Abstract
We report solvatochromic shift of the absorption spectrum and fluorescent red-edge effect (REE) of a betaine
molecule, 2-(1-pyridinio)benzimidazolate (SBPa) in saccharide glasses. Interestingly, SBPa exhibits REE
even in aqueous solution, where the microscopic environmental inhomogeneity is normally averaged over
time by the solvent thermal fluctuation. We conclude that SBPa exists in an equilibrium state between
betaine and protonated form in aqueous solution. Thus, frequency shift of absorption and fluorescence
spectra of SBPa could be not only a measure of solvent polarity but also that of solvent acidity, and the data
are reanalyzed by the new knowledge. Nevertheless, Stokes shift of SBPa in trehalose glass is the smallest
compared to other saccharide glasses measured in this study, indicating significant suppression of molecular
fluctuation by trehalose glass.
