부산대학교 도서관

Theobservation of fluorescence in the visible spectral range inimidazolium-based ionic liquids, in which the peak of the fluorescencespectrum shifts with the change in the excitation wavelength by over200 nm, was reported by Samanta and co-workers (Paulet al. J. Phys. Chem. B2005, 109, 9148; Chem. Phys. Lett.2005, 402, 375), and the aggregatestructure in the bulk ionic liquid was suggested to explain this uniquephenomenon. In this work, by employing 2D-scan fluorescence spectroscopy,we identified the long- and short-wavelength fluorescence componentsof the fluorescence spectrum of 1-butyl-3-methylimidazolium tetrafluoroborate([C4MIM][BF4]), of which only the long-wavelengthfluorescence component was found to be responsible for the reportedfluorescence properties. The fluorescence intensity of the long-wavelengthcomponent decreased much faster upon dilution in aqueous mixturesthan the short-wavelength component, supporting the conclusion thatthe long-wavelength fluorescence is from molecular aggregates in thebulk ionic liquid. Fluorescence correlation spectroscopy (FCS), whichwas used to accurately account for the number density of the long-wavelengthfluorescent species in aqueous solutions of the ionic liquid, alsosuggested that the fluorescence came from aggregate structures ofmolecules in ionic liquids. [ABSTRACT FROM AUTHOR]