Photoresponsive ionic liquid crystals

Photoresponsive ionic liquid crystals (PILCs) emerge as a captivating class of materials, seamlessly merging the distinct properties of ionic liquids, liquid crystals, and photoresponsive groups. This innovative combination empowers PILCs to exhibit remarkable phase transitions and responsiveness to external stimuli, particularly light and temperature. In this review, we have detailed various kind of PILCs reported to date. PILCs are further categorized based on their molecular composition. One-component PILCs are composed of a single component having ionic, photoresponsive and mesogenic groups. They are further subdivided into monomeric, oligomeric, and polymeric one-component PILCs. Monomeric PILCs exhibit lyotropic (concentration-dependent) and thermotropic (temperature-dependent) structural changes in response to external stimuli. Oligomeric PILCs, with multiple photoresponsive units, offer precise control over self-assembly and phase behavior. Polymeric PILCs feature a polymeric cationic backbone with attached anionic photochromic groups. Furthermore, two-component PILCs consist of two distinct components consisting of varying combination of ionic, photoresponsive and mesogenic groups. Similarly, three-component systems consist of three distinct components of similar varying combination as discussed above. All these materials enable precise control of phase transitions and structural properties through light stimuli, opening up exciting possibilities for future innovations in optoelectronic devices, smart sensors, and light-controlled systems. © 2024 Elsevier B.V.