Polarity-sensitive switching induced by the electric field in a self-assembled nematic system from two different achiral species of molecules

A polarity-sensitive switching behavior was observed in the nematic phase of a system of unit blocks self-assembled from an achiral rod-shaped liquid crystal (LC) and an achiral tripod-shaped dopant. This unit block has a shape of a tripod with extended legs and showed a spontaneous polarization under the applied electric field. Although the polarity-sensitive switching in the achiral LCs is intrinsically impossible, our system of the tripod-shaped unit blocks made with the linear-shaped achiral 8CB bound to the stretched branches of the tripod-shaped achiral dopant by the steric interaction or by the hydrogen bonding showed the polarity-sensitive switching. At zero applied field state, the unit blocks were aligned helically to compensate the macroscopic polarization value. As the field was applied, the helical structure was unwound and the optic axis of the sample rotated clockwise or counterclockwise depending on the sign of the applied field. The threshold field to show the polarity-sensitive switching was lower in the sterically assembled sample (0.1V/μm) than in the hydrogen-bonded one (1.3V/μm) and the field response time was much faster in the former case. In addition, the response time of the sterically assembled sample was linearly proportional to the strength of the electric field in the strong field regime, but the one of the hydrogen-bonded sample was saturated in the strong field regime.