Liquid crystalline nano-segregated structures in hydrogen-bonded complexes of fluoroalkyl substituted benzoic acids

Several new benzoic acid derivatives having perfluorinated substituents were synthesized and their hydrogen-bonded complexes with 4,4'-dipyridyl were prepared. In these acid/base complexes the incompatibility between perfluoroalkyl moieties and hydrocarbon parts is large, which can lead to organize nano-segregation structures. We have found in one of such complexes, that has a long flexible fluorinated moiety, a thermotropic cubic phase with Ia3d symmetry formed by double gyroid of two interpenetrating jointed rod networks with an estimated cell parameter of 10.9 nm. Furthermore another complex with a branched long perfluoroalkyl terminal chain exhibits a first order smectic A to smectic C phase transition, which is confirmed with thermal analysis detecting a large enthalpy change of 5.3 kJ(.)mol(-1), X-ray scattering experiments revealing a tilt angle jump, and polarized optical microscopy observing a remarkable texture change at the phase transition temperature.