Four Thermochromic o-Hydroxy Schiff Bases of α-Aminodiphenylmethane: Solution and Solid State Study

Abstract

More than a hundred years after the first studies of the photo- and thermochromism of o-hydroxy Schiff bases (imines), it is still an intriguing topic that fascinates several research groups around the world. The reasons for such behavior are still under investigation, and this work is a part of it. We report the solution-based and mechanochemical synthesis of four o-hydroxy imines derived from α-aminodiphenylmethane. The thermochromic properties were studied for the single crystal and polycrystalline samples of the imines. The supramolecular impact on the keto-enol tautomerism in the solid state was studied using SCXRD and NMR, while NMR spectroscopy was used for the solution state. All four imines are thermochromic, although the color changes of the single crystals are not as strong as of the polycrystalline samples. One of the imines shows negative thermochromism, and that one is in keto-amine tautomeric form, both in the solid state as in solution.

Keywords

• thermochromism
• Schiff base
• keto-enol tautomerism
• solution-based synthesis
• mechanosynthesis