Pulsed EPR and ENDOR Studies of Photochemical Reaction Dynamics of Transition Metal Complexes

脉冲EPR光谱比cw时间分辨EPR光谱具有更高的时间分辨率和灵敏度。我们已经尝试将这种强大的光谱学应用于研究金属配合物光化学反应的瞬态过程，如下所示。为了研究光化学反应，对国产电子自旋回波和自旋回波ENDOR仪进行了以下几点改进。(1)激光与微波脉冲同步运行和数据积累。(2)制备桥式环隙谐振腔，获得更高的时间分辨率和灵敏度。(3)制备高稳定的微波振荡器系统。(4)具有四个不同相位通道的微波脉冲发生器，可测量FT-EPR光谱。将所制备的脉冲EPR谱仪的效率与cw时间分辨EPR谱仪进行了比较，证实了脉冲方法具有更高的时间分辨和灵敏度，但将其应用于过渡金属离子中产生含自旋中心的顺磁性中间物质的反应体系的研究还存在一些问题。用分光计研究了下列光化学反应。(1)锌卟啉与醌之间的光诱导电子转移反应。(2)双（二乙基二硫代氨基甲酸）铜（II）及其配合物的光还原反应。(3)用时间分辨ENDOR方法研究卟啉光激三重态的超精细耦合相互作用。

The pulsed EPR spectroscopy has higher time resolution and sensitivity than CW-time resolved EPR spectroscopy. We have attempted to apply such a powerful spectroscopy to study of transient processes of photochemical reactions of metal complexes as the following.1. The home made electron spin echo and spin echo ENDOR instrument was modified on the following points so as to enable study of photochemical reactions. (1) Synchronous operation of laser light and microwave pulses and data accumulation. (2) Preparation of bridged loop gap resonator to get higher time resolution and sensitivity. (3) Preparation of highly stable microwave oscillator system. (4) Microwave pulse generator with four channels of different phases which enables measurements of FT-EPR spectra.2. Efficiency of the prepared pulsed EPR spectrometer was compared with that of the CW-time resolved EPR spectrometer and it was confirmed that the pulse method has much higher time resolution and sensitivity, but it has still some problems to apply it for studies of reaction systems which produces paramagnetic intermediate species containing spin centers in the transition metal ions.3. By using the spectrometer, the following photochemical reactions have been investigated. (1) Photoinduced electron transfer reactions between zinc porphyrins and quinones. (2) Photoreduction reaction of bis(diethyldithiocarbamato)copper(II) and its related complexes. (3) Hyperfine coupling interactions in the photoexcited triplet state of porphyrins by the time resolved ENDOR method.