Orthogonal photochemistry toward spatial reprogramming of 3D-printed liquid crystal elastomers

The versatile actuation of liquid crystal elastomers (LCEs), crucial for future soft robots, is determined by both geometrical shape and mesogen alignment. 3D printing can effectively manufacture complex shapes of LCEs, yet the precise reprogramming of mesogen alignment remains beyond control. To address this challenge, we report an orthogonal photochemistry design to decouple 3D printing and mesogen alignment. The former is achieved through visible light-triggered radical polymerization, whereas the latter can be accomplished via UV irradiation. While seeking suitable UV-sensitive chemistries compatible with traditional photocurable 3D printing, we demonstrate that the hexaarylbiimidazole structure is capable of dynamic bond exchange upon UV exposure. This remarkable UV responsive dynamic feature enables the programming, erasing, and multiple reprogramming of mesogen alignments for a 3D printed LCE in a spatio-temporal manner. The underlying strategy enables the realization of LCEs with arbitrary reprogrammable actuation, enriching the design strategies for future soft robots.