Structure and Physicochemical Properties of Three Structural Forms of Organic Luminophore 2-((2-Benzo[d]thiazol-2-yl)phenyl)carbamoyl)benzoic Acid

It has been established by single-crystal X-ray diffraction (XRD), differential scanning calorimetry, and luminescence spectroscopy that the color differences in the fluorescence of a 2-((2-(benzo[d]thiazol-2-yl)phenyl)carbamoyl)benzoic acid (I) luminophore is caused by the existence of its three structural forms, two of which are different crystalline modifications and one is amorphous. Under the UV irradiation, green, yellow, and orange glow of the compound is observed. The transition from the form with green glow to the form with yellow glow, as well as from the form with yellow glow to the form with orange glow, is a melt–crystal2 type phase transition rather than a crystal–crystal phase transition. In crystal structures, the intramolecular hydrogen bond weakens under the action of the intermolecular hydrogen bond. The stronger the newly formed bond, the weaker the intramolecular hydrogen bond is. The weakening of the intramolecular hydrogen bond is consistent with the red shift of the luminophore emission band.