Liquid crystalline guanidinium phenylalkoxybenzoates: towards room temperature liquid crystals via bending of the mesogenic core and the use of triflate counter ions

Abstract

A series of guanidinium salts 1(C _n ) _m –4(C _n ) _m  X bearing phenyl alkoxybenzoate cores have been synthesised and their mesomorphic properties have been investigated by polarising optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction experiments (small-angle X-ray scattering and wide-angle X-ray scattering). While compounds 1(C₁₂)₁ X and 3(C₁₂)₁ X with one alkoxy chain showed smectic A (SmA) phases irrespective of the counter ion, compounds 1(C₁₂)₂ OTf and 3(C₁₂)₂ OTf with two alkoxy chains displayed SmA phases and the corresponding chlorides 1(C₁₂)₂ Cl and 3(C₁₂)₂ Cl displayed Col_h. Guanidinium salts 1(C _n )₃–4(C _n )₃ X with three alkoxy chains showed Col_h phases. Whereas the use of cyclic guanidinium head groups rather than acyclic ones had only a minor influence on the mesophase properties, melting points were significantly decreased by bent core units instead of linear core units. Replacement of chloride counterions by triflate lead to a further depression of the clearing points and shifted the mesophase towards room temperature.

Keywords:

• guanidinium
• ionic liquid crystals
• triflates
• room temperature
• thermal stabilisation

Acknowledgements

Financial support from the Bundesministerium für Bildung und Forschung (BMBF-Verbundprojekt Nr. 01 RI 05177), the Studienstiftung des Deutschen Volkes (fellowship for M. Butschies), the Deutsche Forschungsgemeinschaft, the Ministerium für Wissenschaft, Forschung und Kunst des Landes Baden-Württemberg, and the Fonds der Chemischen Industrie is gratefully acknowledged. We would particularly like to thank Mr C. Schneck for the important TGA investigations.