Ionic liquid crystals derived from guanidinium salts: induction of columnar mesophases by bending of the cationic core

Abstract

Meta-alkyloxyguanidinium salt-based ionic liquid crystals 3–5, 7 and 9 were synthesised and investigated with respect to the influence of meta-substitution of the cation on the mesomorphic properties. As expected, bending of the mesogenic cation in ion pairs with simple counterions (3–5) decreased melting points irrespective of the anion, but clearing points were influenced by the anion radii. SmA mesophases were formed in all cases. The mesophase formation in guanidinium sulphonates 7 and 9, however, depended not only on meta-substitution but also on the anion, the respective difference between alkyl chain lengths in cation and anion and the number of alkyloxy substituents on the sulphonate, for which a change of mesophase type from smectic to columnar phases was observed. For two derivatives, 7e and 9b, room temperature SmA and Col_h mesophases could be obtained that were stable for a temperature range of 91 K and 55 K, respectively. A packing model for both smectic and columnar phases based on powder XRD data was proposed.

Keywords:

• guanidinium
• ionic liquid crystals
• columnar
• smectic
• ion pairs

Funding

Generous financial support by the Bundesministerium für Bildung und Forschung (BMBF shared instrumentation [grant number 01 RI 05177]), the Ministerium für Wissenschaft, Forschung und Kunst des Landes Baden-Württemberg, the European Commission (ERASMUS fellowship for L. A.) and the Fonds der Chemischen Industrie (Kekulé fellowship for S. B.) is gratefully acknowledged.

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