Shape Permanence in Diarylethene-Functionalized Liquid-Crystal Elastomers Facilitated by Thiol-Anhydride Dynamic Chemistry

Diarylethene-functionalized liquid-crystalline elastomers (DAE-LCEs) containing thiol-anhydride bonds were prepared and shown to undergo reversible, reprogrammable photoinduced actuation. Upon exposure to UV light, a monodomain DAE-LCE generated 5.5 % strain. This photogenerated strain was demonstrated to be optically reversible over five cycles of alternating UV/Visible light exposure with minimal photochrome fatigue. The incorporation of thiol-anhydride dynamic bonds allowed for retention of actuated states. Further, re-programming of the nematic director was achieved by heating above the temperature for bond exchange to occur (70 °C) yet below the nematic-to-isotropic transition temperature (100 °C) such that order was maintained between mesogens. The observed thermal stability of each of the diarylethene isomers of over 72 h allowed for decoupling of photo-induced processes and polymer network effects, showing that both polymer relaxation and back-isomerization of the diarylethene contributed to LCE relaxation over a period of 12 hours after actuation unless bond exchange occurred.