Smectic Mesophase Behavior of Dimeric Compounds Showing Antiferroelectricity, Frustration and Chirality

We have prepared a series of dimeric compounds, m OAM5AMO m , which comprise two Schiff's base mesogens. These compounds formed three types of fluid smectic liquid crystals. When the alkoxy tail length is short ( m =4 and 6), the alkoxy tail groups mix randomly with the alkyl spacer groups, resulting in the SmCA s phase. The compounds with m longer than 14 form the SmCA b phase with a bilayer character, in which the spacer and tail groups segregate from each other and consequently two mesogenic layers (so-called bilayer) are included within a repeat unit. In such a bilayer association of twin dimers, spontaneous polarization appears in each bilayer. In this SmCA b phase, furthermore, the molecules are tilted to the layer so that chirality is spontaneously formed in addition to ferroelectricity. The structure was identified as SmC A P A type. The compounds with intermediate m of 8–12 formed the frustrated SmCA f phase with a density modulation (frustration) along the layer. On cooling from the smectic phases, crystallization takes place for m OAM5AMO m with m =4–8, while the chiral Cr blue phase with the TGB-like helical structure was clearly identified with m =14–18. The structure and properties of these exotic phases in twin dimers are described in detail.