Liquid crystalline imidazolium salts bearing 5-phenylpyrimidine: dependence of mesomorphic properties on spacer lengths, terminal N-alkyl group and counterions

Abstract

New imidazolium salts bearing substituted 5-phenylpyrimidine mesogenic groups were synthesised and their mesomorphic properties were studied by differential scanning calorimetry, optical microscopy and powder X-ray diffraction methods (WAXS, SAXS). The parent 5-phenylpyrimidines with the terminal bromide group at the alkoxy spacer exhibited low clearing points and smectic mesophases in narrow temperature ranges. The incorporation of the N-alkylimidazolium cationic core, connected with 5-phenylpyrimidine via an alkoxy spacer, remarkably improved the stability of the mesophases. The imidazolium salts with 5-phenylpyrimidine group formed smectic A phases, stable over broad temperature intervals. The influences of the counteranion, the length of terminal alkyl group and alkoxy spacer on the mesomorphic behaviour of the 5-phenylpyrimidine substituted N-alkylimidazolium salts were investigated in detail.

Keywords:

• calamitic
• ionic liquid crystals
• imidazolium salts
• phenylpyrimidines

Acknowledgement

Generous financial support by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, the Ministerium für Wissenschaft, Forschung und Kunst des Landes Baden-Württemberg, the Bundesministerium für Bildung und Forschung (BMBF shared instrumentation grant 01RI05177), the Gesellschaft Deutscher Chemiker (grant for G.F.S.) and the International Max-Planck-Research School for Advanced Materials (fellowship for M.K.) is gratefully acknowledged.