Photo-Induced Stepwise Liquid Crystal Phase Transition Enabled by Hydrazone Photoswitch

Advanced liquid crystal (LC) materials with photo-induced phase transition behaviors hold significant scientific and technological importance because of its potentials in next-generation optoelectronic devices and information encryption. Azobenzene-based LC has been widely studied in this field for several decades. However, the relatively poor thermal stability of the cis isomer of azobenzene severely limits its applications in state-locking and high-temperature scenarios. Herein, a photoisomerizable and bistable hydrazone molecule was judiciously designed and synthesized. The hydrazone photoswitch undergoes linear-to-bent configurational changes via light-driven isomerization, achieving isothermal and reversible control of LCs from ordered to disordered states. The perturbation effects of hydrazone isomerization on LC phase were analyzed by measuring the dichroism ratio (R) and order parameter (S_Φ). Thanks to the bistability of hydrazone molecules, the phase transition temperatures of the LCs can be precisely and stepwise controlled by regulating light intensity and exposure time. Utilizing the unique light-induced phase transition of hydrazone-doped cholesteric liquid crystals (CLCs), thermoresponsive colorful optical devices with reversibly writable and erasable patterns by light were demonstrated, highlighting their significant potential for applications in smart optical materials.