Pseudopolar smectic-C phases of azo-substituted achiral bent-core hockey-stick-shaped molecules

We report experimental studies on an azo-substituted compound consisting of bent-core hockey-stick-shaped molecules. The experimental results establish two pseudopolar tilted smectic phases, which are characterized by an in-plane axial-vector order parameter in addition to tilt order in the smectic layers. Electro-optical measurements in the mesophases indicate that the birefringence of the sample strongly depends on the applied electric field. We develop a theoretical model to account for this observation. The change in the birefringence of the sample arises from the field-induced reorientation of the tilt plane of the molecules in the layer above a threshold field. The effect is analogous to the field-induced Freedericksz transition which is quadratic in the applied electric field.