The nature of the long-wave bands in the emission spectra of aromatic o-hydroxycarboxylic acids and their derivatives

The reasons for the simultaneous presence of two emission bands, blue and red, in the fluorescence spectra of certain aromatic o-hydroxycarboxylic acids and their derivatives have been examined. It was shown that the unusual luminescence properties of these compounds were determined by the large differences in energy of the intramolecular hydrogen bonds in the normal and excited electronic states. The long-wave luminescence bands in similar cases are the result of optical transitions in the high frequency sublevels of the ground electronic state (sometimes in the dissociaton region of the hydrogen bond).