New Schiff base salts as sources of blue and green light in the solid state: the role of the anion and protonation

Abstract

A new polymorf of Schiff base (N-(4′-methoxybenzylidene)-4-aminobenzoic acid) and five of its distinct salts (chloride, bromide, nitrate, hydrosulfate and dihydrophosphate) were designed and synthesized. Detailed examinations were conducted to determine the structure and spectral properties of these compounds, employing methods like X-ray diffraction, as well as IR, UV-Vis and fluorescence spectroscopy. Interestingly, all the synthesized Schiff base salts displayed fluorescence when in solid state. However, the intensity of this fluorescence was found to differ, depending on the type of anion present within the structure. This result provides evidence that a strategy similar to supramolecular complexation can effectively be used to adjust the emission wavelength and control the intensity of fluorescence in the resulting solid materials.