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

为了实现自旋态转换的分子体系，我们在量子化学计算的基础上设计了合适的分子体系。此外，我们还制备了模型分子的前驱体，然后研究了前驱体氧化后生成的阳离子自由基的磁性。此外，我们还合成了几种芳胺类化合物，并用电子自旋共振(ESR)方法研究了它们的阳离子自由基的自旋电子态。这些阳离子自由基被发现对自旋-状态转换分子系统的自旋单元是有用的。考虑到所得到的结果，我们制备了带有两个氮氧自由基的四芳基乙烯。得到的化合物是顺式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。磁化率测量的结果是，两个氮氧自由基之间存在着很强的分子内磁性相互作用。电化学研究表明，该分子的阳离子具有扭曲的构象，这是由于两电子氧化后烯键的延长所致。实际上，产物的ESR谱显示了由独立的一氮氧自由基组成的超精细结构光谱。这一结果表明，两个氮氧自由基之间不存在分子内磁相互作用，并且证实了通过合适的还原剂处理，该分子可以从定性态恢复到中性状态。因此，我们可以给出一个自旋态开关分子系统的典型例子。

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.