Multistage and Multicolor Liquid Crystal Reflections using a Chiral Triptycene Photoswitchable Dopant

The photomodulation of the helical pitch of cholesteric liquid crystals (CLCs) results in dynamic and colored canvases that can potentially be used in applications ranging from energyefficient displays to color filters, anti-counterfeiting tags and LC lasers. The challenge in attaining these functions though is the development of photoswitchable chiral dopants with optimal properties that can modulate the CLCs in a controllable and multistage manner, to afford longlived multi-color reflections from the LC surface. Here we report on the structure property analysis of a series of photoswitchable chiral dopants that combine the large geometrical change and bistabilty of hydrazone switches with the efficient helical pitch induction of the new chiral motif, triptycene. These studies have elucidated the effects that conformational flexibility, dispersion forces, and - interactions have on the chirality transfer ability of the dopant. Finally, we used the best performing dopant in designing LC surfaces whose reflected wavelength (450-800 nm) can be controlled and tuned as a function of irradiation wavelength or time dependent isomer ratio. The bistability of the hydrazone switch allowed us to lock-in different reflected colors from the surface including the primary colors red, green, and blue, for extended periods of time. Finally, irradiation time with visible light (442 nm) combined with a simple digital light processing microscope projection setup was used in drawing numerous multi-colored images on an LC canvas, showcasing the fine control this dopant yields over the LC assembly. This work demonstrates how the combination of a bistable photoswitch with a chiral motif having a strong helical twisting power can result in adaptive LC surfaces whose properties can be tuned with exceptional efficiency.