Dynamic Photochromic Molecular Design for Regulating the Structure–Property–Function Relationship of Liquid Crystalline Polymer Networks

Abstract

The ability to simultaneously regulate optical response, mechanical properties, and macroscopic actuation remains a central challenge in the molecular design of photoresponsive liquid crystalline polymer networks. While photochromic molecules have been widely explored as optical switches, their dynamic structural evolution during polymerization and their influence on polymer network formation have received little attention. Herein, we demonstrate that a liquid-crystalline dithienylcyclopentene dye (Dye-LC-7) can function not merely as a photochromic chromophore but as a molecular regulator of the structure–property–function relationship in liquid crystalline networks. By integrating a mesogenic unit with a dithienylcyclopentene photochromic core, Dye-LC-7 undergoes reversible opening/ring-closed photoisomerization while maintaining excellent compatibility with the liquid crystalline host. Because UV-induced network formation occurs concurrently with photochromic conversion, the resulting polymer network contains coexexisting ring-open and ring-closed species dynamic equilibrium of ring-open and ring-closed species, enabling simultaneous regulation of molecular ordering, optical absorption, and network mechanics. Comprehensive optical, thermal, mechanical, and photomechanical characterizations demonstrate that Dye-LC-7 preserves liquid crystalline alignment, tunes the glass transition temperature and storage modulus in a concentration-dependent manner, and significantly enhances photoinduced bending while maintaining superior dimensional stability compared with conventional Disperse Red 1 (DR1)-containing systems. Furthermore, splay molecular alignment produces greater photomechanical deformation than planar alignment because the director gradient efficiently converts molecular photostrain into macroscopic bending. Collectively, these results reveal that the coexistence of photochromic molecular states, rather than either individual molecular state, governs the photomechanical behavior of liquid crystalline polymer networks. This work establishes a general molecular design principle for exploiting reversible photochromic switching to couple molecular organization, network mechanics, and light-driven actuation, offering new opportunities for adaptive photonic materials, intelligent soft actuators, and next-generation photoresponsive polymers.