Formation of a Complete Electron Transfer State of 9,9'-Bianthryl in a Polar Solvent

K. Nishiyamaa, T. Hondab and T. Okadab a Venture Business Laboratory, Osaka University, Suita, Osaka 565-0871, Japan b Department of Chemistry, Graduate School of Engineering Science, Osaka, University Toyonaka, Osaka 560-8531, Japan

Received: July 23, 1998; in final form September 14, 1998

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It has been generally recognized that excited 9,9'-bianthryl in polar solvents achieves a partial charge-separation state, instead of a complete electron transfer state, even in high-polarity solvents like acetonitrile at room temperature. However, here we firstly found that 9,9'-bianthryl reaches the complete electron transfer state in a polar alkanenitrile solvent at lower temperature as elucidated by means of transient absorption and steady-state fluorescence spectroscopy. A stepwise increase in the fluorescence Stokes shift observed when temperature was reduced implies a formation of a state more polar than that dominated at the room temperature. At low temperature (165 K), the transient absorption spectra of 9,9'-bianthryl in butyronitrile gradually changed from the spectrum ascribed to the partial change-separation state toward that of the complete electron transfer state. We suggest that at low temperature, due to the increase in the solvent polarity, the energetically stabilized electron transfer state should be predominant.

DOI: 10.12693/APhysPolA.94.847 PACS numbers: 82.40.Js, 82.50.Fv, 0.5.40.+j, 71.35.Lk