Chromic Schiff Bases: Transformative Stimuli-Responsive Systems for Next-Generation Soft Materials

Abstract

Stimuli-responsive systems, which are often hailed as "smart" materials, have garnered significant attraction over the recent decades due to their remarkable dynamic reactivity towards numerous external triggers. Among these, Schiff bases owing to the presence of distinctive imine group (C=N), formed through a condensation reaction between an aldehyde or ketone and a primary amine, have become especially captivating. In addition to offering a cost-effective and easily accessible synthesis, these Schiff bases can also demonstrate extraordinary chromic properties. On providing various triggers such as mechanical stress (mechanochromism), temperature variations (thermochromism), solvent change (solvatochromism), and pressure (piezochromism), Schiff bases show vivid colour changes thus demonstrating their remarkable versatility. These chromic shifts can be attributed to reversible modifications in molecular conformation, electronic states, and intermolecular interactions within the Schiff base framework. The intrinsic ability of Schiff bases to respond and adapt to environmental changes makes them compelling candidates for the development of next-generation soft materials, with applications ranging from high-sensitivity sensors and adaptive displays to self-healing materials. Their multi-stimuli responsive behaviour opens up pathways for innovations in self-healing coatings, where damaged materials can autonomously repair themselves upon exposure to heat or pressure. This review dives deeply into the intricate mechanisms responsible for their stimuli-responsive behavior and presents a futuristic approach to enhance their performance, highlighting them at the forefront of future stimuli-responsive and self-healing technologies.