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Pure Appl. Chem. Vol.
73, No. 3, pp. 519-523 (2001)
Pure and Applied
Vol. 73, Issue
Singlet and triplet energy splitting in the radical ion pairs generated
by photoinduced electron-transfer reactions*
Institute for Chemical Reaction Science, Tohoku University,
Sendai 980-8577, Japan
Abstract: Chemically induced dynamic electron polarization (CIDEP)
spectra generated by photoinduced electron-transfer reactions have been
studied using continuous-wave time-resolved EPR and FTEPR spectroscopy.
It has been suggested that the energy difference (DEST) between the
singlet and triplet states of radical ion pairs (RIPs) is dependent
on the charge recombination free energy (DGCR) and reorganization
energy (l). The result is interpreted in terms of the spin-selective
stabilization or destabilization of RIP states by electronic coupling
with the S0 and locally excited triplet states of the donoracceptor
pair at equilibrium distance in the reaction coordinate. It has been
verified that a charge transfer-type exchange interaction governs the
DEST. Magnitudes as well as the sign of DEST can be predicted at the
distance of the solvent-separated RIP based on DGCR and l values.
*Lecture presented at the XVIIIth IUPAC Symposium on
Photochemistry, Dresden, German , 22-27 July 2000.Other presentations
are published in this issue, pp.395-548.
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