Host antiferroelectrics

Photochemical polarization flip was immediately extended to antiferroelectric LCs (AFLCs), and it was found that in azobenzene guest/AFLC host systems, polarization flip could be induced photochemically and effectively, as shown in Figure 3.1331 Novel photochromic molecules to induce polarization flip effectively have been explored, and molecular design on the basis of large Ps resulting from chiral cyclic carbonates has been found to be quite effective. An azobenzene dopant containing a... 

The synthesis of nonchiral smectic liquid crystals is a broad topic for discussion, however, it can be divided into subsections in two different ways. For example, smectic systems can be split into metallomesogens and nonmetallomesogens, alternatively, they can be divided into materials for (1) meso-phase structure elucidation and classification [ 1 ], (2) property-structure correlations [2] and (3) host systems for ferroelectric and antiferroelectric mixtures. In the following sections template structures used for the synthesis of smectic materials will be described, followed by discussions of the syntheses of materials that have extensive histories in the elucidation of smectic phase structures, and finally of the syntheses of smectogens that are useful in applications. 

Requirements for materials with strong positive dielectric anisotropies for storage applications are usually met by the availability of the 4-alkyl and 4-alkoxy-4 -cyano-biphenyls. The syntheses of these materials have been discussed in the above sections and so will not be discussed further in this section. The demands of ferroelectric and antiferroelectric applications, however, require that the syntheses of host systems are discussed in more detail. 

The synthesis of the first achiral host material that exhibits a smectic Cau phase [36] (achiral version of the antiferroelectric phase) is shown in Fig. 42. It can be seen that this material has three aromatic rings and two ester groups, but in addition it has a swallow-tail unit. This unit (for no apparent reason at the moment) stabilizes the formation of smectic Cai, phases. The material like a ferroelectric host can be doped with a chiral dopant to give an antiferroelectric mixture. 

Note added in proof Quite recently, Itoh et al. reported that the phase in these pyrimidine host mixtures is not antiferroelectric but ferroelectric and that the typical tristable switching results from an ultra-short pitch of about 50 nm. (K. Itoh, Y. Takanishi, J. Yokoyama, K. Ishikawa, H. Takezoe and A. Fu-kuda, Jpn. J. Appl. Phys. 1997, 36, L784). 

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