Photoinduced Reversible Deformations of Azobenzene-Based Main-Chain Liquid Crystalline Polymer Films

Recently, photodeformable liquid crystalline polymer materials (LCPMs) have attracted tremendous attention owing to their fascinating photoresponsive properties and promising applications. However, conventional photodeformable LCPMs invariably depend on mesogenic alignment and irreversible crosslinking, which conflate structural order with chemical irreversibility and leave no window for post-curing manipulation. To overcome this fundamental limitation, an azobenzene-containing main-chain LCP was synthesized via stepwise polymerization, and free-standing films were subsequently prepared by a simple drop-coating method, without any pre-alignment or crosslinking steps during film formation. Upon 365 nm ultraviolet (UV) irradiation (110 mW cm−2), azobenzenes in the LCP undergo trans-to-cis isomerization, resulting in a significant decrease in the storage modulus (G′). Subsequent 530 nm green light exposure (110 mW cm−2) induces the reverse cis-to-trans isomerization, leading to an increase in G′. Furthermore, LCP films exhibit rapid and reversible deformations upon alternating exposure to 365 nm (110 mW cm−2) and 530 nm (110 mW cm−2) light, with a bending-flattening cycle completed within 50 s. This strategy offers a simple and general route to polydomain, non-oriented free-standing LCP films capable of reversible photoactuation, showing promise for soft actuators and light-driven devices.