Photochemically formed contact radical pair and its unusual spin polarization

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The aim of this project is to clarify the dynamics of the radical-ion pairs and contact radical pairs formed transiently in photochemical reactions using new detection techniques of a photoconductivity detected magnetic resonance (PCDMR) and a transient absorption detected magnetic resonance (ADMR).1996 : The photoionization process of TMPD in alcohol by way of the radical-ion pair was investigated by PCDMR and ADMR methods. The sample solutions previously deoxygenated were photolyzed in the ESR cavity, and the conductivity change was monitored under the ESR conditions by applying strong microwave power. We finally succeeded in the observation of the transient radical-ion pair. This was the first report of the observation of the radical-ion pair using PCDMR method in the world. The trial of the observation of the transient absorption (optical) under ESR conditions proved that the PCDMR spectrum was the observation of the real radical-ion pair. The spectrum was broadened probably due to … More the dynamic properties of the radical-ion pair, and the formation of the contact radical pair having short lifetime was the main cause of the broadening. Theoretical analysis was also performed.1997 : We investigated a system of the photoinduced electron transfer reaction using the PCDMR technique. The deoxygenated solution of xanthone and N,N-diethylaniline in 2-propanol was used as the sample. This system is known to show large external magnetic field effect contrary to its homogeneous conditions. Finally, we succeeded in observing the PCDMR spectrum of the radical-ion pair composed of xanthone anion and diethylaniline cation radicals. We also succeeded in determining the lifetime of the radical-ion pair to be about 200 ns. That is extremely long comparing with the ordinary radical pair in 2-propanol under the same conditions. This long lifetime is the main cause of the large external magnetic field effect. This Iong lifetime may be due to the network formation between the radical-ion pair and alcohol molecules. The spectrum showed a forbidden transition of ESR under very strong microwave radiation. This implies that two radical ions are fluctuating and frequently they encounter in close distance such as the contact radical pair. Less