Halogen-Bonded Liquid Crystal Elastomers as Initiator-Free Photochemical Actuators

Photochemically driven liquid crystal elastomer (LCE) actuators require precise arrangement and sufficiently high concentration of photoswitchable molecules for effective actuation. Achieving both high photoswitch content and a high degree of molecular alignment has been challenging especially in thick samples, but is essential for future applications in soft robotics, biomedicine, and photonic technologies. In this work, this issue is addressed by combining dynamic halogen bonds with Aza-Michael addition-based polymerization, creating azobenzene-containing LCEs with multimodal actuation capabilities. These highly directional supramolecular interactions eliminate the need for a photo-initiator in the LCE fabrication process, enabling control over the azobenzene content over a wide range while maintaining a high degree of molecular alignment and dynamic programming ability. The potential of this approach is demonstrated through proof-of-concept examples such as light-guided rolling movement and underwater gripping, underscoring the versatility of the weak, dynamic halogen bonds in advancing the supramolecular design of multimodal soft actuators.