Low-Frequency Spectra of Hydrated Ionic Liquids with Kosmotropic and Chaotropic Anions.

In this study, we investigated the water concentration dependence of the intermolecular vibrations of two hydrated ionic liquids (ILs), cholinium dihydrogen phosphate ([ch][dhp]) and cholinium bromide ([ch]Br), using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES). The anions of the former and latter hydrated ILs are kosmotropic and chaotropic, respectively. We found that the spectral peak of ∼50 cm shifted to the low-frequency side in hydrated [ch][dhp], indicating the weakening of its intermolecular interactions.

Physical Properties and Low-Frequency Polarizability Anisotropy and Dipole Responses of Phosphonium Bis(fluorosulfonyl)amide Ionic Liquids with Pentyl, Ethoxyethyl, or 2-(Ethylthio)ethyl Group.

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 of three synthesized ionic liquids (ILs), triethylpentylphosphonium bis(fluorosulfonyl)amide ([P][NF]), ethoxyethyltriethylphosphonium bis(fluorosulfonyl)amide ([P][NF]), and triethyl[2-(ethylthio)ethyl]phosphonium bis(fluorosulfonyl)amide ([P][NF]), at various temperatures using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and terahertz time-domain spectroscopy (THz-TDS).

Theoretical Investigation of Dissolution and Decomposition Mechanisms of a Cellulose Fiber in Ionic Liquids.

We carry out detailed computational investigations of the decomposition and dissolution processes of a cellulose I fiber in the ionic liquid (IL) solvent, [CMIm][OAc]. First, we investigated the properties of the interactions between cellulose chains in the cellulose fiber, including interchain H-bonds and stacking interactions, with the quantum and molecular mechanics (QM/MM) methods, employing a microscopic solvent model. From the calculation results, it is indicated that interchain interaction energies are largely influenced in the axial direction by the solvent effects of the IL and that the degree of interactions depends on the site of the glucose unit, compared to that in the equatorial (parallel) direction.

Femtosecond Raman-Induced Kerr Effect Study of Temperature-Dependent Intermolecular Dynamics in Imidazolium-Based Ionic Liquids: Effects of Anion Species and Cation Alkyl Groups.

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 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.

Dicationic versus monocationic ionic liquids: distinctive ionic dynamics and dynamical heterogeneity.

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](+).

Microscopic aspects in dicationic ionic liquids through the low-frequency spectra by femtosecond Raman-induced Kerr effect spectroscopy.

The interionic vibrations in imidazolium-based dicationic ionic liquids (ILs) containing the bis(trifluoromethylsulfonyl)amide ([NTf(2)](-)) counteranion were investigated using femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy. The microscopic nature of the dicationic ILs ([C(n)(MIm)(2)][NTf(2)](2), where n = 6, 10, and 12; MIm = N-methylimidazolium) was compared with that of the corresponding monocationic ILs ([C(n)MIm][NTf(2)], where n = 3, 5, and 6) used as reference samples. Low-frequency Kerr spectra within the frequency range 0-200 cm(-1) 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(6)(MIm)(2)][NTf(2)](2) and [C(3)MIm][NTf(2)] than for the ILs with longer alkylene linker/alkyl groups, namely [C(10)(MIm)(2)][NTf(2)](2) and [C(5)MIm][NTf(2)], and [C(12)(MIm)(2)][NTf(2)](2) and [C(6)MIm][NTf(2)]; (iii) the small difference between the dicationic and monocationic ILs is confirmed by the relative intensity of the low-frequency component (ca.

Ultrafast dynamics in 1-butyl-3-methylimidazolium-based ionic liquids: a femtosecond Raman-induced Kerr effect spectroscopic study.

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)(2)](-), and tricyanomethide [C(CN)(3)](-)) and (2) trifluoromethylsulfonyl-group substituted anions (trifluoromethanesulfonate [OTf](-), bis(trifluoromethylsulfonyl)amide [NTf(2)](-), and tris(trifluoromethylsulfonyl)methide [CTf(3)](-)). 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.

Atom substitution effects of [XF6]- in ionic liquids. 1. Experimental study.

We have investigated the interionic vibrational dynamics of 1-butyl-3-methylimidazolium cation ([BMIm]+) based ionic liquids with the anions of [PF6]-, [AsF6]-, and [SbF6]- as well as the static physical properties, such as shear viscosity and liquid density. Shear viscosity for the ionic liquids becomes lower with the heavier atom anion: [BMIm][PF6]>[BMIm][AsF6]>[BMIm][SbF6]. This tendency for heavy atom substitution for the anion results from weaker interionic interaction caused by larger anion volume.

Atom substitution effects of [XF6]- in ionic liquids. 2. Theoretical study.

Following the preceding spectroscopic study, we further investigate atomic mass effects of [XF6]- 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][PF6], [BMIm][AsF6], and [BMIm][SbF6]) with the development of the force fields of [AsF6]- and [SbF6]- 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.

Solvent motions and solvation processes in a short-time regime: effects on excited-state intramolecular processes in solution.

We propose a method for treating equation of motions for atoms taking into account the inertial term with an interaction site model for capturing solvent dynamics attributed to solvent motions in a short-time regime, t < 100 fs. We show a prescription for solving the equation which governs the development of the fluctuation of solvent number density with the inertial term, and the results of the van Hove space-time correlation function of water are compared with those by a molecular dynamics simulation. Also, the procedure is applied to the study of solvation dynamics of the simplest betaine dye molecule pyridinium N-phenoxide in water in the excited state.

Consequences of strong coupling between solvation and electronic structure in the excited state of a betaine dye.

The electronic ground and excited-state structures of the betaine dye molecule pyridinium- N-phenoxide [4-(1-pyridinio)phenolate] are investigated both in the gas phase and in aqueous solution, using the reference interaction site model self-consistent-field (RISM-SCF) procedure within a CASSCF framework. We obtain the total free energy profiles in both the ground and excited states with respect to variation in the torsion angle between the phenoxide and pyridinium rings. We analyze the effect of solvent on the variation of the solute dipole moment and on the charge transfer character in the excited state.

Optimal charge and charge response determination through conformational space: global fitting scheme for representative charge and charge response kernel.

We propose a global fitting scheme derived in the least-squares sense to estimate the optimal partial charge and charge response kernel (CRK), partial differential(Q(a))/partial differential(V(b)), with the data collected from conformational space sampling. We applied the global fitting method to the 1-butanol system and show the performance and accuracy of our global fitting procedure. In addition, we chose 1-pentanol as the test system for electronic structure change through conformational change and applied the global fitting method to it.

Theoretical study of temperature and solvent dependence of the free-energy surface of the intramolecular electron-transfer based on the RISM-SCF theory: application to the 1,3-dinitrobenzene radical anion in acetonitrile and methanol.

The free-energy surfaces along the intramolecular electron-transfer reaction path of the 1,3-dinitrobenzene radical anion in acetonitrile and methanol are investigated with the reference interaction site model self-consistent field theory. Although acetonitrile and methanol have similar values of the dielectric constant, the free-energy profiles are quite different. In the methanol solution, the charge is strongly localized on one of the nitrile substituents due to a strong hydrogen bond between 1,3-dinitrobenzene and the solvent, while the polarization is not so large in the case of acetonitrile.

Extended treatment of charge response kernel comprising the density functional theory and charge regulation procedures.

We propose an extended treatment of the charge response kernel (CRK), (partial differential Q(a)/partial differential V(b)), which describes the response of partial charges on atomic sites to external electrostatic potential, on the basis of the density functional theory (DFT) via the coupled perturbed Kohn-Sham equations. The present CRK theory incorporates regulation procedures in the definition of partial charges to avoid unphysical large fluctuation of the CRK on "buried" sites. The CRKs of some alcohol and organic molecules, methanol, ethanol, propanol, butanol, dimethylsulfoxide (DMSO), and tetrahydrofuran (THF) were calculated, demonstrating that the new CRK model at the DFT level has greatly improved the performance of accuracy in comparison with that at the Hartree-Fock level previously proposed.

Polarizable solute in polarizable and flexible solvents: simulation study of electron transfer reaction systems.

A polarizable solute model, based on the empirical valence bond approach, is developed and applied to electron transfer (ET) reactions in polarizable and flexible water solvents. The polarization effect is investigated in comparison with a nonpolarizable solute and solvent model. With free energy curves constructed by a molecular dynamics simulation, the activation energy barrier and the reorganization energy related to ET processes are investigated.