Columnar liquid crystals derived from crown ethers with two lateral ester-substituted ortho-terphenyl units: unexpected destabilisation of the mesophase by potassium iodide

Abstract

Gallic acid substituted ortho-terphenyl dimers linked by a central [18]crown-6 ether and their KI complexes were synthesised and characterised by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. With one exception, all salt free derivatives were liquid crystalline. They formed hexagonal columnar mesophases, whose columnar order is retained even upon cooling to room temperature. An odd–even effect of the clearing temperatures was observed with higher clearing points for compounds bearing even-numbered side chains as compared to odd-numbered ones. The calculation of molecules per unit cell resulted in Z ∼ 2, thus a disc with a dimeric subunit of two molecules oriented perpendicular to each other is assumed. In contrast, all KI complexes were non-mesomorphic.

Keywords:

• crown ether
• cation complexation
• columnar liquid crystals
• o-terphenyl
• gallic acid

Acknowledgements

Generous financial support by the Deutsche Forschungs-gemeinschaft, the Max-Planck-Gesellschaft (International Max Planck Research School for Advanced Materials fellowship for M. K.), the Fonds der Chemischen Industrie, the Bundesministerium für Bildung und Forschung (BMBF grant #01 RI 05177) and the Ministerium für Wissenschaft, Forschung und Kunst des Landes Baden-Württemberg is gratefully acknowledged. We would like to thank one of the referees for valuable suggestions.