Surface-driven switching of liquid crystals using redox-active groups on electrodes.

Electrochemical control of the oxidation state of ferrocene-decorated electrodes leads to surface-driven changes in the orientations of thermotropic liquid crystals. When the electrodes possess nanometer-scale topography, voltages of 0.0 to 0.3 volts (versus a counter electrode in a two-electrode cell) can drive changes in the orientation of the liquid crystals in the plane and/or out of the plane of the electrodes. Electrodes not supporting ferrocene do not lead to surface-driven orientational transitions. The in-plane transitions are driven by the reorganization of the monolayer of ferrocene upon oxidation of ferrocene to ferrocenium. The out-of-plane transition reflects a dielectric coupling between the liquid crystal and the diffuse part of an electrical double layer that evolves upon oxidation of ferrocene to ferrocenium. These results suggest new ways to couple the orientations of liquid crystals to chemical and electrical stimuli in electro-optical devices and chemical sensors.