1997 Fiscal Year Final Research Report Summary
CONTROL OF PHOTOCHEMICAL REACTIONS BY HYDROGEN BONDING
| Project/Area Number |
08640666
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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 |
Organic chemistry
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| Research Institution | UNIVERSITY OF TSUKUBA |
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Principal Investigator |
ARAI Tatsuo UNIVERSITY OF TSUKUBA,DEPARTMENT OF CHEMISTRY PROFESSOR, 化学系, 教授 (50151139)
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| Project Period (FY) |
1996 – 1997
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| Keywords | PHOTOISOMERIZATION / HYDRGEN TRANSFER / TAUTOMERIZATION / EXCITED STATE / FLUORESCENCE |
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| Research Abstract |
We have investigated the effect of hydrogen bonding to control the efficiency and the mode of photochemical isomerization. Furthermore, novel photoinduced hydrogen atom transfer to give the tautomer have been studied.
We found a co-operative effect of intramolecular hydrogen bonding and solvent to control the efficiency and the selectivity of photoisomerization in an olefin with a pyrrole ring and a quinoxaline ring (I). In benzene, I underwent one-way trans*cis photoisomerization due to the intramolecular hydrogen bonding. Thus, cis-I did not undergo cis-to-trans isomerization, but undergo intramolecular hydrogen atom transfer to give the tautomer as revealed by the observation of the fluorescence emission with considerably large Stokes-shift. One the other hand, the cis-to-trans isomerization prevails over trans-to-cis isomerization in methanol by making an intermolecular hydrogen bonding.
In 2'-hydroxychalcone (II), we found a novel one-way cis*trans isomerization induced by the intramolecular hydrogen atom transfer in the triplet state based on the results by laser transient spectroscopy.
We also found an novel effect of formyl group on the behavior of intramolecularly hydrogen bonded compound ; the introduction of the formyl group increased the efficiency of hydrogen atom transfer to give the tautomer. Thus, 2 [2- (2-pyridy) ethenyl] pyrrole-5-carboxaldehyde III with formyl group at the pyrrole ring exhibited considerably high quantum efficiency of fluorescence emission from the tautomer produced by intramolecular hydrogen atom transfer, although the intersystem crossing to the triplet state is also accelerated as revealed from the observation of the quantum chain process.
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