| Co-Investigator(Kenkyū-buntansha) |
MARIANO P.S. メリーランド大学, 化学科, 教授
MCBRIDE J.Michael Yale University, Department of Chemistry, スターリング化学実験室, 教授
HILINSKI Edwin.F. The Florida State University, Deparment of Chemistry, Associate Professor, 化学科, 助教授
DINNOCENZO J ローチェスター大学, 化学科, 助教授
GOODMAN Joshua.L. University of Rochester, Deparment of Chemistry, Associate Professor, 化学科, 助教授
WAGNER Peter J. Michigan State University, Deparment of Chemistry, Professor, 化学科, 教授
BERSON J.A. エール大学, 化学科, 教授
AKIYAMA Kimio Tohoku University, Institute for Chemical Reaction Science, Associate Proffesor, 反応研, 助教授 (10167851)
SUZUKI Takanori Hokkaido University, Graduate School of Science, Associate Professor, 理学部, 助教授 (70202132)
TAKAHASHI Yasutake Tohoku University, Graduate School of Science, Associate, 大学院・理学研究科, 助手 (70197185)
IKEDA Hiroshi Tohoku University, Graduate School of Science, Associate, 大学院・理学研究科, 助手 (30211717)
MARIANO Patrick S. University of Maryland, Department of Chemistry and Biochemistry, Professor
DINNOCENZO Joseph P. University of Rochester, Deparment of Chemistry, Associate Professor
BERSON Jerome A. Yale University, Deparment of Chemistry, Professor
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| Research Abstract |
We have studied the relationship between biradical (BR) and cation radical(CR)intermediates in the photoinduced electron-tranfer(PET)skeletal rearrangement of organic compounds. In general, a nondistonic CR of a donor substrate generated by PET from the excited state of sensitizer (A)can undergo the bond formation or bond cleavage to give a more stable distonic CR intermediates (I^<・+>). Although free distonic CRs have been often observed spectroscopically and/or captured by a trapping reagent such as molecular oxygen or alcohol, reactions of a distonic CR in an ion pair [I^<・+>/A^<・->] have not been well understood yet. There are two possibilities for the decay of a distonic CR intermediate. One is back electron transfer (BET) from A^<・-> to give a singlet or triplet BR intermediate, which give final product (s) by the bond cleavage or formation. The other one is an alternative possible sequence, i.e., bond cleavage or formation in a CR stage followed by BET.In order to know which pro
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cess is operative, we use two complementary laser techniques, time-resolved absorption spectroscopy for the direct observation of CR and BR intermediates and time-resolved photoacoustic calorimetry for the determination of energy of [I^<・+>/A^<・->]. As result, we found three PET reactions that proceed through both CR and BR intermediates. The first is the PET degenerate Cope rearrangement of 2,5-diaryl-1,5-hexadiene, which proceeds in a CR cyclization-BR cleavage mechanism through 1,4-diarylcyclohexa-1,4-diyl CR and 1,4-diarylcyclohexa-1,4-diyl BR.The second example is the degenerate methylenecyclopropane rearrangement of 2,2-diarylmethylenecyclopropane induced by PET,which involves a trimethlenemethane CR (TMM^<・+>) and corresponding BR (TMM). The last case is the generation of singlet and triplet tetramethyleneethane BRs by cyclization of 5,5-dimethy1-2,3-bis (1-phenylvinyl) cyclopentadiene CR.
Those three PET reactions provided an intriguing conclusion that BET in an ion pair is an important key process which connects CR chemistry with BR chemistry. This conclusion is quite noteworthy since, up to the present, BET was usually considered as an energy wasting process. Less
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