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

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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.