Evidence of a polar cybotactic smectic A phase in a new fluorine substituted bent-core compound

The mesomorphic properties of an achiral, fluorine substituted bent-core liquid crystal have been investigated using polarising optical microscopy, electro-optics, X-ray diffraction and dielectric spectroscopy. A new phase, designated as CybAP(A), has been found. This phase is a cluster phase consisting of microscopic enlarged antiferroelectric smectic A type clusters. The CybAP(A) phase is observed below a SmA phase and exists irrespective of the alignment layer and the cell thickness. The CybAP(A) phase behaves like a nematic phase with low viscosity and exhibits thermal fluctuations. But on applying an electric field, it shows smectic-like textures and exhibits tristable antiferroelectric switching. X-Ray diffraction of aligned samples of this phase confirms the non-tilted orientation of the major director and long range 1D positional order of the molecules. The dielectric spectroscopic studies show the appearance of strong dipolar correlations on approaching the CybAP(A) phase from the higher temperature SmA phase, confirming the formation of SmAP(A) clusters, which is associated with the onset of phase biaxiality. This provides a significant step forward to achieve the illusive orthorhombic biaxial cybotactic nematic phase from bent-core molecules.