Development of novel chromophores whose magnetic properties are controlled by photoexcitation

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In order to realize novel chromophores whose magnetic properties are controlled by photoexcitation, several chromophores linked to nitroxide radicals have been synthesized, and the magnetic properties after photoexcitation have been investigated. Followings are clarified.1. The interactions between the chromophores in the excited triplet state and nitroxide radical in the doublet ground state are systematically changed by synthesizing porphyrin or phthalocyanine complexes coordinated to nitroxide radical. The relationship between the bond number, distance, electron exchange interaction, lifetime, and electron spin polarization are clarified.2. Phthalocyaninatosilicons covalently linked to two nitroxide radicals have been investigated. In several microseconds, the magnetic properties in the ground state are controlled by photoexcitation, such as (thermal equillibrium)→(singlet)→(triplet)→(thermal equillibrium). These spin dynamics is reasonably interpreted by analyzing transient absorption and time-resolved EPR results.3. Light illumination effects on the magnetic properties of the crystal of phthalocyanine linked to one nitroxide radical have been studied. By the photoexcitation of Pc chromophore, the β spin of the nitroxide radical is efficiently changed to the α spin. That is, we have succeeded in controlling the magnetic properties of the paramagnetic crystal by photoexcitation.