2001 Fiscal Year Final Research Report Summary
MOLECULAR ASPECTS OF DYNAMICS IN REACTION PROCESSES AND MOLECULAR INTERACTIONS IN SOLUTION
| Project/Area Number |
10102007
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| Research Category |
Grant-in-Aid for Specially Promoted Research
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| Allocation Type | Single-year Grants |
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| Review Section |
Chemistry
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| Research Institution | Osaka University |
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Principal Investigator |
OKADA Tadashi Graduate School of Engineering Science, Osaka University, Professor, 大学院・基礎工学研究科, 教授 (40029442)
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| Co-Investigator(Kenkyū-buntansha) |
NAGASAWA Yutaka Graduate School of Engineering Science, Osaka University, Research Associate, 大学院・基礎工学研究科, 助手 (50294161)
NAKASHIMA Satoru Graduate School of Engineering Science, Osaka University, Research Associate, 大学院・基礎工学研究科, 助手 (80263234)
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| Project Period (FY) |
1998 – 2001
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| Keywords | SOLVATION DYNAMICS / RADIATIONLESS PROCESSES / PHOTON ECHO / FEMTOSECOND LASER SPECTROSCOPY / MULTIDIMENSIONAL ANALYSIS / CORRELATION BETWEEN MOLECULAR DYNAMICS |
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| Research Abstract |
The focus of our research project is the ultrafast spectroscopic study of photophysical and photochemical processes in solution and glasses. To elucidate the dynamics of the solute-solvent interactions in chemical and biological processes by the femtosecond laser spectroscopy, physico-chemical processes including solvation, energy relaxation, electron/proton transfer, and geminate recombination between photodissociation products are under investigation.
Cavity-dumped Kerr-lens mode-locked Ti : sapphire laser(12 fs) and Cr : forsterite laser(26 fs) were developed for the measurements of pump-probe, three-pulse photon echo, Kerr-gate emission, optical Kerr, and fluorescence up-conversion spectroscopy.
We have carried out ultrafast pump-probe measurements of TPM dyes with a time resolution of 30 fs. The signal decays in a multiexponential manner, and the slower components showed stronger linear dependence on the solvent viscosity than the faster ones. The activation energies and effective v
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olumes were larger for slower decays. The results can be explained by the effect of the time dependent viscosity or the hierarchy structure of the solvation shell.
Using a blue copper protein, we have studied protein dynamics associated with optical excitation and radiationless deactivation of the charge transfer state by an ultrafast pump-probe spectroscopy. A coherent low frequency vibrational mode of which the phase shifted from those of the other localized Raman modes was observed. This low frequency mode most probably can be attributed to the delocalized mode including the protein skeletal motion.
We employ a reference interaction-site model theory to estimate the relaxation dynamics of the average energy of solute-solvent systems as well as the time-dependent radial distribution functions of solvents viewed from the solute molecule. The theoretical results indicate that the rearrangement of the second solvent shell is about an order of magnitude slower compared with that of the first shell. We suggest that the slower relaxation of further solvent shells can play a significant role in the dynamic relaxation of the inhomogeneous spectral width, which has been observed in our previous experiment of the time resolved hole-burning and fluorescence spectroscopy.
Molecular dynamics simulation of a simple model system of the geminate radical pair in solution has been performed to elucidate the dynamic behavior of the dipole radicals in nonpolar and polar solvents. The dipole-dipole interaction stabilized the radical pair with a small separation. The dipole pair can be the precursor of the experimentally observed sandwich radical dimer. The conformation of the dipole pair may not be favorable for the recombination of the radicals, which can be the reason of the high escape probability observed for the p-aminophenylthiyl radical.
We have demonstrated two-dimensional three-pulse photon echo measurement of a dye doped PMMA at 30K. Rephasing and echo formation were still clear even when the population period, T, was extended to > 100 ps. The results indicate that the echo signal itself has the vibrational structure. Less
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