1998 Fiscal Year Final Research Report Summary
Characteristic Molecular Structures of Electronically Excited Species Studied by Ultrafast Time-Resolved Infrared Spectroscopy in the Fingerprint Region.
| Project/Area Number |
09640597
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | The University of Tokyo |
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Principal Investigator |
OKAMOTO Hiromi The University of Tokyo, School of Science, Associate Professor, 大学院・理学系研究科, 助教授 (20185482)
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| Project Period (FY) |
1997 – 1998
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| Keywords | infrared spectroscopy / fingerprint region / electronically excited states / time-resolved spectroscopy / dichroism / ultrafast phenomena / optically heterodyned detection / molecular structure |
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| Research Abstract |
In this research we have tried to improve sensitivity of our apparatus for picosecond infrared spectroscopy in the fingerprint region and to measure several photochemically important electronically excited species to obtain their structural information. As for the sensitivity improvement, we have succeeded in proposing a novel method based on optically heterodyned detection of absorption anisotropy, in addition to many minor changes of apparatus. By this method amplitude of the absorption signal increases in nearly (or sometimes more than) one order of magnitude. We have then performed picosecond infrared measurements in the fingerprint region for several photochemically improtant excited species. Transient infrared spectra of S state of S^1 state of trans-stilbene are measured in acetonitrile and n-heptane solutions, and from the comparison between them and the Raman spectra of the same species, the excited molecular structures are discussed. It has been suggested that the S^1 species retains the center of symmetry in n-heptane, while the S^1 state in acetonitrile is slightly distorted from the centrosymmeric structure. A possible interpretation for this result is that the excited species is weakly polarized around the olefinic C=C bond in acetonitrle solution. As a related compound, we have also succeeded in obtaining an infrared spectrum of the excited diphenylacetylene. We have investigated transient infrared spectrum of S^1 state of 4-(dimethylamino)benzonitrile in an acetonitrile solution, which attracts much attention in relation to the TICT (twisted intramolccular charge transfer) structure. A strong band has been found in the single-bond stretching wavenumber region, which may be assigned to the C-N stretch of the bond between the C atom of the benzene ring and the N atom of the dimethylamino group. This result suggests that the C-N bond has a single-bond character in the S^1 state.
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