Low transition temperature organosiloxane liquid crystals displaying a de Vries smectic A phase

The synthesis, phase properties and electro-optic response of two new chiral low molar mass organosiloxane liquid crystalline materials are presented. The structure of the molecule contains a short (three silicon atoms) siloxy chain attached via a hydrocarbon chain to the non-chiral end of a chiral mesogenic moiety. The materials have low melting points (> -20°C) and broad smectic phase ranges (∼80°C wide) extending to below room temperature. Both materials are electroclinic at room temperature. A 30° tilt of the optic axis can be achieved in fields of the order of 25 V μm^-1. The data presented indicate that in these materials the smectic phase is a de Vries-type smectic A phase. The electroclinic effect arises because the electric field produces a bias in the distribution of the direction of the tilt.