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

Abstract

A series of chiral bimesogenic compounds has been synthesized. The molecules comprise b-estradiol as the central chiral unit, which is attached to a terminal 4¾ -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 v-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 40ß C, entering the isotropic state at about 100ß 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 exoelectric properties. The materials have the highest¯exoelectric coe cients reported so far in any chiral nematic liquid crystal [with e (kÕ 1 )> +0.5 C NÕ 1 mÕ 1 ], with¯exoelectro-optic response times, for 0 to 90% of transmitted intensity, of the order or less than 1 ms.

Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

“…21, 22 and 34-42)-we undertook a detailed study of the uncertainty in an existing one: the standard chiral flexoelectro-optic effect method. 5,9,[43][44][45][46][47][48][49][50][51][52][53] The combination (e 1 − e 3 ) is determined, which is known as the bulk flexoelectric coefficient; it governs the flexoelectric response of a system for which the electric field is constant. 20 The purposes of this paper are: (1) To establish firmly the chiral flexoelectro-optic effect as an accurate method for the measurement of (e 1 − e 3 ), where random uncertainties and systematic effects have been analyzed and reduced.…”

Giant Flexoelectro-optic Effect with Liquid Crystal Dimer CB7CB

“…A convenient value characterizing flexoelectric properties of a LC material is flexo-elastic coefficient e f / K 8910111213141516171819. Flexoelectric rotation of the HA always competes with undesired unwinding of the ULH CLC texture into a non-helical state due to dielectric coupling to applied electric field.…”

“…Most commonly the ULH is generated in cells with a uniform planar alignment layer as a result of a controlled rate cooling of CLC mixture from isotropic phase down to chiral nematic phase with small electric field applied across the cell gap167202122. Another method to generate a well-aligned ULH CLC texture is mechanical deformation or shearing of cell substrates with respect to each other with58101123 or without224 applied electric field. A few of experimental works have reported generation of a well-aligned ULH texture using a combination of controlled rate cooling of a CLC and shearing of cells substrates with applied electric field12131617.…”

A new series of siloxane liquid crystalline dimers exhibiting the antiferroelectric phase

“…Most of these studies have dealt with monomeric (monomesogenic) systems, however, during the last two decades polymeric systems have also been extensively investigated. In addition to those major groups it is also possible to create many well defined oligomeric systems with very attractive properties resulting from the combination of polymeric and monomeric properties in the oligomeric materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The simplest of these are the dimeric systems.…”