2004 Fiscal Year Final Research Report Summary
Laser spectroscopic research on unconventional hydrogen bonds involving borane
| Project/Area Number |
14204057
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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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 | Tohoku University |
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Principal Investigator |
FUJII Asuka Tohoku University, Graduate School of Science, Associate professor, 大学院・理学研究科, 助教授 (50218963)
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| Co-Investigator(Kenkyū-buntansha) |
MAEYAMA Toshihiko Center of higher education promotion, Research associate, 高等教育開発推進センター, 助手 (20250673)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Hydrogen bond / Molecular clusres / Intermolecular structure / Laser spectroscopy / Vibrational spectroscopy |
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| Research Abstract |
1.Geometric structures and the excited-state proton-dislocation in size-selected clusters of salicylic acids (salicylic acid and 5-methoxysalicylic acid) with water or methanol were studied by using laser spectroscopic techniques. Fluorescence excitation, dispersed fluorescence, and infrared (IR) spectra of those clusters in supersonic jets were examined for both the electronic ground and first excited states. The geometric structures of the clusters were determined on the basis of the IR spectra of the OH stretch region with a help of quantum chemical calculations. The hydroxyl group of the water or methanol moiety in the clusters forms a ring involving the carboxylic group of the salicylic acid moiety. The intramolecular hydrogen bond in the salicylic acid moiety is still held upon the cluster formation. The puzzling IR spectra in the electronic excited state were analyzed in combination with a partial deuteration study. The IR spectra in the excited state and dispersed fluorescence
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spectra indicated that the intramolecular excited state proton dislocation is hardly affected by the microsolvation with water or methanol, in contrast with the strong suppression of the dislocation in the self-salvation. A drastic reduction of the acidity of the carboxylic OH upon the electronic excitation was also found.
2.Substitution effects on the excited state intramolecular proton transfer (ESIPT) in the salicylic acid (SA) frame were studied by electronic and infrared spectroscopy of jet-cooled 5-methoxylsalicylic acid (5-McOSA), 5-methylsalicylic acid (5-MeSA), 5-fluorosalicylic acid (5-FSA), 6-fluorosalicylie acid (6-FSA), and methyl salicylate (MS). Infrared spectra were measured in the 3 mm region for both the electronic ground (S_0) and first excited (S_1) states. The electronic excitation/emission spectra of 5-MeSA and 6-FSA showed the typical spectral features of ESIPT, which have been found in the spectra of SA. On the other hand, 5-MeOSA and 5-FSA exhibit a mirror-image relation between their excitation and emission spectra, which has been regarded as a result of the suppression of ESIPT. Despite of such a remarkable difference among the electronic spectra, IR spectroscopy exhibits that a drastic change of the phenolic OH stretching vibration does occur upon the electronic excitation of all the substituted SAs, that is, the phenolic OH band of all the SAs disappears from the 3 mm region, indicating a large elongation of the phenolic O-H bond (over 0.1 Å) in S_1. This result represents that the intramolecular hydrogen-bond strength is remarkably enhanced upon the electronic excitation in all the substituted SAs. Substitution effects on ESIPT in dimers are also discussed. Less
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