Indication of ferroelectricity in columnar mesophases of pyramidic molecules

We have synthesized and studied trisbenzocyclononenes carrying six chiral side chains. They are pyramidic shaped molecules exhibiting columnar mesophases. The optical and electro-optical effects of this chiral pyramidic compound have been studied. A homeotropic alignment of the columnar phase was achieved by cooling the film between plates treated with octadecyltriethoxysilane in the presence of a d.c. field. A transient optical effect was observed with these films on electric field reversal. Simultaneously there was a peak in the time dependence of the electric current flowing through the sample. The observations indicate that the columnar phase is ferroelectric with the polarization parallel to the optical axis. A few degrees below the clearing point, the time for polarization reversal is in the range of seconds and the magnitude of the polarization is 10 mC m(-2). An electroclinic effect was observed for films with fan textures.