Liquid Crystalline Order from <i>ortho</i>-Phenylene Ethynylene Macrocycles

Abstract

Triangular <i>ortho</i>-phenylene ethynylene (<i>o</i>-PE) cyclic trimers represent a novel member of shape-persistent macrocycles. Shape-persistent cyclic structures remain of great interest as molecular components in the fields of supramolecular materials, host−guest chemistry, and materials science. Novel discotic liquid crystalline properties are reported from triangular-shaped <i>o</i>-PE macrocycles containing branched alkoxy- and/or triethylene glycol (TEG) side chains using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The macrocycles self-assemble into thermotropic rectangular columnar (Col_r) (for <b>M1</b>), hexagonal columnar (Col_h) (for <b>M2</b>), and discotic nematic (for <b>M3</b>) mesophases at room temperature. This work shows clearly that electron-rich PE macrocycles can form LC materials. Alkyl side chains in <b>M1</b> promote order, while hydrophilic side chains of <b>M2</b> generate an amphiphilic structure that provides a different driving force for organization. The ability to create ordered self-assembling materials from these novel electron-rich macrocycles is important in nanotechnology.