Helical superstructure from an achiral banana-shaped liquid crystal

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Abstract
In the banana-shaped achiral molecular system reported here, 1,3-phenylene bis[4-(3-chloro-4-n-octyloxy-phenyliminomethyl) benzoate] (PBCOB) and 1,3-phenylene bis[4-(3-fluoro-4-n-octyloxy-phenyliminomethyl) benzoate] (PBFOB), their smectic mesophases, including a switchable banana phase B7, were identified by differential scanning calorimetry (DSC), X-ray scattering and polarizing optical microscopy (POM) studies. Both the left- and right-handed helical domains are spontaneously formed upon cooling from isotropic liquid to the switchable banana phase (By). The homeotropic alignment and ferroelectric properties of banana-shaped liquid crystal are investigated. The spontaneous polarization for PBCOB is about 50 nC/cm2. Doping the PBCOB with a cyanohydrin-contain chiral smectic liquid crystal resulted in more right-handed helical structures.