A new series of chiral nematic bimesogens for the flexoelectro-optic effect

A series of chiral bimesogenic compounds has been synthesized. The molecules comprise beta-estradiol as the central chiral unit, which is attached to a terminal 4'-cyanobiphenyl-4-yl group at C-17 by an alkanoate spacer containing 5, 6 or 11 carbon atoms. At C-3 the estradiol moiety is substituted with an omega-alkenyloxy chain, also containing 5, 6 or 11 carbon atoms. We will describe the synthesis and phase characterization of these materials. The compounds with 5 or 11 carbon atoms in the spacer separating the mesogens display chiral nematic mesophases with temperature ranges up to 40 ° C, entering the isotropic state at about 100 ° C. The pitch lengths of these pure materials are remarkably invariant with temperature. Their electro-optic behaviour has been characterized, with particular emphasis on their flexoelectric properties. The materials have the highest flexoelectric coefficients reported so far in any chiral nematic liquid crystal [with e (kappa-1) < + 0.5 C N -1 m -1], with flexoelectro-optic response times, for 0 to 90% of transmitted intensity, of the order or less than 1 ms.