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.

Two ferrocene-containing low molar mass organosiloxane liquid-crystalline materials have been synthesised and their phase-transition behaviour investigated. The v-unsaturated ferrocene precursor was hydrosilylated by addition of pentamethyldisiloxane or heptamethyltrisiloxane in the presence of platinum divinyltetramethyldisiloxane complex. The ferrocene precursor presents smectic A and smectic C phases; the disiloxane compound exhibits a smectic C phase; the trisiloxane compound shows a smectic C phase and two higher order smectic phases. Tilt angle measurements were performed on samples oriented on polytetrafluoroethylene (PTFE) friction deposited layers since rubbed polyimide (PI ) only gave very poor alignment. For the precursor the tilt angle was found to be very small, close to 2°, while for the two organosiloxane ferrocene compounds it was close to 28°and almost independent of temperature. These compounds exhibited ferroelectric electro-optic switching properties when doped with 1-2% w/w of chiral mesogens.(structures 2 and 3), which represent a novel family of metalIntroduction based anisotropic materials (see Synthesis and Fig. 1). We will There is a growing interest in metal-containing liquidpresent data for two homologues, containing 2 and 3 silicon crystalline materials1,2 that combine some of the properties of atoms, in comparison with the v-unsaturated ferrocene precurmetals with those of mesogenic moieties since this could lead sor. This will allow us to demonstrate that, despite its relatively to processable materials with interesting anisotropic optical, small size compared to the bulky ferrocene mesogenic group, electronic and magnetic properties. Owing to its unique redox the siloxane moiety plays an important role in the phase characteristics, ferrocene is a valuable unit for building up stability, phase sequence, electro-optic properties and quality switchable systems3 and recently, electron transfer was used of the surface alignment. to generate mesomorphism in the ferrocene-ferrocenium redox system.4Ferrocene-containing side-chain liquid-crystal polymers Experimental(SCLCPs) have been reported in the literature.1,2,5 The SCLCPs offer several advantages over the low molar mass Synthesis liquid crystals in that they have better mechanical characterThe ferrocene precursor 1 was synthesised as previously istics, a broader mesomorphic range and a reduced or supdescribed.2 1,1,1,3,3-Pentamethyldisiloxane, 1,1,1,3,3,5,5-heppressed tendency to form crystalline phases. However, because tamethyltrisiloxane and the platinum catalyst (platinumof the rigidity of the polymer backbone, the SCLCPs are divinyltetramethyldisiloxane complex, 3-3.5% platinum conusually highly viscous and therefore have long switching centration in vinyl terminated polydimethylsiloxane, neutral ) response times.6 The SCLCPs based on flexible polysiloxane were purchased from Fluorochem. Toluene was freed of thiobackbones have shorter response times than those based on phene according to standard procedures and then dried over m...

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The physical characteristics of a new fluorinated organosiloxane material are presented, and compared to those of its non-fluorinated homologue. The fluorinated material has a high Ps (200 -450 nC/cm2) and a high tilt angle (-38") over a 100°C wide temperature range. Both materials exhibit antiferroelectric phases. As the fluorinated material is cooled, its behaviour becomes more ferroelectric-like. We discuss this behaviour in relation to the molecular structure of the materials.

We present a series of chiral nematic liquid crystal bimesogenic compounds based on estradiol as the chiral unit and the highly polarizable cyanobiphenyl as the terminal group. The mesophases have temperature ranges up to 40 "C wide, entering the isotropic phase at about 100 "C. We have observed the flexoelectro-optic effect and have found that the average flexoelectric coefficients of our materials are high (2 +5x1O-l2 Cm-'). The electro-optic response times, for 0 to 90% of transmitted intensity, are of the order 1 ms.