Chromonic liquid crystalline phases

Abstract

Chromonic systems are lyotropic mesophases formed by soluble aromatic compounds. The basic structural units in these systems are stacks of molecules (rather than individual molecules or micellar assemblies). There are two common chromonic phases: a more dilute phase consisting of a nematic array of columns (the N phase) and a more concentrated phase in which the columns lie in a hexagonal array (the M phase). Chromonic phases are formed by a range of compounds, including drugs, dyes and nucleic acids, typically with three or four fused aromatic rings. They have distinctive optical textures and characteristic multi-peritectic phase diagrams (in contrast to the multi-eutectic phase diagrams of conventional amphiphiles). Many commercial dyes have proved to be chromonic, but the ability to form liquid crystalline phases has been incidental to their use. However, recent studies have shown that the combination of self-ordering, ease of alignment, sensitivity to changing conditions and additives, coupled with their optical and electro-optical properties, gives these systems unique and potentially valuable properties. It is expected that these will lead to a new generation of applications. It is predicted that there will be increased emphasis on the development of a range of sophisticated devices, either produced from, or actually incorporating chromonic phases. These include polarisers, optical compensators, light-harvesting devices, and biosensors for medical diagnosis.