Tuning the Properties\nof Hydrazone/Isosorbide-Based\nSwitchable Chiral Dopants

The long-range supramolecular interactions in liquid\ncrystals (LCs)\ncan be used to amplify and subsequently propagate microscopic structural\nchanges into macroscopic events. Here, we report on a systematic structure–property\nanalysis using 16 chiral photoswitchable dopants composed of bistable\nhydrazones and chiral isosorbide moieties. Our findings showcase the\nrelationship between the dopant’s structure and its helical\ntwisting power (β), and hence, the photophysical properties\nof the host LC. We show that an increase in the hydrazone CNNH dihedral\nangle results in an increase in the β value, while alkoxy chains\ndo not lead to such an increase. These results contradict established\nrules of thumb, stating that structural rigidity and long alky chains\nare needed for high β values. We also found that the position\nof the substitution, whether at the 2′ or 5′ positions\nof the isosorbide unit, or the attachment of the chiral unit to the\nrotor or stator phenyl units can have negative or positive additive\neffects that can either increase or decrease the β values. These\nresults made us hypothesize that unsymmetrically functionalized dopants\nshould result in large Δβ values, which we corroborated\nexperimentally. Moreover, a fluorine-functionalized dopant resulted\nin higher overall β values, most likely because of π–π\ninteractions. Finally, the dopants were used in modulating and locking\nin the reflective properties of LC films, yielding multicolor LC canvases\nthat can reflect light from the ultraviolet to the infrared range\n(i.e., a manipulation of up to ca. 1500 nm of reflected light).