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 Colh. Guanidinium salts 1(C n )3–4(C n )3 X with three alkoxy chains showed Colh 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.