Fluorinated azobenzenes for shape-persistent liquid crystal polymer networks

Liquid crystal polymer networks respond with anisotropic deformation to a range of external stimuli. When doped with molecular photo-switches, these networks undergo complex shape modification under illumination. As the deformations reverse when irradiation stops, applications where thermal stability of the activated shape is required were precluded. Previous attempts to incorporate molecular switches with thermally stable photo-isomers were unsuccessful at photo-generating macroscopic shapes that are retained in time. Here, we show that the key to preserving photo-activated molecular deformation on the macroscopic scale is not only to engineer the thermal stability of the photo-switch but also to adjust the cross-linking density in the polymer network and to optimize the molecular orientations in the material. Our strategy resulted in materials containing fluorinated azobenzenes that retain photochemical shape morphing for more than eight days, which constitutes the first demonstration of long-lived photomechanical deformation in liquid crystal polymer networks

High-Power Actuation from Molecular Photoswitches in Enantiomerically Paired Soft Springs

Motion in plants often relies on dynamic helical systems as seen in coiling tendrils, spasmoneme springs, and the opening of chiral seedpods. Developing nanotechnology that would allow molecular-level phenomena to drive such movements in artificial systems remains a scientific challenge. Herein, we describe a soft device that uses nanoscale information to mimic seedpod opening. The system exploits a fundamental mechanism of stimuli-responsive deformation in plants, namely that inflexible elements with specific orientations are integrated into a stimuli-responsive matrix. The device is operated by isomerization of a light-responsive molecular switch that drives the twisting of strips of liquid-crystal elastomers. The strips twist in opposite directions and work against each other until the pod pops open from stress. This mechanism allows the photoisomerization of molecular switches to stimulate rapid shape changes at the macroscale and thus to maximize actuation power