title: Fluorinated Azobenzenes for Shape-Persistent Liquid Crystal Polymer Networks.
abstract: Liquid crystal polymer networks respond with an anisotropic deformation to a range of external stimuli. When doped with molecular photoswitches, these materials undergo complex shape modifications under illumination. As the deformations are reversed when irradiation stops, applications where the activated shape is required to have thermal stability have been precluded. Previous attempts to incorporate molecular switches into thermally stable photoisomers were unsuccessful at photogenerating macroscopic shapes that are retained over time. Herein, we show that to preserve photoactivated molecular deformation on the macroscopic scale, it is important not only to engineer the thermal stability of the photoswitch 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 their photochemical shape for more than eight days, which constitutes the first demonstration of long-lived photomechanical deformation in liquid-crystal polymer networks.
authors.affiliation: Bio-inspired and Smart Materials (BNT), University of Twente, 7500AE, Enschede, The Netherlands.
authors.forename: Supitchaya
authors.initials: S
authors.lastname: Iamsaard
authors.affiliation: Chemistry Research Laboratories, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Anger
authors.affiliation: Bio-inspired and Smart Materials (BNT), University of Twente, 7500AE, Enschede, The Netherlands.
authors.forename: Sarah Jane
authors.initials: SJ
authors.lastname: Aßhoff
authors.affiliation: Bio-inspired and Smart Materials (BNT), University of Twente, 7500AE, Enschede, The Netherlands.
authors.forename: Alexis
authors.initials: A
authors.lastname: Depauw
authors.affiliation: Chemistry Research Laboratories, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK. stephen.fletcher@chem.ox.ac.uk.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Fletcher
authors.affiliation: Bio-inspired and Smart Materials (BNT), University of Twente, 7500AE, Enschede, The Netherlands. n.h.katsonis@utwente.nl.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Katsonis
keywords: liquid crystals; molecular switches; photochromism; smart materials; soft actuators