Chiral liquid crystal matrix

Figure 3.1. Induced CD (curves 1-5) and UV (curve 6) spectra of substrate N-acetylaminocinnamic acid included into chiral liquid crystal matrix of cholesteryl tridecanoate in 1-butanol at 54 C.

Pavlov V.A., Spitsyna N.l. and Klabunovskii E.I. (1983) Enantioselective hydrogenation in the presence of cholesteryltridecanoate as chiral liquid crystal matrix, Izv. Acad. Sci. SSSR. Ser. Khim. (russ.) 1653-1656 Chem. Abstr. 1983, 99,194048). 

Another approach is to build up a polymer network aroimd a complex. Pavlov et al. studied a chiral liquid crystal matrix, in which the Wilkinson catalyst, [RhCl(PPh3)3] was embedded in cholesteryltridecanoate and catalyzed the enantioseleetive hydrogenation of 2-acetamidocinnamic acid into A-acetylphenylalanine with an ee of 60% (see details in Chapter 3). 

It can be safely predicted that applications of liquid crystals will expand in the future to more and more sophisticated areas of electronics. Potential applications of ferroelectric liquid crystals (e.g. fast shutters, complex multiplexed displays) are particularly exciting. The only LC that can show ferroelectric property is the chiral smectic C. Viable ferroelectric displays have however not yet materialized. Antifer-roelectric phases may also have good potential in display applications. Supertwisted nematic displays of twist artgles of around 240° and materials with low viscosity which respond relatively fast, have found considerable application. Another development is the polymer dispersed liquid crystal display in which small nematic droplets ( 2 gm in diameter) are formed in a polymer matrix. Liquid crystalline elastomers with novel physical properties would have many applications. 

Figure 3.2. Induced CD (curves 1-3) and UV (curve 4) spectra of Wilkinson catalyst, RhCl(PPli3)3, included into the chiral matrix of the liquid crystal cholesteryl stearate at 67"C in 1-butanol (adapted from Pavlov etal.

The symmetry approach to ferroelectricity in liquid crystals can be realized not only for individual substances but also for multicomponent systems. For low-molar-mass ferroelectric liquid crystals, most applications use LC mixtures with two main components a nonchiral matrix providing the tilted smectic structure and a chiral dopant [7]. As for the preparation of FLCPs, mixing of a smectic C polymer with a chiral dopant also results in a ferroelectric chiral smectic system [74]. Japanese authors [75,76] have carried out systematic studies on mixing tilted smectic polymers with low-molar-mass ferroelectric liquid crystals. 

Liquid crystal induced circular dichroism (LCICD) examines the differential absorption of circularly polarized radiation by an achiral solute oriented in a cholesteric liquid crystal. The circular dichroism results from an induced Cotton effect in the achiral solute due to the macroscopic chirality of its ordering in the helical solvent matrix. The effect has been shown theoretically to arise... 

The principles described in this paper are of importance for polymerizations not only in the solid state, but also in ordered systems in general. Thus, to a greater or lesser extent they must be relevant to reactions in liquid crystals, membranes, surface films, and so on, and thus for both natural and synthetic systems. The polymers produced by such processes may be expected to have unusual, and even possibly unique, chemical, physical, and mechanical properties, particularly as long as maintained in the parent matrix. Philosophically, these reactions in chiral aggregates are of interest as one possible mode of abiotic formation of chiral polymers. 

The helix induction force for the series of copolymers examined coincides with the corresponding value for a mixture of low-molecular-weight liquid crystals—p-butoxybenzylidene-p -butylaniline with cholesteryl pnq)ionate—where there are no specific interactions in the nematic matrix, and the chirality is caused by the cholesterol fragment... 

Ferroelectric side-chain liquid crystal polymers (fLCPs) have been synthesized only recently. (see Chapter 8). Because of the dilution of chiral side chains in the backbone matrix, the spontaneous polarization is weaker than in the monomer chiral smectics, although Kapitza and others recently reported polysiloxane-based fLCPs with spontaneous polarization comparable to that observed for monomer liquid crystals. 

In particular, for the synthesis of optically pure chemicals, several immobilization techniques have been shown to give stable and active chiral heterogeneous catalysts. A step further has been carried out by Choi et al. [342] who immobilized chiral Co(III) complexes on ZSM-5/Anodisc membranes for the hydrolytic kinetic resolution of terminal epoxides. The salen catalyst, loaded into the macroporous matrix of Anodise by impregnation under vacuum, must exit near the interface of ZSM-5 film to contact with both biphasic reactants such as epoxides and water. Furthermore, the loading of chiral catalyst remains constant during reaction because it cannot diffuse into the pore channel of ZSM-5 crystals and is insoluble in water. The catalytic zeolite composite membrane obtained acts as liquid-liquid contactor, which combines the chemical reaction with the continuous extraction of products simultaneously (see Figure 11.28) the... 

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