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].