"Tracing "Loose Electrons"- New Physical Chemistry with Femtosecond Time-resolved Near-infrared
Spectroscopy"
Koichi Iwata
Research Centre for Spectrochemistry, School of Science, The University of Tokyo
Abstract
We examine “elementary processes” of solution-phase chemical reactions with various time-resolved
spectroscopies. In this presentation, I report on femtosecond time-resolved fluorescence spectroscopy and
picosecond time-resolved Raman spectroscopy.
By using femtosecond time-resolved near-infrared spectrometer that covers the spectral rage of 900 to
1500 nm, we trance the dynamics of “loose electrons”, electrons loosely bound to the nuclei, with a
femtosecond time-resolution. Because the probe wavelength is longer, it is possible to measure the
time-resolved spectra of scattering powder samples with the transmission geometry, by keeping the
femtosecond time-resolution in tact. We measure the migration and decay dynamics of charge carriers
generated in photocatalytic TO2 powders. The carrier dynamics changes largely depending on the crystal
form (anatase or rutile) and the diameter. When Pt is loaded as a co-catalyst, the photogenerated electrons
are transferred to Pt in 2 ps. When the TiO2 powders are immersed in an ionic liquid, the decay process of
the generated carriers is accelerated from those in vacuum, in air, or in water. We also examine the
intramolecular charge transfer reaction in 9,9’-bianthryl. We discuss the detailed mechanism of the
photoinduced charge transfer reaction in polar and nonpolar environments based on the experimental
results from femtosecond time-resolved near-infrared spectroscopy.
When a molecule in solution is photoexcited to one of its electronically excited states with larger energy
than required for the 0-0 transition, the excess energy is deposited to the vibrational manifold. The solute
molecule then starts cooling down by dissipating the excess energy to the surrounding solvent molecules.
By monitoring the cooling process of the solute, it is possible to trance the solute-solvent energy transfer
process. We trace the cooling kinetics of the solute by measuring the picosecond time-resolved Raman
spectra of the first excited singlet (S1) state of trans-stilbene. The trans-stilbene molecule serves as a good
thermometer with a time-resolving capability of a few picoseconds. We found that there was a good
correlation between the cooling rate of S1 trans-stilbene and the thermal diffusivity of the solvent in ten
molecular solvents. Little is known, however, about the energy transfer mechanism in room-temperature
ionic liquids. We examine the cooling kinetics of S1 trans-stilbene in the ionic liquids. It is interesting to
know how the possible "local structures" in the ionic liquids, an assumption not proved in a rigorous
sense but supported by increasing number of researchers, affect the microscopic solute-solvent or
solvent-solvent energy transfer.
Biography
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Koichi IWATA
Associate Professor
Research Centre for Spectrochemistry, School of Science, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
iwata@chem.s.u-tokyo.ac.jp
81-3-5841-4600
81-3-5800-4540
Education:
The University of Tokyo, Japan
The University of Tokyo, Japan
The University of Tokyo, Japan
Title of the doctoral thesis,
and Its Applications”
B.S.
1984
M.S.
1986
Dr.Sci. 1989
“Construction of
Chemistry
Physical Chemistry
Physical Chemistry
a Microsecond Time-resolved Infrared Spectrometer
Professional Experience:
Postdoctoral Fellow, Department of Chemistry, The Ohio State University, Columbus, Ohio, USA
1989-1990
Research Associate, Molecular Spectroscopy Laboratory, Kanagawa Academy of Science and Technology,
Kawasaki, Japan
1991-1997
Associate Professor, Department of Chemistry, School of Science, The University of Tokyo, Tokyo, Japan
1997-2001
Associate Professor, Research Centre for Spectrochemistry, School of Science, The University of Tokyo,
Tokyo, Japan
2001-present