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Publications (2)3.6 Total impact

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    ABSTRACT: In high-spin chemistry, random-orientation fine-structure (FS) electron spin resonance (ESR) spectroscopy entertains advantages as the most facile and convenient method to identify high-spin systems, as frequently reported in the literature. Random-orientation ESR spectroscopy applicable to organic high-spin entities can date back to the Wasserman and co-workers' attempt on the first spin-quintet dicarbene, m-phenylenebis(phenylmethlene) (m-PBPM), in the 2-MTHF glass in 1963 and 1967, following their successful work on randomly oriented triplet-state ESR spectroscopy. The FS ESR spectrum of m-PBPM in the 2-MTHF glass, however, has never fully been analyzed due to a peculiar line-broadening appearing at many canonical peaks. Organic high-spin spectra from most quintet dinitrenes also suffer from similar phenomena. Seemingly intrinsic line-diffusing or -broadening phenomena adversely affect the reliable determination of FS parameters for organic high-spin entities in rigid glasses. In high-spin chemistry, the line-broadening has been an obstacle that masks key FS transitions in many cases. Thus, both the origin of the broadening and the comprehensive spectral analysis have been a long-standing issue. In this report, we examine the origin of the line-broadening appearing in the FS ESR spectra, illustrated by a comprehensive spectral analysis for m-PBPM in the quintet ground state and the first-documented quintet-state dinitrene, m-phenylenebis(nitrene) (m-PBN) in the 2-MTHF glass. A complete analysis of the random-orientation FS spectra from m-PBPM diluted in the benzophenone crystal has shown that the g-anisotropy of m-PBPM is not prominent. Also the higher-order FS terms such as S(i)(2)S(j)(2) group-theoretically allowed for S = 2 are not necessary in spite of the argument for a hydrocarbon-based tetraradical (S = 2) in the ground state. Our new approach to the line-broadening analysis invokes both exact analytical solutions for the resonance fields of canonical peaks and the magnetic-parameters gradient method. The D- and E-values of m-PBPM acquired by the spectral simulation in this study give different molecular structures of the quintet dicarbene in the benzophenone crystal lattice (D = +0.0703(0) cm(-1), E = +0.0212(0) cm(-1)) and in the 2-MTHF glass (D = +0.0780(0) cm(-1), E = +0.0221(0) cm(-1)). Microscopic origins of the line-broadening observed for high-spin oligocarbenes or oligonitrenes generated by photolysis in organic glasses have been proposed.
    The Journal of Physical Chemistry A 09/2009; 113(34):9521-6. · 2.77 Impact Factor
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    ABSTRACT: In high-spin chemistry, random-orientation fine-structure electron paramagnetic resonance (FS ESR) spectroscopy holds the advantages of the most facile and convenient method to identify high-spin systems. The FS ESR spectroscopy for high spins in frozen rigid glasses has seemingly been well established since the first spin-quintet m-dicarbene and m-dinitrene appeared in 1967. The FS ESR spectra of organic quintet entities generated by photolysis in the 2-methyltetrahydrofuran (2-MTHF) glass, however, have never been fully analyzed due to a peculiar line broadening appearing at many canonical peaks. The line broadening has been a notorious obstacle that masks key FS transitions of many cases in organic glasses or argon matrices. We examine the origin of the line broadening, illustrating the comprehensive spectral analysis for m-dinitrenes and other types of typical quintet-state dinitrenes observed in the 2-MTHF glass. Our new approach to the line broadening analysis invokes both exact analytical solutions for the resonance fields of canonical peaks and a magnetic-parameter gradient method. We have derived the exact analytical expressions for FS canonical peaks for high-spin states, for the first time. A microscopic origin of the line broadening observed for high-spin nitrenes generated by photolysis in rigid glasses is proposed on the basis of quantum chemical calculations of the D-tensor.
    Applied Magnetic Resonance 37(1):703-736. · 0.83 Impact Factor