2001 Fiscal Year Final Research Report Summary
Quantum Chemistry and Dynamics of Multi-Spin Supramolecules
| Project/Area Number |
11694061
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic chemistry
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
ASANO Motoko Tokyo Institute of Technology Department of Chemistry, Research Associate, 大学院・理工学研究科, 助手 (80201888)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIKAWA Naoto Tokyo Institute of Technology Department of Chemistry, Research Associate, 大学院・理工学研究科, 助手 (20251605)
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| Project Period (FY) |
1999 – 2000
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| Keywords | Porphyrin Dimer / unpaired electron / excited state / Time-resolved EPR / Time-resolved fluorescence / energy transfer / Time-Dependent density function theory |
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| Research Abstract |
Supramolecules undergo long-range energy and electron transfers due to their energy and/or communicative function between various units. Therefore, supramolecular system serve an excellent model of in-vivo reactions as well as a device for energy transportation. In photo-induced dynamics processes of such systems, important intermediates are often in multiple-spin states. Especially in the case that the system has an unpaired electron in the ground state, excited species have multi-centered spins, which interact with each other via long-distance. However, such transient species have not been characterized sufficiently to understand correlation between the transient behaviours and interactions. In this project, we describe excited structure and dynamics in terms of coupling between the constituents on the basis of experimental results and theoretical calculations.
In a covalently linked copper(II) porphyrin-free base porphyrin dimer, the pathway of intramolecular energy transfer as well as its mechanism was studied by means of time-resolved EPR spectroscopy. Excitation wavelength dependence of TR-EPR signals also reveals characteristic relaxation in the energy acceptor, which is described as a weakly coupled triplet-doublet pair. Weak spin-spin interaction induces dynamics of the whole molecular system in the excited states.
In a series of rigidly-linked paramagnetic porphyrin-free base porphyrin dimers, intersystem crossing in the free base half is enhanced due to exchange interaction between the porphyrin electrons and unpaired electron in the paramagnetic metal. Spacer dependence study based on time-resolved fluorescence spectroscopy suggests through bond interaction between the two halves. An express for EISC was derived in terms of interaction between the unpaired electrons in the two halves.
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