Photo-Induced Spin Alignment Using Photo-Excited High-Spin State of π-Conjugated Stable Radicals

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This project was carried out in order to clarify the electronic structure and the dominant mechanism of the spin alignment in the photo-excited states of π-conjugated organic multi-spin systems. The following new findings were obtained through this project.(1)According to the proposal, we make up the transient absorption spectroscopy apparatus as well as the time-resolved fluorescence measurement system attached with variable temperature system. The life-times of the photo-excited high-spin organic systems were determined to be ca. 10-20 μs at 77 K using this apparatus.(2)The photo-excited quartet and quintet high-spin states of the verdazyl radical systems have been first detected. The photo-excited quartet high-spin state was also detected for the pyrene-verdazyl radical. Based on these results, the necessary conditions to obtain the photo-excited high-spin state have been clarified in detail and succeeded to establish the guiding principles for the molecular designing of organic spi … More n system with the high-spin photo-excited state.(3)The role of π-topology in the spin alignment on the photo-excited state has been proven by studying the photo-excited states of π-conjugated Anthracene-t-Butyl-Nitroxide radicals.(4)A unique lowest triplet photo-excited state constructed from four unpaired electrons was detected for the first time by the proper molecular design taking π-topology into account. The magnitude of the fine-structure parameters is reduced by the antiferromagnetic intramolecular spin alignment.(5)The stable radicals with photo-excited high-spin states, which electron donor property was improved by attaching dimethylamino group were synthesized and their electronic states and physical properties were investigated. One of the problems was solved, which are concerned with the construction of the charge-transfer complexes using the π-conjugated organic spin systems with the photo-excited high-spin states.(6)In order to investigate the possibility of LIESST using organic spin systems, we synthesized several charge-transfer complexes constructed from the π-conjugated organic spin systems with the photo-excited high-spin states and the proper electron accepters. Their basic physical and optical properties as well as the electronic structures were clarified by ESR, time-resolved ESR, optical absorption, and SQUID measurements. Less