Quasi-liquid crystals

Abstract

Photo- and thermochromic conversion of spiropyrans into merocyanines¹ is used to ‘engineer’ new types of molecular organizates^2–6, based on the capability of the merocyanine dyes to give giant molecular stacks⁷. One type of spiropyran–merocyanine organizate, the so-called quasi-crystal, is formed when the photochromic reaction occurs in an electrostatic field. The quasi-crystals are composed of assemblies of dipolar molecular stacks covered by amorphous materials and aligned along the field^2,3. Quasi-crystals exhibit optical nonlinearity⁴. Other types of organizates occur in macromolecules bearing spiropyran side groups^5,6. Both inter- and intramolecular stacking of merocyanine side groups have been disclosed. Here we describe a new spiropyran–merocyanine organizate obtained in spiropyrans containing mesogenic groups. These materials exhibit some features of liquid crystals (birefringence, orientation in an electric field), but have structures that are completely different from conventional liquid crystals. We propose that organic compounds with this novel form of organization be called quasi-liquid crystals (QLCs).