Molecular frustration of chemically linked rod-disc liquid crystal under an electric field

Molecular orientation of a chemically linked rod-disk (cyanobiphenyl- triphenyl) liquid crystalline (LC) molecule (RD12, where 12 is a number of carbon atoms in each alkyl chain linkage between the rod and the disk mesogens) in an antiparallel rubbed LC cell was investigated under vertically applied alternative current (AC) electric fields. Upon varying vertical AC electric fields from the initial state (0 V) to a fixed voltage ranging between 2.5 and 5.0 V, it was found that RD12 responded to the electric field with two-steps. The rod mesogen having a higher dipole interaction first aligned parallel to the electric field, while the disk mesogen behaved like an anchor of RD12. After the frustration and stabilization of rod mesogens, the in-plane axis of disk mesogen also aligned parallel to the electric field. Based on our experimental results, it was concluded that the peculiar molecular frustrations of RD12 under the vertical AC electric field occurred in a consequence of the competition among rods attached to both sides of the disk molecule. Furthermore, because molecular orientation of RD12 exhibiting a large birefringence is controlled by an electric field, RD12 can be used as a tunable optical switching material in the electro-optical devices.