CONSTRUCTION OF A SPIN-STATE-SWITCHING MOLECULAR SYSTEM BY USING STRUCTURAL CHANGE OF ELECTROCHROMIC MOLECULES

为了实现自旋态开关分子系统，我们在量子化学计算的基础上设计了合适的分子系统。此外，我们还制备了模型分子的前驱体，并对前驱体氧化后产生的阳离子自由基的磁性进行了研究。此外，我们还合成了几种芳胺，并利用电子自旋共振（ESR）方法研究了它们阳离子自由基的自旋电子态。这些阳离子自由基被发现是有用的自旋态开关分子体系的自旋承载单元。结合已有的结果，我们制备了携带两个氮氧自由基的四芳基乙烯。所得到的化合物是顺式异构体和陷阱异构体的混合物，因此该分子的ESR谱可以解释为两种自旋三重态的混合物。磁化率测量结果表明，两种氮氧化物自由基之间存在很强的分子内磁相互作用。电化学研究表明，该分子的构型是由于双电子氧化后烯烃键的延长而产生的扭曲构象。结果表明，该化合物的ESR谱显示出由独立的一氧化二氮自由基组成的超精细结构谱。这一结果表明，两种氮氧化物自由基之间不存在分子内磁相互作用。进一步证实，通过适当的还原剂处理，该分子的中性态可以从指示态恢复。因此，我们可以展示自旋态开关分子系统的一个典型例子。

In order to realize a spin-state-switching molecular system, we have designed suitable molecular systems on the basis of quantum chemical calculations. Moreover, we have prepared the precursors of model molecules, and then have examined the magnetic properties of the cation radicals which are generated after oxidation the precursors.In addition, we have synthesized several arylamines and have examined the spin electronic states of their cation radicals by using the electron spin resonance (ESR) method. These cation radicals were found to be useful for spin-bearing units of spin-state-switching molecular systems. Considering the results obtained, we have prepared the tetraarylethylene carrying two nitroxide radicals. The resulting compound is a mixture of cis- and traps- isomers, and therefore the ESR spectrum of this molecule can be explained to be a mixture of two kinds of spin-triplet species. As a result of the magnetic susceptibility measurements, a strong intramolecular magnetic interaction exists between the two nitroxide radicals. The electrochemical studies revealed that the dication of this molecule takes a distorted conformation originating from lengthening of the olefinic bond after two-electron oxidation. Actually, the ESR spectrum of the dication showed a hyperfine-structured spectrum consisting of independent mononitroxide radicals. This result indicates that no intramolecular magnetic interaction exists between the two nitroxide radicals.Furthermore, it was confirmed that the neutral state of this molecule can be retrieved from the dication state by treating with a suitable reducing agent. Hence we could show a typical example of the spin-state-switching molecular systems.