Browsing by Author "Yoshida, Kyousuke"

Now showing 1 - 4 of 4

Energy Transfer Characteristics of Lipid Bilayer Membrane in Liposome Studied with Picosecond Time-Resolved Raman Spectroscopy
(2010)
Nojima, Yuki
;
Yoshida, Kyousuke
;
Hamaguchi, Hiro-o
;
Iwata, Koichi
;
應用化學系
Local Structure and Microscopic Thermal Diffusion in Ionic Liquids Studied with Picosecond Time-resolved Raman Spectroscopy
(2010)
Yoshida, Kyousuke
;
Iwata, Koichi
;
Hamaguchi, Hiro-o
;
應用化學系
;
應用化學系分子科學碩博班
Local structures in ionic liquids probed and characterized by microscopic thermal diffusion monitored with picosecond time-resolved Raman spectroscopy
(2012-03-14)
Yoshida, Kyousuke
;
Iwata, Koichi
;
Nishiyama, Yoshio
;
Kimura, Yoshifumi
;
Hamaguchi, Hiro-o
Vibrational cooling rate of the first excited singlet (S1) state of trans-stilbene and bulk thermal diffusivity are measured for seven room temperature ionic liquids, C2mimTf2N, C4mimTf2N, C4mimPF6, C5mimTf2N, C6mimTf2N, C8mimTf2N, and bmpyTf2N. Vibrational cooling rate measured with picosecond time-resolved Raman spectroscopy reflects solute-solvent and solvent-solvent energy transfer in a microscopic solvent environment. Thermal diffusivity measured with the transient grating method indicates macroscopic heat conduction capability. Vibrational cooling rate of S1 transstilbene is known to have a good correlation with bulk thermal diffusivity in ordinary molecular liquids. In the seven ionic liquids studied, however, vibrational cooling rate shows no correlation with thermal diffusivity; the observed rates are similar (0.082 to 0.12 ps-1 in the seven ionic liquids and 0.08 to 0.14 ps-1 in molecular liquids) despite large differences in thermal diffusivity (5.4-7.5 x 10-8 m2 s-1 in ionic liquids and 8.0-10 x 10-8 m2 s-1 in molecular liquids). This finding is consistent with our working hypothesis that there are local structures characteristically formed in ionic liquids. Vibrational cooling rate is determined by energy transfer among solvent ions in a local structure, while macroscopic thermal diffusion is controlled by heat transfer over boundaries of local structures. By using " local" thermal diffusivity, we are able to simulate the vibrational cooling kinetics observed in ionic liquids with a model assuming thermal diffusion in continuous media. The lower limit of the size of local structure is estimated with vibrational cooling process observed with and without the excess energy. A quantitative discussion with a numerical simulation shows that the diameter of local structure is larger than 10 nm. If we combine this lower limit, 10 nm, with the upper limit, 100 nm, which is estimated from the transparency (no light scattering) of ionic liquids, an order of magnitude estimate of local structure is obtained as 10 nm < L < 100 nm, where L is the length or the diameter of the domain of local structure. c 2012 American Institute of Physics. [ http:// dx. doi. org/ 10.1063/ 1.3691839]
Two-step photoionization of trans-stilbene in acetonitrile via an ion-pair precursor studied with picosecond time-resolved absorption and Raman spectroscopies
(2012-02-27)
Miki, Hiroko
;
Yoshida, Kyousuke
;
Kawate, Chieko
;
Shimada, Rintaro
;
Takaya, Tomohisa
Picosecond time-resolved visible absorption and Raman spectra of trans-stilbene in acetonitrile have been measured. A new transient absorption band is observed at 440 nm, whose decay time constant coincides with that of the rise of the radical cation. In addition to the known Raman bands of the radical cation, a new Raman feature showing a fast decay is found at 1599 cm(-1). We assign the 440 nm absorption band and the 1599 cm(-1) Raman band to a precursor of the radical cation. The precursor may well be an ion pair that holds an ejected electron still around the cation. (C) 2012 Elsevier B. V. All rights reserved.