-methylformamide (NMF), and N,N-dimethylforma-mide (DMF) were investigated using spectroscopic techniques of femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES), FT-IR, and NMR. Molecular dynamics simulations and quantum chemistry calculations were also performed. According to fs-RIKES, the first moment of the low-frequency spectrum bands mainly originating from the intermolecular vibrations in the [MOIm]-[BF4]/FA and [MOIm][BF4]/DMF systems changed gradually with the molecular liquid mole fraction XML but that in the [MOIm][BF4]/NMF system was constant up to XNMF = 0.7 and then gradually increased in the range of XNMF > 0.7. Excluding the contribution of the 2D hydrogen-bonding network due to the presence of FA in the low-frequency spectrum band, the XML dependence of the normalized first moment of the low-frequency band in the [MOIm][BF4]/FA and [MOIm][BF4]/NMF systems revealed that the normalized first moment did not remarkably change in the range of XML < 0.7 but drastically increased in XML > 0.7. FT-IR results indicated that the amide C=O band shifted to the low-frequency side with increasing XML for the three mixtures due to the hydrogen bonds. The imidazolium ring C-H band also showed a similar tendency to the amide C=O band. 19F NMR probed the microenvironment of [BF4]- in the mixtures. The [MOIm][BF4]/NMF and [MOIm][BF4]/DMF systems showed an up-field shift of the F atoms of the anion with increasing XML, and the [MOIm][BF4]/FA system exhibited a down-field shift. Steep changes in the chemical shifts were confirmed in the region of XML > 0.8. On the basis of the quantum chemistry calculations, the observed chemical shifts with increasing XML were mainly attributed to the many-body interactions of ions and amides for the [MOIm][BF4]/FA and [MOIm][BF4]/DMF systems. Meanwhile, the long distance between the cation and the anion was due to the high dielectric medium for the [MOIm][BF4]/NMF system, which led to an up-field shift.

In this study, we investigated the low-frequency spectra below 650 cm(-1) of aqueous reline solutions with various concentrations via femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and molecular dynamics (MD) simulations. The density, surface tension, viscosity, and electrical conductivity of the aqueous reline solutions were also measured. In the low-frequency spectrum, the peak frequency due to intermolecular vibrations of the aqueous reline solutions proportionally shifted to lower frequency with increasing the water content (C-H2O; wt%). The density of state (DOS) spectra of aqueous reline solutions obtained via MD simulations also showed a red shift of the low-frequency spectrum upon increasing C-H2O. A decomposition analysis of the DOS spectra revealed that the peaks corresponding to all components, that is, choline cation, urea, chloride, and water, showed a lower frequency shift in the DOS spectrum with increasing C-H2O. The plot of the peak frequency of the low-frequency spectrum vs the bulk parameter root gamma/rho (gamma: surface tension; rho: density) in aqueous reline solutions showed two relations at a turning point C-H2O = 10 wt%, which can be attributed to a change in the microscopic structure of the aqueous reline solution from a bulk-like reline structure to reline clusters.

In the present study, we demonstrate the facile preparation of deep eutectic solvents (DESs) composed of various imidazolium iodides and iodine. The electrical conductivity of the DESs was high and was control-lable by changing the composition of the mixtures and the imidazolium cation species. In particular, the DES composed of 1-ethyl-3-methylimidazolium iodide and iodine in a 1:4 molar ratio showed an electri-cal conductivity as high as 70 mS cm-1, which was higher than that of ionic liquid (1-butyl-3-methylimidazolium iodide and 1-hexyl-3-methylimidazolium iodide) mixtures with iodine. The electri-cal conductivity of DESs based on 1-alkyl-3-methylimidazolium iodides increased with increasing iodine content. The high electrical conductivity of DESs was attributed to the Grotthuss mechanism in polyio-dide based on the viscosity results, Raman spectrum measurements, and quantum chemistry calculations.(c) 2022 Elsevier B.V. All rights reserved.

This study compared the physical properties, e.g., glass transition temperature, melting point, viscosity, density, surface tension, and electrical conductivity, and the low-frequency spectra under 200 cm-1 of three synthesized ionic liquids (ILs), triethylpentylphosphonium bis(fluorosulfonyl)amide ([P2225][NF2]), ethoxyethyltriethylphosphonium bis(fluorosulfonyl)amide ([P222(2O2)][NF2]), and triethyl[2-(ethylthio)ethyl]phosphonium bis(fluorosulfonyl)amide ([P222(2S2)][NF2]), at various temperatures using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and terahertz time-domain spectroscopy (THzTDS). The [P222(2S2)][NF2] had the highest viscosity and glass transition temperature, whereas the [P222(2O2)][NF2] had the lowest. Among the three ILs, the [P222(2S2)][NF2] had the highest density and surface tension, and the [P222(2O2)][NF2] had the highest electrical conductivity. The RIKES and THz-TDS spectral line shapes for the three ILs varied significantly. For the [P2225][NF2], molecular dynamics simulations successfully reproduced the line shapes of the experimental spectra and indicated that the RIKES spectrum was mainly due to the cation and cross-term and their rotational motions, whereas the THz-TDS spectrum was mainly due to the anion and its translational motion. This shows that it is desirable to utilize both fs-RIKES and THz-TDS methods to reveal molecular motions at the low-frequency domain. The [P222(2S2)][NF2] had higher frequency peaks and broader bands in the low-frequency spectra via fs-RIKES and THz-TDS than those for the [P2225][NF2] and [P222(2O2)][NF2].

In this study, we investigated the temperature dependence Negatively Charged of intermolecular vibrations and orientational dynamics in the aqueous solutions of imidazole hydrochloride, imidazole, sodium triazolide, and triazole using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and steady-state Raman spectroscopy. The difference low-frequency Raman spectra under 250 cm(-1 )of the aqueous solutions relative to the neat water showed that the spectral shoulder in the high-frequency region at 60-100 cm(-1), assigned to the libration of an aromatic ring, was higher in frequency for the imidazolium cation but lower for the triazolide anion than those of the respective neutral aromatics. The results of the ab initio quantum chemistry calculations of the clusters of the aromatics and water molecule(s) were consistent with the experimental spectra of the aqueous solutions. Further, the results of the temperature-dependent experiments showed that the signal intensity in the low-frequency region below 50 cm(-1) increased for all solutions with an increase in temperature. In contrast, the spectral density in the high-frequency region above 80 cm(-1) exhibited almost no shift for the 1.0 M solutions, while a significant red shift was observed for the 5.0 M solutions. In addition, the temperature-dependent densities, viscosities, and surface tensions were characterized for the aqueous aromatic solutions from 293 to 353 K.

We investigated the intermolecular dynamics and static structure in the aqueous solutions of lidocaine hydrochloride (LDHCl) in the concentration range of [LDHCl] = 0-2.00 M using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES), small- and wide-angle X-ray scattering (SWAXS), and dynamic light scattering (DLS). For the fs-RIKES experiments, the concentration dependence of the difference low-frequency spectra of the aqueous LDHCl solutions relative to the neat water, which was mainly due to the intermolecular vibrations, was characterized using an exponential function with a characteristic concentration of similar to 1 M. For the SWAXS experiments, we observed a manifestation of an excess scattering component centered within a range of 8-10 nm(-1) in the aqueous LDHCl solutions. The results of Fourier inversion and further deconvolution analyses unambiguously demonstrated that lidocaines assemble into a nanometer-sized micelle-like structure with the innermost core (similar to 0.3 nm) and outer shell (similar to 0.5 nm), respectively. The DLS experiments also found nanometer-sized aggregates and further indicated evidence of the clusters of the aggregates. The results of viscosities, densities, and surface tensions of the solutions and the quantum chemistry calculations supported the unique features of the microscopic intermolecular interaction and the micelle-like aggregation.

The mixing states of two imidazolium-based ionic liquids (ILs) with different anions, 1-methyl-3-octylimidazolium tetrafluoroborate (C(8)mimBF(4)) and bis(trifluoromethylsulfonyl)amide (C(8)mimTFSA), with three molecular liquids (MLs), methanol (MeOH), acetonitrile (AN), and dimethyl sulfoxide (DMSO), have been investigated on both mesoscopic and microscopic scales using small-angle neutron scattering (SANS), infrared (IR), and H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy. Additionally, molecular dynamics (MD) simulations have been conducted on the six combinations of ILs and MLs to observe the states of their mixtures on the atomic level. The SANS profiles of the IL-ML mixtures suggested that MeOH molecules only form clusters in both C(8)mimBF(4) and C(8)mimTFSA, whereas AN and DMSO were homogeneously mixed with ILs on the SANS scale. MeOH clusters are more enhanced in BF4--IL than TFSA(-)-IL. The microscopic interactions among IL cations, anions, and MLs should contribute to the mesoscopic mixing states of the IL-ML mixtures. In fact, the IL cation-anion, cation-ML, anion-ML, and ML-ML interactions observed by IR, NMR, and MD simulations clarified the reasons for the mixing states of the IL-ML binary solutions observed by the SANS experiments. In neat ILs, the imidazolium ring of the IL cation more strongly interacts with TFSA(-)than TFSA(-) due to the higher charge density of the former. The interaction of anions with the imidazolium ring is more easily loosened on adding MLs to ILs in the order of DMSO > MeOH > AN. It does not significantly depend on the anions. However, the replacement of the anion on the imidazolium ring by an ML depends on the anions; the replacement is more proceeded in the order of MeOH > DMSO > AN in BF4--IL, while DMSO > MeOH > AN in TFSA(-)-IL. On the other hand, the solvation of both anions by MLs is stronger in the order of MeOH > DMSO approximate to AN. Despite the stronger interactions of MeOH with both cations and anions, MeOH molecules are heterogeneously mixed with both Its to form clusters in the mixtures. Therefore, the self-hydrogen bonding among MeOH molecules most markedly governs the mixing state of the binary solutions among the abovementioned interactions.

This is the first report on low-frequency spectra of ionic liquid (IL)/polymer mixtures using femtosecond Raman-induced Kerr effect spectroscopy. We studied mixtures of 1-methyl-3-octylimidazolium tetrafluoroborate ([MOIm][BF4]) and poly(ethylene glycol) (PEG) with M-n = 400 (PEG400) at various concentrations. To elucidate the unique features of the IL/polymer mixture system, mixtures of PEG400 with a molecular liquid, 1-octhylimidazole (OIm), which is a neutral analog of the cation, were also studied. In addition, mixtures of [MOIm][BF4] with ethylene glycol (EG) and poly(ethylene glycol) with M-n = 4000 (PEG4000) were also investigated. The first moments of broad low-frequency spectra, mainly due to intermolecular vibrations for the [MOIm][BF4]/PEG400 and OIm/PEG400, increased slightly with increasing concentration of PEG400, indicating that microscopic intermolecular interactions, in general, are slightly enhanced. We also compared the [MOIm][BF4] mixtures with EG, PEG400, and PEG4000 at concentrations of 5 and 10 wt % PEG or EG. The low-frequency spectra of samples with the same concentrations were quite similar, but a comparison of the normalized spectra showed that the spectral intensity in the low-frequency region below similar to 50 cm(-1) of the [MOIm][BF4] mixtures with PEG400 and PEG4000 is somewhat lower than that of the [MOIm][BF4] mixtures with EG. Although the effect of the polymer is small compared to other polymer solution systems, this feature is attributed to a suppression of translational motion in the mixtures of [MOIm][BF4] with PEG compared to the mixtures of [MOIm][BF4] with EG due to the greater mass of PEG than EG. Density, surface tension, viscosity, and electrical conductivity were also estimated. From Walden plots, it was found that the [MOIm][BF4]/PEG4000 system showed more ideal electrical conductive behavior than the [MOIm][BF4]/PEG400 and [MOIm][BF4]/EG systems.

In this study, we examined the low-frequency spectra of 1-methyl-3-octylimidazolium tetrafluoroborate ([MOIm][BF4]) mixtures with methanol (MeOH), acetonitrile (MeCN), and dimethyl sulfoxide (DMSO), which were obtained by femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and molecular dynamics (MD) simulations. In addition, we estimated the liquid properties of the mixtures, such as density ρ, surface tension γ, viscosity η, and electrical conductivity σ. The line shapes of the low-frequency Kerr spectra of the three [MOIm][BF4] mixture systems strongly depend on the mole fraction of the molecular liquid, XML. The spectral intensity increases with increasing XML of the [MOIm][BF4]/MeCN system but decreases for the [MOIm][BF4]/MeOH and [MOIm][BF4]/DMSO systems. These behaviors of the spectral intensities reasonably agree with the vibrational density-of-states spectra when the polarizability anisotropies of MeOH, MeCN, DMSO, and ion species are considered. The characteristic frequencies (first moments, M1) of the low-frequency spectra of the three mixture systems are almost insensitive at XML = 0-0.6. However, the frequencies vary mildly at XML = 0.6-0.9 and dramatically at XML = 0.9-1. The XML-dependent M1 in the Kerr spectra are well reproduced by the MD simulations. Plots of M1 versus bulk parameter, (γ/ρ)1/2, for the three mixture systems show that the mixtures at XML = 0-0.6 behave like aromatic cation-based ionic liquids (ILs), those at XML = 0.9-1 are molecular liquids (MLs), and those at XML = 0.6-0.9 are transitioning between aromatic cation-based ILs and MLs. MD simulations show that the solvent molecules localized at the interface between the ionic and the alkyl group regions without forming large solvent networks at XML = 0-0.6. However, solvent networks or regions develop largely at XML = 0.6-0.9 and the constituent ions of the IL disperse in the MLs at XML = 0.9-1. The MD simulations corroborate the results obtained by fs-RIKES.

In this study, the low-frequency vibrational dynamics of polystyrene (PS) in CCl was investigated by femtosecond Raman-induced Kerr effect spectroscopy. Ethylbenzene (EBz) was also investigated as a model monomer of the polymer to elucidate the unique dynamical features of PS in solution. The broadened low-frequency spectrum of the PS/CCl in the frequency region below 150 cm is significantly different from that of the EBz/CCl . Difference spectra between the PS or EBz solutions and neat CCl , normalized to an internal vibrational mode of CCl , clearly show a much lower spectral intensity for the PS/CCl than the EBz/CCl in the low-frequency region below ca. 20 cm . This indicates that translational motions are suppressed in the PS/CCl compared to the EBz/CCl . Moreover, the high-frequency motion at ca. 70 cm , mainly due to phenyl ring librations, occurs at higher frequency in PS (78 cm ) than EBz (65 cm ). In addition, the results of concentration-dependent experiments show that the first moment (M ) of the low-frequency difference spectra of both PS/CCl and EBz/CCl is almost independent of the concentration. The molecular weight dependence of the low-frequency spectrum in the PS/CCl shows that the M value of the low-frequency spectral band of PS shifts to higher frequencies when the molecular weight of PS increases up to M = &tild;1000, which corresponds approximately to the decamer, and then remains constant upon further increasing the molecular weight. 4 4 4 4 4 4 4 4 4 1 4 4 4 1 w -1 -1 -1 -1 -1

Herein, the data of the intermolecular vibrations of forty nonaromatic cation based ionic liquids (ILs) at 293 K measured by femtosecond Raman-induced Kerr effect spectroscopy are reported. The low-frequency spectra in the frequency range of 0.3700 cm were obtained by Fourier transform deconvolution analysis. The line shapes of the low-frequency spectra below 200 cm were discussed on the basis of the ion species. The spectral intensity in nonaromatic cation based ILs was much lower than that in aromatic cation based ILs owing to the absence of the aromatic ring, i.e., the libration of the aromatic species had a strong spectral intensity in the low-frequency region. However, nonaromatic cation based ILs with a flat anion, such as dicyanamide and tricyanomethanide, showed stronger spectral intensity because of the libration of the anion. Other unique spectral features were also discussed in the context of the structure of the ion species. Liquid properties, such as density, viscosity, electrical conductivity, and surface tension, were also estimated. On comparing the low-frequency spectra with the bulk liquid properties of the nonaromatic cation based ILs, a mild linear relationship between the first moment of the low-frequency spectrum and a bulk parameter comprised of surface tension and density was observed. 11 3 11

Herein, we report the liquid properties, that is, densities, viscosities, electrical conductivities, surface tensions, melting points, and glass transition temperatures, of 18 novel sulfur-containing phosphonium cation-(triethyl[(methylthio)methyl]phosphonium, triethyl[2-(methylthio)ethyl]phosphonium, triethyl[2-(ethylthio)ethyl]phosphonium, tributyl[(methylthio)methyl]phosphonium, tributyl[2-(methylthio)ethyl]phosphonium, tributyl[2-(ethylthio)ethyl]phosphonium) based ionic liquids with bis(trifluoromethylsulfonyl)amide, bis(fluorosulfonyl)amide, and tetrafluoroborate anions. The effects of the (alkylthio)alkyl groups on the viscosity and surface tension of the ionic liquids are very different from those of common alkyl groups in typical ionic liquids.

We investigated the temperature dependence of the intermolecular vibrational dynamics of pyrrolidinium-based ionic liquids (ILs) with 10 different anion species using femtosecond Raman-induced Kerr effect spectroscopy. The features of the temperature-dependent vibrational spectra vary with the different anions. In the case of the ILs with spherical top anions, such as tetrafluoroborate and hexafluorophosphate, and trifluoromethanesulfonate, the spectral intensity in the low-frequency region below 50 cm increases with rising temperature, while that in the high-frequency region above 50 cm remains almost unchanged. Similar temperature-dependent features were also found in the bis(fluorosulfonyl)amide and bis(perfluoroalkylsulfonyl)amide salts. However, the difference spectra at respective temperature relative to 293 K indicate that the spectra of the bis(fluorosulfonyl)amide and bis(perfluoroalkylsulfonyl)amide salts are more temperature-sensitive in the low-frequency region below 50 cm compared to those of the tetrafluoroborate, hexafluorophosphate, and trifluoromethanesulfonate salts. The spectra of 1-butyl-1-methylpyrrolidinium-based ILs with dicyanamide and tricyanomethide anions show a characteristic temperature dependence; in addition to an increase of the spectral intensity in the low-frequency region below 50 cm , a red shift of the spectra in the high-frequency side above 50 cm was observed with increasing temperature. This implies that the librational motions of planar dicyanamide and tricyanomethide anions contribute substantially to the low-frequency spectra. We also compared the temperature-dependent low-frequency spectra of 1-butyl-1-methylpyrrolidinium- and 1-(2-methoxyethyl)-1-methylpyrrolidinium-based ILs with some anions. Although the spectral shapes are slightly different in the range of 70-150 cm , which can be attributed to the intramolecular vibrational modes of the cations, the temperature dependence of the spectral shapes is quite similar, indicating that the ether substitution in the cation side groups has little effects on the temperature dependence of the low-frequency spectra. The fragilities of the ILs were also estimated from the temperature-dependent viscosities and the glass-transition temperatures. The fragility parameter seems to be correlated with the temperature dependence of the first moment of the low-frequency spectral bands mainly arising from the intermolecular vibrations of the ILs. -1 -1 -1 -1 -1 -1

In this study, we have investigated the effects of cation structures on the temperature dependence of the intermolecular vibrational dynamics of ionic liquids using femtosecond Raman-induced Kerr effect spectroscopy. The ionic liquids used in this study are bis(trifluoromethylsulfonyl)amide [NTf ] salts of the cations 1-butyl-3-methylimidazolium [C MIm] , 1-butyl-1-methylpyrrolidinium [Pyrr ] , 1-butylpyridinium [C Py] , butyldiethylmethylammonium [N ] , triethyloctylammonium [N ] , and triethyloctylphosphonium [P ] . All of the ionic liquids show temperature-dependent low-frequency spectra. A difference in the temperature dependence between the spectra of the aromatic and nonaromatic cation based ionic liquids is especially significant. In the case of the aromatic cation based ionic liquids [C MIm][NTf ] and [C Py][NTf ], the spectral intensities in the low-frequency region below ca. 50 cm increase and the high-frequency components at ca. 80 cm shift to lower frequencies with rising temperature. In contrast, the ionic liquids based on nonaromatic cations only exhibit an increase in the low-frequency region below ca. 50 cm with increasing temperature, while the high-frequency region of the spectra above ca. 50 cm shows little change with variation of the temperature. These results suggest that the presence or absence of aromatic rings is the main factor in determining the temperature-dependent spectral features, particularly in the high-frequency region. We also found that the alkyl chain length and central atoms of the nonaromatic quaternary cations do not have much influence on the temperature-dependent spectral features. The first moments of the aromatic cation based ionic liquids are a little more sensitive to temperature than those of the nonaromatic cation based ionic liquids. The temperature-dependent viscosities and fragilities of the ionic liquids have also been examined. 2 4 14 4 1224 2228 2228 4 2 4 2 - + + + + + + -1 -1 -1 -1

In this study, we investigate the temperature dependence of low-frequency spectra in the frequency range of 0.3-200 cm for ionic liquids (ILs) whose cations possess two systematically different cyclic groups, using femtosecond Raman-induced Kerr effect spectroscopy. The target ILs are bis(trifluoromethylsulfonyl)amide [NTf ] salts of 1-cyclohexylmethyl-1-methylpyrrolidinium [CHxmMPyrr] , 1-cyclohexylmethyl-3-methylimidazolium [CHxmMIm] , N-cyclohexylmethylpyridinium [CHxmPy] , 1-benzyl-1-methylpyrrolidinium [BzMPyrr] , 1-benzyl-3-methylimidazolium [BzMIm] , and N-benzylpyridinium [BzPy] cations. The aim of this study is to better understand the effects of aromaticity in the cations' constituent groups on the temperature-dependent low-frequency spectral features of the ILs. The low-frequency spectra of these ILs are temperature dependent, but the temperature-dependent spectrum of [CHxmMPyrr][NTf ] is different from that of other ILs. While [CHxmMPyrr][NTf ] shows spectral changes with temperature in the low-frequency region below 50 cm , the other ILs also show spectral changes in the high-frequency region above 80 cm (above 50 cm in the case of [BzMPyrr][NTf ]). We conclude that the spectral change in the low-frequency region is due to both the cation and anion, while the change in the high-frequency region is attributed to the red shift of the aromatic ring librations. On the basis of the plots of the first moment of the spectra vs. temperature, we found that the first moment of the low-frequency spectrum of the IL whose cation does not have an aromatic ring is less temperature dependent than that of the other ILs. However, the intrinsic first moment, the first moment at 0 K, of the low-frequency spectrum is governed by the absence or presence of a charged aromatic group, while a neutral aromatic group does not have much influence on determining the intrinsic first moment. -1 - + + + + + + -1 -1 -1 2 2 2 2

The temperature dependence of the intermolecular vibrational dynamics in imidazolium-based ionic liquids (ILs) with 10 different anions was studied by femtosecond Raman-induced Kerr effect spectroscopy. For all ILs investigated in this study, the intensity in the low-frequency region below 50 cm increases, and the spectral density in the high-frequency region above 80 cm-1 decreases (and shows a redshift) with increasing temperature. The first phenomenon would be attributed to the activation of the translational vibrational motions, whereas the second one is ascribed to the slowing librational motion of the imidazolium ring with increasing temperature. Calculated spectra of the density of states for the intermolecular vibrations of 1-butyl-3-methylimidazolium hexafluorophosphate, which is one of the experiment samples studied here, obtained by molecular dynamics simulation agreed well with the experimental results and confirmed the spectral assignments. When we compared the difference spectra between spectra measured at various temperatures and the spectrum measured at 293 K, a clear difference was found in the ~50 cm region of the Kerr spectra of 1-butyl-3-methylimidazolium thiocyanate and 1-butyl-3-methylimidazolium dicyanamide from those of the other ILs. The difference might have originated from the librational motions of the corresponding anions. We also compared the temperature-dependent Kerr spectra of hexafluorophosphate salts of 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, and 1-heptyl-3-methylimidazolium cations. These ILs showed a similar temperature dependence, which was not affected by the alkyl group length. The temperature-dependent viscosities and glass transition temperatures of the ILs were also estimated to determine their fragilities. -1 -1

Significantly lower viscosities result when a single alkyl carbon is replaced by a silicon atom on the side chain of an ionic liquid cation. To further explore this effect, we compare liquid structure factors measured using high-energy X-ray scattering and calculated using molecular dynamics simulations. Four ionic liquids are studied that each has a common anion, bis(trifluoromethylsulfonyl)amide (NTf 2 -). The four cations for this series of NTf 2 - -anion ionic liquids are 1-methyl-3-trimethylsilylmethylimidazolium (Si-mim ), 1-methyl-3-neopentylimidazolium (C-mim ), 1-methyl-3-pentamethyldisiloxymethylimidazolium (SiOSi-mim ), and 1-methyl-1-trimethylsilylmethylpyrrolidinium (Si-pyrr ). To achieve quantitative agreement between the structure factors measured using high-energy X-ray scattering and molecular dynamics simulations, new transferable parameters for silicon were calibrated and added to the existing force fields. + + + +

The microscopic aspects of the two series of mixtures of 1-methyl-3-octylimidazolium tetrafluoroborate ([MOIm][BF ])-benzene and 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)amide ([MOIm][NTf ])-benzene were investigated by several spectroscopic techniques such as attenuated total reflectance IR (ATR-IR), NMR, and fs-Raman-induced Kerr effect spectroscopy (fs-RIKES). All three different spectroscopic results indicate that the anions more strongly interact with the cations in the [MOIm][BF ]-benzene mixtures than in the [MOIm][NTf ]-benzene mixtures. This also explains the different miscibility features between the two mixture systems well. The x H dependences of the chemical shifts and the C-H out-of-plane bending mode of benzene are similar: the changes are large in the high benzene concentration (x H > μ0.6) compared to the low benzene concentration. In contrast, the linear x H dependences of the first moments of the low-frequency spectra less than 200 cm were observed in both the [MOIm][BF ]-benzene and [MOIm][NTf ]-benzene systems. The difference in the x H dependent features between the chemical shifts and intramolecular vibrational mode and the intermolecular/interionic vibrational bands might come from the different probing space scales. The traces of the parallel aromatic ring structure and the T-shape structure were found in the ATR-IR and NMR experiments, but fs-RIKES did not observe a clear trace of the local structure. This might imply that the interactions between the imidazolium and benzene rings are not strong enough to librate the imidazolium and benzene rings together. The bulk properties, such as miscibility, density, viscosity, and surface tension, of the two ionic liquid-benzene mixture series were also compared to the microscopic aspects. 4 2 4 2 C6 6 C6 6 C6 6 4 2 C6 6 -1

We studied the ultrafast dynamics of 40 aromatic cation based ionic liquids (ILs) by means of femtosecond Ramaninduced Kerr effect spectroscopy. The low-frequency Kerr spectra (ca. 0.3700 cm1) of the ILs were obtained from the Kerr transients by Fourier-Transform deconvolution analysis. The low-frequency Kerr spectra in the frequency range less than 200 cm coming mainly from the intermolecular vibrations for the ILs were discussed in terms of (i) anion dependence, (ii) imidazolium cations vs. pyridinium cations, (iii) alkyl group dependence, and (iv) effect of methylation in aromatic cations. Several liquid properties, such as density, viscosity, electrical conductivity, and surface tension, of the present sample ILs at 293K were also estimated in this study. We clarified that the aromatic cation based ILs show a different relation of the first moment of the low-frequency spectral band to the bulk liquid parameter, which is the square root of surface tension divided by liquid density, from aprotic molecular liquids. The slope of the first moment to the bulk parameter for the aromatic cation based ILs is gentler than that for aprotic molecular liquids. -1

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.

We have critically investigated the low-frequency spectra of six ionic liquids (ILs) consisting of systematically different cations having benzyl moieties or comparable-sized saturated cyclohexylmethyl groups, by means of femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES). The target ionic liquids are bis(trifluoromethylsulfonyl)amide ([NTf<inf>2</inf>]^-) salts of the 1-benzyl-3-methylimidazolium ([BzMIm]⁺), 1-benzyl-1-methylpyrrolidinium ([BzMPyrr]⁺), 1-benzylpyridinium ([BzPy]⁺), 1-cyclohexylmethyl-3-methylimidazolium ([CHxmMIm]⁺), 1-cyclohexylmethyl-1-methylpyrrolidinium ([CHxmMPyrr]⁺), and 1-cyclohexylmethylpyridinium ([CHxmPy]⁺) cations. The primary purpose of this study is to clarify the effects of charged and neutral aromatic moieties on the low-frequency spectrum and bulk properties such as liquid density, surface tension, shear viscosity, glass transition temperature, and melting point. We found that ILs with benzyl groups have larger surface tensions than those with the same cation bearing the cyclohexylmethyl group. The trend in the glass transition temperatures, comparing ILs having the same side group, is pyridinium > imidazolium > pyrrolidinium. The effects of a single aromatic moiety on the shear viscosity are inconclusive, although the viscosities of the ILs with aromatic moieties on both the cation and the benzyl group, i.e., [BzMIm][NTf<inf>2</inf>] and [BzPy][NTf<inf>2</inf>], are substantially lower than those of the other ILs at room temperature, as a consequence of their higher fragilities. In the low-frequency Kerr spectra in the frequency range of approximately 0.1 to 200 cm^-1 measured by fs-RIKES, the ILs possessing two aromatic groups show the largest relative intensity of the nuclear response to the electronic response. Both the charged and neutral aromatic rings show signals due to the ring libration; the neutral one appears at a lower frequency than the charged one. The relationship between the first moment of the broad low-frequency spectrum band and the bulk parameter consisting of the square root of the surface tension divided by the liquid density is obeyed by the cyclohexylmethyl derivatives whether the cation is aromatic or not, but not by the ILs with the neutral aromatic benzyl group. Quantum chemistry calculations have been also performed to understand the vibrational modes of the ionic species in the ILs. (Graph Presented).

A detailed investigation on the molecular dynamics of ionic deep eutectic solvents (acetamide + lithium nitrate/sodium thiocyanate) is reported. The study was carried out employing dielectric relaxation spectroscopy covering seven decades in frequency (10^-1-10⁶ Hz) and in a wide temperature range from 373 K down to 173 K, accessing the dynamic observables both in liquid and glassy state. The dielectric response of the ionic system has been presented in the dynamic window of modulus formalism to understand the conductivity relaxation and its possible connection to the origin of localized motion. Two secondary relaxation processes appear below glass transition temperature. Our findings provide suitable interpretation on the nature of secondary Johari-Goldstein process describing the ion translation and orientation of dipoles in a combined approach using Ngai's coupling model. A nearly constant loss feature is witnessed at shorter times/lower temperatures. We also discuss the ac conductivity scaling behavior using Summerfield approach and random free energy barrier model which establish the time-temperature superposition principle. These experimental observations have fundamental importance on theoretical elucidation of the conductivity relaxation and glass transition phenomena in molten ionic conductors.

The intermolecular dynamics of five six-membered-ring molecular liquids having different aromaticities - benzene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, cyclohexene, and cyclohexane - measured by femtosecond Raman-induced Kerr effect spectroscopy have been compared in this study. The line shapes of the Fourier transform low-frequency spectra, which arise from the intermolecular vibrational dynamics, are trapezoidal for benzene and 1,3-cyclohexadiene, triangular for 1,4-cyclohexadiene and cyclohexene, and monomodal for cyclohexane. The trapezoidal shapes of the low-frequency spectra of benzene and 1,3-cyclohexadiene are due to the librational motions of their aromatic planar structures, which cause damped nuclear response features. The time integrals of the nuclear responses of the five liquids correlate to the squares of the polarizability anisotropies of the molecules calculated on the basis of density functional theory. The first moments of the low-frequency spectra roughly linearly correlate to the bulk parameters of the square roots of the surface tensions divided by the densities and the square roots of the surface tensions divided by the molecular weights, but the plots for cyclohexene deviate slightly from the correlations. The picosecond overdamped transients of the liquids are well fitted by a biexponential function. The fast time constants of all of the liquids are approximately 1.1-1.4 ps, and they do not obey the Stokes-Einstein-Debye hydrodynamic model. On the other hand, the slow time constants are roughly linearly proportional to the products of the shear viscosities and the molar volumes. The observed intramolecular vibrational modes at less than 700 cm for all of the liquids are also assigned on the basis of quantum chemistry calculations. (Graph Presented). -1

Intermolecular dynamics, particularly intermolecular vibrational dynamics, in simple aprotic molecular liquids including both nonaromatic and aromatic molecular liquids measured using femtosecond Raman-induced Kerr effect spectroscopy is discussed. A correlation between the first moment of the intermolecular vibrational band and the value of the static physical properties, the square root of surface tension divided by liquid density, is shown. The data of the aprotic molecular liquids are also compared to that of room temperature ionic liquids.

In this study, we have investigated the ion concentration dependent collective dynamics in two series of deep eutectic solvent (DES) systems by femtosecond Raman-induced Kerr effect spectroscopy, as well as some physical properties, e.g., shear viscosity (η), density (ρ), and surface tension (γ). The DES systems studied here are [0.75CH CONH + 0.25{f KSCN + (1 - f )NaSCN}] and [0.78CH CONH + 0.22{f LiBr + (1 - f )LiNO }] with f = 0, 0.2, 0.4, 0.6, 0.8, and 1.0. γ of these DES systems shows near insensitivity to f, while ρ shows a moderate dependence on f. Interestingly, η exhibits a strong dependence on f. In the low-frequency Kerr spectra, obtained via the Fourier transform of the collected Kerr transients, a characteristic band at ∼70 cm is clear in [0.78CH CONH + 0.22{f LiBr + (1 - f )LiNO }] DES especially at the larger f. The band is attributed to the intermolecular hydrogen bond of acetamide. Because of less depolarized Raman activities of intermolecular/interionic vibrational motions, which are mostly translational (collision-induced or interaction-induced) motions, of spherical ions, the intermolecular hydrogen-bonding band is clearly observed. In contrast, the intermolecular hydrogen-bonding band is buried in the other intermolecular/interionic vibrational motions, which includes translational and reorientational (librational) motions and their cross-terms, in [0.75CH CONH + 0.25{f KSCN + (1 - f )NaSCN}] system. The first moment (M ) of the intermolecular/interionic vibrational band in these DES systems is much higher than that in typical neutral molecular liquids and shows a weak but contrasting dependence on the bulk parameter γ/ρ. The time constants for picosecond overdamped Kerr transients in both the DES systems, which are obtained on the basis of the analysis fitted by a triexponential function, are rather insensitive to f for both the DES systems, but all the three time constants (fast: ∼1-3 ps; intermediate: ∼7-20 ps; and slow: ∼100 ps) are different between the [0.78CH CONH + 0.22{f LiBr + (1 - f )LiNO }] and [0.75CH CONH + 0.25{f KSCN + (1 - f )NaSCN}] systems. These results indicate that the intermolecular/interionic interactions in DES systems is strongly influenced by the ionic species present in these DES systems. 3 2 3 2 3 3 2 3 3 2 1 3 2 3 3 2 -1

We have investigated 7-azaindole (AI) in a variety of solvents including CCl , CHCl , CH Cl , acetone, CH CN, and DMSO by femtosecond Raman-induced Kerr effect spectroscopy. In differential low-frequency Kerr spectra between the solutions and the respective neat solvents, vibrational bands of the AI hydrogen-bonding (HB) dimer have been observed at ca. 90 and 105 cm in CHCl and CH Cl , as well as CCl : the standard solvent for the AI dimer. In contrast, a broad monomodal band at ca. 80 cm characterizes an HB mode between the AI monomer and solvent in acetone, CH CN, and DMSO. The overdamped Kerr transients in the picosecond region show evidence of both the AI monomer and dimer reorientations in CHCl , CH Cl , acetone, and CH CN, but only the monomer reorientation has been confirmed in DMSO. The clear intermolecular HB bands have not been observed in acetone, CH CN, and DMSO because these solvents are sufficiently strong HB acceptors, which form HB AI-solvent complexes, thus preventing quantitative AI dimerization. In addition, it is plausible that the HB band of between AI and solvent obscures the intermolecular bands of the AI dimer when the concentration of the AI dimer is much lower than the AI monomer. For comparison, we have employed NMR to study the concentration-dependent chemical shift of the proton attached to the N at the 7-position of AI and to estimate the dimerization constant: 356, 13.3, 14.7, 0.727, and 0.910 M in CCl , CHCl , CH Cl , acetone, and CH CN, respectively. The femtosecond Raman-induced Kerr effect spectroscopy and NMR results are in good agreement. © 2013 American Chemical Society. 4 3 2 2 3 3 2 2 4 3 3 2 2 3 3 4 3 2 2 3 -1 -1 -1

Intermolecular/interionic vibrational spectra of mixtures composed of 1-methyl-3-n-octylimidazolium tetrafluoroborate ionic liquid and benzene at mole fractions of 0 (i.e., neat ionic liquid), 0.2, 0.4, 0.6, 0.8, and 1.0 (i.e., neat benzene) have been investigated using femtosecond Raman-induced Kerr effect spectroscopy. The line shape of the low-frequency Kerr spectra obtained from Fourier transform analyses of the Kerr transients is strongly dependent on the composition of the mixture. By comparing the experimental spectra to calculated spectra based on experimental spectra of the neat liquids, it is evident that the spectrum is not achieved by simply combining those of the neat liquids and taking the mole fraction into consideration. Close examination of the spectral comparison results in a microscopic picture involving specific stacking of imidazolium and benzene rings that is not sufficiently stable to affect the ring librations. The quantum chemistry calculation results also support this proposal. No clear correlation between the first moment of the spectrum and the bulk parameter (i.e., the square root of the surface tension divided by the liquid density), which occurs for neat liquids, is evident. © 2013 American Chemical Society.

Specific cation-anion interactions for two pairs of isoelectronic ionic liquids (ILs) have been investigated using nuclear Overhauser effect (NOE) 2D NMR methods to explore proximities between ions. The four ILs comprise the bis(trifluoromethylsulfonyl)amide anion paired with the following cations: triethyloctylammonium, (2-ethoxyethoxy)ethyltriethylammonium, triethyloctylphosphonium, and (2-ethoxyethoxy)ethyltriethylphosphonium. Substantial interactions are observed between the anion F nuclei and all of the protons on the triethyl chains for each of the four cationic head groups. Significantly different interactions are observed for each of the four cationic tail groups and the anions. © 2013 American Chemical Society. 19

The dynamical properties of a dicationic ionic liquid (IL), 1,6-bis(3-methylimidazolium-1-yl)hexane bis(trifluoromethylsulfonyl)amide ([C (MIm) ][NTf ] ), compared to 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide ([C MIm][NTf ]), 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 (MIm) ] and [C MIm] and related to the difference of relaxation behavior between [C (MIm) ] and [C MIm] . Also, it is indicated that the librational dynamics of [NTf ] indicate a common resonance-type sharp peak that corresponds to an intermolecular motion coupled to the vibrational mode intrinsic to [NTf ] . 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 appears for [C (MIm) ][NTf ] , while we do not see it for [C MIm][NTf ]. 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 (MIm) ][NTf ] that dynamical heterogeneous behavior strongly correlates with structural variations or heterogeneity. © 2012 American Chemical Society. 6 2 2 2 3 2 6 2 3 6 2 3 2 2 6 2 2 2 3 2 6 2 2 2 2+ + 2+ + - - -1

X-ray scattering experiments and molecular dynamics simulations have been performed to investigate the structure of four room temperature ionic liquids (ILs) comprising the bis(trifluoromethylsulfonyl)amide (NTf2 ) anion paired with the triethyloctylammonium (N2228 ) and triethyloctylphosphonium (P2228 ) cations and their isoelectronic diether analogs, the (2-ethoxyethoxy)ethyltriethylammonium (N222(2O2O2) ) and (2-ethoxyethoxy)ethyltriethylphosphonium (P222(2O2O2) ) cations. Agreement between simulations and experiments is good and permits a clear interpretation of the important topological differences between these systems. The first sharp diffraction peak (or prepeak) in the structure function S(q) that is present in the case of the liquids containing the alkyl-substituted cations is absent in the case of the diether substituted analogs. Using different theoretical partitioning schemes for the X-ray structure function, we show that the prepeak present in the alkyl-substituted ILs arises from polarity alternations between charged groups and nonpolar alkyl tails. In the case of the diether substituted ILs, we find considerable curling of tails. Anions can be found with high probability in two different environments: close to the cationic nitrogen (phosphorus) and also close to the two ether groups. For the two diether systems, anions are found in locations from which they are excluded in the alkyl-substituted systems. This removes the longer range (polar/nonpolar) pattern of alternation that gives rise to the prepeak in alkyl-substituted systems. © 2012 American Chemical Society. - + + + +

We report here the low-frequency spectra, resulting from the intermolecular/interionic vibrational dynamics, of aqueous mixtures of an ionic liquid, 1-methyl-3-n-octylimidazolium tetrafluoroborate, with the H O mole fractions of 0.2, 0.4, and 0.6 and the neat ionic liquid and H O within the frequency range of 0.1-700 cm by means of femtosecond Raman-induced Kerr effect spectroscopy. Addition of H O induces tiny effects on the line shape of the low-frequency Kerr spectrum of the ionic liquid: ca. a 2 cm red shift in the first moment of the low-frequency spectrum has been observed for a transition from the neat ionic liquid to the binary mixture containing 0.6 mol fraction of H O. Surface tension and liquid density of the mixture also accompany minimal changes upon addition of H O. These results suggest that H O molecules localize at the interface between the ionic and nonpolar regions, and the interionic interaction in the ionic region is weakly perturbed by the existence of H O. On the other hand, successive addition of H O in the mixture slows down the picosecond overdamped relaxation process measured in the 3-300 ps range even though the shear viscosity of the mixture decreases substantially. © 2012 American Chemical Society. 2 2 2 2 2 2 2 2 -1 -1

The 1-methyl-3-trimethylsilylmethylimidazolium tetrafluoroborate ([Si-MIm][BF ]) liquid has been crystallized under high pressure of 400 MPa. The liquid-crystal phase transition has been detected and the crystal structure of such prepared ionic crystal has been determined by X-ray diffraction. © 2012 Elsevier B.V. All rights reserved. 4

In this minireview, the features of low-frequency spectra within the frequency range 0-200 cm for aromatic and nonaromatic cation based ionic liquids obtained by femtosecond Raman-induced Kerr effect spectroscopy are reviewed. For aromatic cation based ionic liquids, the aromatic group of the cations is largely responsible for the spectral line shape due to their larger polarizability anisotropy volume and more polarizable nature than nonaromatic cations. The low-frequency Kerr spectra are also compared with the bulk properties of the ionic liquids. The differences in the relationship of the first moment of the low-frequency spectrum band and the bulk properties between the aromatic and nonaromatic cation based ionic liquids with respect to the natures of constituent ions and microscopic aspects are discussed. For aromatic cation based ionic liquids, the ionic region is more pronounced than the nonpolar region in their low-frequency Kerr spectra. In contrast, the ionic and nonpolar regions of nonaromatic cation based ionic liquids are likely to be captured due to the weaker signal of the cationic region. Also, the low-frequency Kerr spectra of the nonaromatic analogues are influenced by their weaker segregation as compared to aromatic cation based ionic liquids. © 2012 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim. -1

X-ray scattering data from four pairs of ionic liquids (ILs) are compared. The alkyl-substituted cations show a first sharp diffraction peak between 3 and 4 nm that is not observed for ILs having cations with ether- or hydroxy-substitutions. These observations indicate a significant difference in the intermediate range order for these liquids. © 2012 Royal Society of Chemistry. −1

Frequency-dependent shear viscosities of ammonium- and phosphonium-based ionic liquids with an oxyethylene chain were determined between 5 and 205 MHz, and compared with those of corresponding ionic liquids with an alkyl chain. The shear relaxation spectra show that the substitution of the alkyl chain with the oxyethylene one lowers shear viscosity through the reduction of relaxation time, which is attributed to the higher flexibility of the latter. Comparing the relaxation spectra of ionic liquids with those of non-ionic ones, higher shear viscosities of ionic liquids are ascribed to the larger high-frequency shear modulus due to the interionic Coulombic interaction. © 2011 Elsevier B.V. All rights reserved.

The ultrafast dynamics, including the intermolecular vibrations and the diffusive orientational dynamics, of the neat C symmetry condensed ring aromatic molecular liquids benzofuran, 1-fluoronaphtalene, and quinoline were investigated for the first time by means of femtosecond Raman-induced Kerr effect spectroscopy. To understand the features of these C condensed ring aromatic molecular liquids, reference singular aromatic molecular liquids, furan, fluorobenzene, pyridine, and benzene, were also studied. High quality low-frequency Kerr spectra of the aromatic molecular liquids were obtained by Fourier-transform deconvolution analysis of the measured Kerr transients. The Kerr spectra of the C condensed ring aromatic molecular liquids are bimodal, as are those of the reference singular aromatic molecular liquids. The first moment of the intermolecular vibrational spectrum and the peak frequencies of the high- and low-frequency components in the broad spectrum band were compared with their molecular properties such as the rotational constants, molecular weight, and intermolecular (bimolecular) force. The comparisons show that the molecular volume (related to molecular weight and rotational constants) is a dominant property for the characteristic frequency of the entire intermolecular vibrational spectrum. The observed intramolecular vibrational modes in the Kerr spectra of the aromatic molecular liquids were also assigned on the basis of the ab initio quantum chemical calculation results. In their picosecond diffusive orientational dynamics, the slowest relaxation time constant for both the condensed ring and singular aromatic molecular liquids can be accounted for by the simple Stokes - Einstein - Debye hydrodynamic model. (Figure presented) © 2011 American Chemical Society. s s s

The conductivity relaxation dynamics of the room-temperature ionic liquid 1-methyl-3-trimethylsilylmethylimidazolium tetrafluoroborate ([Si-MIm][BF ]) have been studied by broadband conductivity relaxation measurements at ambient pressure and elevated pressures up to 600 MPa. For the first time, several novel features of the dynamics have been found in a room-temperature ionic liquid. In the electric loss modulus M″(f) spectra, a resolved secondary β-conductivity relaxation appears, and its relaxation time τ shifts on applying pressure in concert with the relaxation time τ of the primary α-conductivity relaxation. The spectral dispersion of the α-conductivity relaxation, as well as the fractional exponent (1 - n) of the Kohlrausch-Williams-Watts function that fits the spectral dispersion, is invariant to various combinations of pressure and temperature that keep τ constant. Moreover, τ is unchanged. Thus the three quantities, τ , τ , and n, are coinvariant to changes in pressure and temperature. This strong connection to the α-conductivity relaxation shown by the β-conductivity relaxation in [Si-MIm][BF ] indicates that it is the analogue of the Johari-Goldstein β-relaxation in nonionically conducting glass-formers. The findings have fundamental implications on theoretical interpretation of the conductivity relaxation processes and glass transition in ionic liquids. It is also the first time such a secondary conductivity relaxation or the primitive conductivity relaxation of the coupling model has been fully resolved and identified in M″(f) in any ionically conducting material that we know of. © 2011 American Chemical Society. 4 β α α β α β 4

The low frequency Raman spectral density associated with the intermolecular hydrogen-bonding interaction of benzoic acid in chloroform was investigated through the ultrafast optically-heterodyne-detected optical Kerr effect. The low-frequency solute Raman spectrum was obtained by Fourier transform analysis and subtraction of the solvent spectrum from the solution spectrum. The resulting difference spectrum has a broad band below 150 cm with a peak at around 80 cm . Previous studies of aromatic liquids suggest that the origin of such a low-frequency band is librational motion, although intermolecular hydrogen-bonding modes in benzoic acid may also contribute. To clarify these contributions to the low-frequency band, methyl benzoate was used to estimate the librational component; its structure is similar to benzoic acid, but it forms no intermolecular hydrogen bonds. Both librational and intermolecular modes were found to contribute to the low-frequency Raman spectrum of the dimer and thus can be separated. These experimental results were compared with the results of density functional theory calculations. In addition, the effect of deuteration on the Raman spectrum was also investigated. © 2011 American Institute of Physics. -1 -1

The interionic vibrations in imidazolium-based dicationic ionic liquids (ILs) containing the bis(trifluoromethylsulfonyl)amide ([NTf ] ) counteranion were investigated using femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy. The microscopic nature of the dicationic ILs ([C (MIm) ][NTf ] , where n = 6, 10, and 12; MIm = N-methylimidazolium) was compared with that of the corresponding monocationic ILs ([C MIm][NTf ], where n = 3, 5, and 6) used as reference samples. Low-frequency Kerr spectra within the frequency range 0-200 cm of the ILs revealed that (i) the spectral profile of the dicationic ILs as well as that of the corresponding monocationic ILs is bimodal; (ii) the difference in the spectral shapes of the dicationic and monocationic ILs is greater for [C (MIm) ][NTf ] and [C MIm][NTf ] than for the ILs with longer alkylene linker/alkyl groups, namely [C (MIm) ][NTf ] and [C MIm][NTf ], and [C (MIm) ][NTf ] and [C MIm][NTf ]; (iii) the small difference between the dicationic and monocationic ILs is confirmed by the relative intensity of the low-frequency component (ca. 17 cm ) to the high-frequency component (ca. 70 cm ); and (iv) the spectral profiles of the three dicationic ILs are not very different, but the line-shape of the low-frequency Kerr spectrum of 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide ([C MIm][NTf ]) is significantly different from those of the other two monocationic ILs whose cations have a longer alkyl group. The distinguished line-shape of the low-frequency Kerr spectrum of [C MIm][NTf ] from the other ILs can be accounted for by the homogeneous nature in the microstructure of the IL, but the other ILs indicate microsegregation structures due to the longer nonpolar alkylene linker or alkyl group in the cations. © 2011 American Chemical Society. 2 n 2 2 2 n 2 6 2 2 2 3 2 10 2 2 2 5 2 12 2 2 2 6 2 3 2 3 2 - -1 -1 -1

We report the quality anisotropic intermolecular vibrational spectra within the frequency range 0.5-800 cm of four C CXY molecular liquids, CHCl , CHBr , CFBr , and CBrCl , by means of femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy. The results show that the first moment of the intermolecular vibrational spectrum is proportional to the square root of the value of the surface tension divided by the liquid density. This implies that the intermolecular vibrational spectrum reflects the bulk properties of the liquids. To understand the molecular-level aspects of the intermolecular vibrational spectra of the liquids, the spectra are compared with the molecular properties such as molecular weight, rotational constants, and bimolecular interaction energy. Overall, the first moment of the spectrum moderately correlates to the inverse square roots of both the molecular weight and the fast rotational constant. Therefore, the molecular properties are responsible for the intermolecular vibrational spectrum. Plots of the first moment of the intermolecular vibrational spectrum vs the square root of the value of the simple bimolecular interaction energy divided by the molecular surface area and the molecular weight show a linear correlation in the case of the oblate symmetric top molecular liquids, CHCl , CHBr , and CFBr . However, CBrCl , which is a prolate symmetric top molecular liquid, does not show the same correlation for the oblate molecular liquids. © 2011 American Chemical Society. -1 3v 3 3 3 3 3 3 3 3 3

We report the data of liquid density, thermal properties including glass transition temperature, melting point, and decomposition temperature, surface tension, and shear viscosity for imidazolium-based dicationic ionic liquids with the anions of bis(trifluoromethylsulfonyl)amide, bis(pentafluoroethylsulfonyl) amide, tetrafluoroborate, and nitrate. To find the unique and general features of the dicationic ionic liquids, data of their corresponding monocationic ionic liquids are also summarized. The results of the dicationic ionic liquids showed that the density was high; the glass transition temperature and melting point were high, and they were thermally stable. Also the surface tension was large, and the shear viscosity was high in comparison with the reference monocationic ionic liquids. The data of the physical properties including liquid density, surface tension, and shear viscosity of the ionic liquids were also compared with that of alkanediols and alkyl alcohols to find the alkyene-linker and alkyl-group dependences in the ionic liquids and alcohols. © 2011 American Chemical Society.

We investigated the ultrafast dynamics in 1-butyl-3-methylimidazolium-based ionic liquids with two series of anions, (1) cyano-group substituted anions (thiocyanate [SCN] , dicyanamide [N(CN) ] , and tricyanomethide [C(CN) ] ) and (2) trifluoromethylsulfonyl-group substituted anions (trifluoromethanesulfonate [OTf] , bis(trifluoromethylsulfonyl)amide [NTf ] , and tris(trifluoromethylsulfonyl)methide [CTf ] ). This was done by femtosecond Raman-induced Kerr effect spectroscopy. From the Fourier transform Kerr spectra of the ionic liquids, the low-frequency spectrum of 1-butyl-3-methylimidazolium tricyanomethide shows a low-frequency shift compared to the ILs with the other cyano-group substituted anions due to the planar structures of the cation and the anion. The relative amplitude of the low-frequency band at approximately 20 cm compared to the entire broad spectrum for the ionic liquids with trifluoromethylsulfonyl-group substituted anions becomes larger with the order [OTf] < [NTf ] ≈ [CTf ] . This vibrational band can be attributed to the librational motion of anions and/or the coupling of the translational and reorientational motions. © 2011 American Chemical Society. - - - - - - -1 - - - 2 3 2 3 2 3

We observed the low-frequency Raman-active intermolecular vibrational modes of 7-azaindole in CCl by femtosecond Raman-induced Kerr effect spectroscopy. To understand the dynamical aspects and vibrational modes of 7-azaindole in the solution, the ultrafast dynamics of 1-benzofuran in CCl was also examined as a reference and ab initio quantum chemistry calculations were performed for 7-azaindole and 1-benzofuran. The cooperative hydrogen-bonding vibrational bands of 7-azaindole dimer in CCl appeared at 89 cm and 105 cm represent the overlap of stagger and wheeling modes and the intermolecular stretching mode, respectively. They are almost independent of the concentration in the solution. We further found from the low-frequency differential Kerr spectra of the solutions with neat CCl that the intermolecular motion in the low frequency region below 20 cm was less active in the case of 7-azaindoleCCl than in the case of 1-benzofuranCCl . The slow orientational relaxation time in 7-azaindoleCCl is ∼3.5 times that in 1-benzofuranCCl because of the nature of the dimerization of 7-azaindole. © 2011 American Institute of Physics. 4 4 4 4 4 4 4 4 -1 -1 -1

In this study, we have investigated the heavy atom substitution effects on the ultrafast dynamics in nonaromatic cation-based ionic liquids, as well as the static physical properties such as shear viscosity, surface tension, glass transition temperature, and melting point. Phosphonium-based ionic liquids show lower shear viscosities and lower glass transition temperatures than their corresponding ammonium-based ionic liquids. We have also examined the substitution of a (2-ethoxyethoxy)ethyl group for an octyl group in ammonium and phosphonium cations and found that the (2-ethoxyethoxy)ethyl group reduces the shear viscosity and increases the surface tension. From the results of the ultrafast dynamics, including intra- and interionic vibrations and reorientational relaxation in the ammonium- and phosphonium-based ionic liquids measured by means of femtosecond optically heterodyne-detected Raman-induced Kerr spectroscopy, we have found that the first moment of low-frequency Kerr spectrum, omitting the contributions of clear intraionic vibrational modes, correlates to the square root of surface tension divided by density. This fact indicates that heavy atom substitution in ionic liquids provides a weaker interionic interaction arising from the larger ionic volume. On the other hand, the ether group in the cations gives the stronger interionic interaction but with a more flexible and/or less segregated nature in the ILs than the alkyl group. © 2010 American Chemical Society.

We have investigated the microscopic aspects for ionic liquid-H O systems by Raman and IR spectroscopies. Ionic liquids studied here are a series of 1-alkyl-3-methylimidazolium cations (alkyl groups: ethyl, butyl, hexyl, octyl, and decyl groups) with the anions of tetrafluoroborate and bis(trifluoromethanesulfonyl)amide. Polarities of the ionic liquid-H O systems have also been measured by means of a solvatochromic dye, betaine 33. Vibrational bands of the anions shift to the higher frequency with the higher water content. We have also found that the magnitude of the frequency shifts of the anions vibrational modes by adding water becomes smaller with the longer alkyl group of cation. From the comparison of the vibrational spectroscopic result with the result of the solvatochromic experiment, it has become clear that the frequency shift of the vibrational modes of anions almost correlates with the polarity. On the other hand, the feature of the vibrational band of water stretching mode is not really changed among the cations with the different alkyl groups. This evidence implies that the water aggregations localize at ionic regions and the water state does not really depend on the alkyl group of cation. © 2010 American Chemical Society. 2 2

Following the preceding spectroscopic study, we further investigate atomic mass effects of [XF ] in 1-butyl-3-methylimidazolium cation ([BMIm] ) based ionic liquids (ILs) on dynamical natures by a computational approach in this study. We carry out the molecular dynamics simulations for 1-butyl-3-methylimidazolium cation based ILs ([BMIm][PF ], [BMIm][AsF ], and [BMIm][SbF ]) with the development of the force fields of [AsF ] and [SbF ] by an ab initio calculation. We have calculated density of state (DOS) and velocity autocorrelation function (VACF) profiles, polarizability time correlation function (TCF) and Kerr spectra, intermediate scattering functions, and dynamical structure factors. The decomposition analysis has been also carried out to understand the ion species and types of motion. From these computational studies, we find that the contribution of the reorientation of cations and anions mainly governs the Kerr spectrum profile in all three ILs, while the contribution of the collision-induced and cross terms, which are related to translational motions including coupling with librational motion, is not large at higher frequencies than 50 cm . It is suggested that, with the atom substitution effects of anion units on interionic interactions, many properties in ILs are controllable. In addition, it is emphasized in this study that atomic mass effects in ILs are accessible through a complementary approach of both experimental and theoretical approaches. © 2009 American Chemical Society. 6 6 6 6 6 6 - + - - -