Optical activity ferroelectrics

Fig. 2. Domain structure in Pb5Ge30n, an optically active ferroelectric. 180° domains in a c-cut crystal are clearly visible in plane-polarized white light with analyzer positioned at 87.5° to the polarizer. The crystal thickness is 0.5 mm and the small hexagonal domains are about 0.1 mm in diameter.

Extensive research has already been carried out on incorporation of fluorine into molecules which can lead to profound and unexpected results on biological activities and/or physical properties [ 1 - 5]. In particular, optically active fluorine-containing molecules have been recognized as a relatively important class of materials because of their interesting characteristics and potential applicability to optical devices such as ferroelectric or antiferroelectric liquid crystals [6-11]. Recent investigations in this field have opened up the possibility for the... 

Chien and Cada [42] have prepared optically active and photoactive SCLC copolymers, 15, with the 4-alkoxyphenyl-4 -alkoxycinnamate chromophore, with the intention of creating LC polysiloxane networks that could be used to prepare macroscopically oriented organic ferroelectric polymers for electro-optical devices. Optical activity was introduced into the polymer by the use of a chiral spacer. Those copolymers which were mesogenic exhibited properties characteristic of a Sc. phase. UV-irradiation of thin films of the polymers in their mesomorphic states at 90°C, led to a loss of the IR absorption at 1635 cm-1 that is due to the cinnamate double bond, and to cross-linking. Long-term irradiation led to... 

The inverse-micelle approach may also offer a generalized scheme for the preparation of monodisperse metal-oxide nanoparticles. The reported materials are ferroelectric oxides and, thus, stray from our emphasis on optically active semiconductor NQDs. Nevertheless, the method demonstrates an intriguing and useful approach the combination of sol-gel techniques with inverse-micelle nanoparticle synthesis (with OTO erafe-temperature nucleation and growth). Monodisperse barium titanate, BaTiOs, nanocrystals, with diameters controlled in the range from 6-12nm, were prepared. In addition, proof-of-principle preparations were successfully conducted for Ti02 and PbTiOs. Single-source alkoxide precmsors are used to ensure proper stoichiometry in the preparation of complex oxides (e.g. bimetallic oxides) and are commercially available for a variety of systems. The... 

Recent employment of optically active fluorinated compounds for biologically active substances (7-2) or ferroelectric liquid crystals (3-5) has emphasized the versatility of these chiral molecules, while few methods have been reported for the preparation of such materials in a highly diastereo- as well as enantioselective manner. On the other hand, recent investigations in this field have opened the possibility for the introduction of chirality via asymmetric reduction or optical resolution by employing biocatalysts such as baker s yeast (6-75) or hydrolytic enzymes (16-20), respectively (27-23), along with the conventional chemical methodology (24-27). Chiral materials thus obtained may also be utilized in diastereoselective reactions which create new chiral centers (77). In this paper, the authors would like to discuss our recent progress in the preparation of optically active fluorinated compoounds and the effect of fluorine atom(s) on the reactivity and selectivity. 

It first proved that a cisoid conformation (U-shape) does not prevent mesophase formation, but also that this type of structure can lead to potentially ferroelectric materials, since compound 58 was obtained as a mixture of isomers, some of them being optically active (planar chirality). 

Watanabe, S. Sakai, Y. Takeda, M. Kitazume, T. Yamazaki, T. Synthesis of optically active y-lactones and dopants for ferroelectric liquid crystals possessing a trifluoromethyl group. J. Fluorine Chem. 1994, 67, 149-152. 

SmC C2 X T(2) Optically active chiral analogy of SmC phase showing macroscopic periodicity with twist axis perpendicular to smectic layers. Quasi-long-range positional order along the layer normal and two-dimensional liquid-like structure within the layer plane. Single layers of the same symmetry may form diffcaent phases in the bulk ferroelectric (SmC ), antiferroelectric (SmCA ) and ferrielectric (SmCy ). 

Beresnev, L.A., Blinov, L.M., Baikalov, V.A., Pozhidayev, E.P., Purvanetskas, G.V., Pavluchenko, A.I. Ferroelectricity in tilted smectics doped with optically active additives. Mol. Cryst. Liq. Cryst 89, 327-338 (1982)... 

Most liquid crystal phases are centrosymmetric and nonferroelectric. Symmetry low enough for ferroelectric-ity to occur is found only in smectic phases that are both tilted (as explained below) and optically active (chiral). 

These piezoelectric materials without i are included in point groups (except O = 432) of 2" to 7 columns as shown in Table 1. Here, the 1 column is Laue group with i, and to 6 for optical activity, 5 to 7 for pyroelectricity, and 4 and 5 for enantiomorphism. Ferroelectric materials are ones with spontaneous polarization in pyroelectricity 5 to 7 h All ferroelectric materials show piezoelectricity, but the reverse is not true, that is, not all piezoelectric materials show ferroelectricity. 

On a macroscopic scale, the spontaneous polarization vector in the optically active phase spirals about an axis perpendicular to the smectic layers (Fig. 20), and sums to zero. This macroscopic cancellation of the polarization vectors can be avoided if the helical structure is unwound by surface forces, by an applied field, or by pitch compensation with an oppositely handed dopant. The surface stabilized ferroelectric liquid crystal display utilizes this structure and uses coupling between the electric field and the spontaneous polarization of the smectic C phase. The device uses a smectic C liquid crystal material in the so-called bookshelf structure shown in Fig. 21a. This device structure was fabricated by shearing thin (about 2 i,m) layers of liquid crystal in the... 

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