A different kind of Lyotropic Liquid Crystalline Phase: The case of Orange-II and gamma-Cyclodextrin

Liquid crystallinity, either thermotropic or lyotropic, arises from species which are either rod or disk shaped. Lyotropic systems occur when an asymmetrically shaped species is dissolved in a solvent at a concentration high enough to force the formation of an anisotropic phase. For either case, the asymmetrically shaped species can be built solely from covalent bonds, where no additional assembling process is required for the species to have an appropriate aspect ratio. Here, we report on the formation of a different kind of lyotropic liquid crystal formed by the non-covalent association of two species, g-cyclodextrin and a dye molecule, Orange II, in water as the solvent. This system is different in that it requires two different compounds that self-assemble to build a larger species with geometrical asymmetry. In an effort to understand the complexation and the formation of the liquid crystalline phase, we present data on UV-Visible spectra, conductometric titrations, fluorescence spectroscopy as well as heat capacity measurements on the formation of the anisotropic structure in water solutions. The studies point to a stoichiometry of 2 dye molecules per g-cyclodextrin, that eventually form a rodlike entity, giving rise to the formation of a liquid crystalline phase.