title: Local structure formation in alkyl-imidazolium-based ionic liquids as revealed by linear and nonlinear Raman spectroscopy.
abstract: We show several pieces of Raman spectroscopic evidence that are indicative of local structure formation in imidazolium-based ionic liquids. Low-frequency Raman spectra of C n mimX, where C n mim stands for 1-alkyl(C n H 2 n+1 )-3-methylimidazolium cation and X represents the anion, exhibit broad bands assignable to collective modes of local structures. Spatial distributions of coherent anti-Stokes Raman scattering (CARS) signals from C n mim[PF 6] are consistent with local structures whose size increases with increasing n. Picosecond Raman spectra of S 1 trans-stilbene as a "picosecond Raman thermometer" show microscopic thermal inhomogeneity ascribable to local structure formation in C 2mimTf 2N and C 4mimTf 2N. We also describe two novel phenomena that we believe are relevant to extraordinary nanoenvironments generated by local structures in a magnetic ionic liquid C 4mim[FeCl 4].
authors.affiliation: Research Centre for Spectrochemistry and Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Iwata
authors.forename: Hajime
authors.initials: H
authors.lastname: Okajima
authors.forename: Satyen
authors.initials: S
authors.lastname: Saha
authors.forename: Hiro-O
authors.initials: HO
authors.lastname: Hamaguchi
mesh_terms: D048288:Imidazolines / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D010316:Particle Size; D012015:Reference Standards; D013059:Spectrum Analysis, Raman / Q000379:methods* / Q000592:standards; D013499:Surface Properties
chemical_list: D048288:Imidazolines; D052578:Ionic Liquids