TGB A phase in a series of swallowtailed chiral liquid crystals

Abstract

A homologous series of chiral materials, 1-butylpentyl (S)-2-{6-[4-(4'-alkoxyphenyl)- benzoyloxy]-2-naphthyl}propionates, BPmPBNP (m=6-16), derived from a chiral moiety, (S)-2-(6-hydroxy-2-naphthyl)propionic acid, in conjunction with a swallowtail group attached to the external side of the chiral centre, has been synthesized and their mesomorphic phases have been studied. There were two frustrated phases: a blue (BP) phase and a twist-grain- boundary (TGBA) phase found enantiotropically in all materials. It is worth noting that, depending on the nature of the terminal chain length, two types of filament textures were observed in the TGB A phase: a vermis (filament) texture and a spiral filament texture. The formation of the TGB A phase was rationalized as due to the steric effect caused by the swallowtail of the materials. All materials exhibited a wide temperature range of the SmA phase, but only three materials (m=12, 13 and 16) possessed a monotropic SmC* phase over a narrow temperature range, indicating that the swallowtailed materials inhibit the formation of a tilted smectic phase.