Photochemically formed contact radical pair and its unusual spin polarization

本项目的目的是利用光导检测磁共振（PCDMR）和瞬态吸收检测磁共振（ADMR）的新检测技术，阐明光化学反应中瞬时形成的自由基离子对和接触自由基对的动力学。1996：用PCDMR和ADMR方法研究了TMPD在醇中通过自由基-离子对的光离过程。将之前脱氧的样品溶液在ESR腔中进行光解，利用强微波功率监测ESR条件下的电导率变化。我们终于成功地观察到了瞬态自由基-离子对。这是国际上首次用PCDMR方法观察自由基离子对的报道。在ESR条件下对瞬态吸收（光学）的观测证明了PCDMR光谱是对真实自由基离子对的观测。谱变宽的主要原因可能是自由基-离子对的动力学性质的改变，而短寿命的接触自由基对的形成是导致谱变宽的主要原因。并进行了理论分析。1997年：我们利用PCDMR技术研究了一个光诱导电子转移反应体系。以山酮和N，N-二乙基苯胺在2-丙醇中的脱氧溶液为样品。已知该系统显示出与均匀条件相反的大的外磁场效应。最后，我们成功地观察了由山酮阴离子和二乙基苯胺阳离子自由基组成的自由基-离子对的PCDMR光谱。我们还成功地确定了自由基-离子对的寿命约为200ns。与2-丙醇在相同条件下的普通自由基对相比，这是非常长的。这种长寿命是造成大的外磁场效应的主要原因。这种长寿命可能是由于自由基离子对和醇分子之间形成的网络。在很强的微波辐射下，谱线显示出ESR的禁跃迁。这意味着两个自由基离子是波动的，它们经常在近距离相遇，如接触自由基对。少

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