Supramolecular chiral liquid crystals. The liquid crystalline behaviour of mixtures of 4,4′-bipyridyl and 4-[(S)-(-)-2-methylbutoxy]benzoic acid

Abstract

The thermal behaviour of binary mixtures of 4,4′-bipyridyl and 4-[(S)-(-)-2-methylbutoxy]benzoic acid has been investigated. The two components are not liquid crystalline. By comparison, mixtures containing between 0.1 and 0.5 mole fraction of 4,4′-bipyridyl exhibit mesogenic behaviour; specifically, chiral nematic, blue and smectic A phases are observed. The induced mesogenic behaviour is attributed to the formation of elongated hydrogen bonded complexes and this view is supported by infrared spectroscopy. The crystal structure of the complex containing 0.3 mole fraction of 4,4′-bipyridyl was determined using X-ray diffraction. This confirmed the formation of linear hydrogen bonded complexes in which two acid fragments are attached to a central 4,4′-bipyridyl core and supports the view that such complexes are responsible for the liquid crystalline behaviour of these mixtures.