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...

The synthesis, purification, characterization, and liquid-crystalline properties of side-chain polysiloxanes bearing mesomorphic 1,1′-or 1,3-disubstituted ferrocene units are reported. The polymers were prepared by grafting the appropriate vinyl-containing ferrocene monomer onto commercially available poly(hydrosiloxane)s following a standard procedure. The monomers gave smectic A or smectic A and smectic C phases depending on the length of the flexible chains connected to the ferrocene unit. X-ray diffraction indicated that the polysiloxanes exhibited disordered smectic phases. Variation of the d-layer spacing determined for the polymers containing either 100% or 15-18% of the 1,1′-disubstituted ferrocene monomer (with the longest terminal alkyl chain) revealed the presence of smectic A and smectic C phases. Thermogravimetry showed a good thermal stability for the polymers.

We describe the synthesis, characterization and properties of the first optically-active 1,3-unsymmetrically disubstituted ferrocene derivative which is to exhibit smectic C* and smectic A* phases.Symmetry breaking operations and chirality have held centre stage in the fundamental investigations and applications of liquid crystals. 1,2 Furthermore, recent studies on mesogens with banana-shaped molecular structures have shown that chiral induction in self-organizing systems is possible even though the materials are themselves achiral. 3,4 The search for new chiral effects in mesomorphic systems prompted us to synthesize unsymmetrically 1,3-disubstituted ferrocene-containing liquid crystals, 5 where the different substituents at the 1-and 3-positions generate structures with planar chirality (Fig. 1). A representative example is illustrated by compound 1 (see Scheme 1); the two substituents are differentiated by the length of the alkyl chains and the orientation of the outer ester groups. Homologues of this material were prepared in racemic form from (±)-2 5 (see Scheme 1). Over the entire range of the compounds studied, smectic C (SmC) and smectic A (SmA) phases were observed, and in some cases an additional nematic phase was detected.The presence of the SmC phase in this family of compounds provided a unique challenge to make the materials optically active (SmC*) and thereby ferroelectric. Of course symmetrically 1,3-disubstituted ferrocene derivatives have the potential to exhibit ferro-or antiferro-electricity if the packing constraints of the molecules within the layers induce a restricted rotation of the molecules about their long axes. Within this packing constraint, the V-shaped molecules will pack together to give a non-symmetric arrangement thereby leading to the induction of non-linear properties.Ferroelectric liquid crystals are of considerable interest in switchable, half-wave plate, bistable light-valves. For ferrocenyl liquid crystals, SmC* phases have been reported only for two mono-substituted derivatives. 7,8 Chirality was introduced into the peripheral side-chain by means of asymmetric carbon atoms, but for the two materials no ferroelectric behavior was described.In addition to the investigation of the dependency of ferroelectricity on planar chirality, this study allowed us to probe the influence of the chiral unit, which is embedded in the central region of the molecular structure, on the self-organization process and mesophase formation. In metallomesogens, planar chirality was elegantly exploited by Malthête and coworkers who reported optically-active butadienetricarbonyliron liquid crystal complexes. 9 The spontaneous polarization of one of the complexes was determined, and a value of 32 nC cm 22 was obtained (response time: 9 ms). 9b We report, herein, the synthesis, mesomorphic behavior and ferroelectric properties of the liquid-crystalline Fc derivative (+)-1 (Scheme 1). The latter structure was selected because the corresponding racemic analogue gave the broadest SmC range among the...

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