Abstract: The electronic spectra and photo-physical behaviors of oxonol compound which is a cynine-like dye with negative charge in solution have been studied. It was found that evident difference was observed for the absorption spectra of this compound when it was dissolved in protic and in aprotic solvents respectively. It could be considered as the neutralization of this compound in non-polar solvent and the change of the whole molecular conjugation of oxonol. As compared with usual intra-molecular conjugated charge transfer compounds different behaviors were observed either for absorption spectrum or for fluorescence spectrum of this compound. All of these differences for spectra, especially the behavior of negative solvato-chromism in polar solvents, and the effect of pH value on the tautomerization of compound have been discussed in detail.

Key words: Oxonol dye, Negative solvatochromism, Molecular tautomerization, 　Electronic spectrum