Photosensitive bent-core nematic liquid crystals with various linking units in the side arms: Structure-properties relationships

We present two isomeric series of photosensitive bent-core liquid crystals possessing a lateral chlorine atom in the central resorcinol unit and various linking units in the side arms. With the aim to tune properties of the nematic phase, we have varied the type of the linking unit in the lengthening arm with rising rigidity from benzoate ester, biphenyl, cinnamate, Schiff base to stilbene moieties. In addition to that, we have changed the position of the lateral substituent (chlorine) as well. The mesomorphic properties of the materials have been determined from differential scanning calorimetry, polarizing optical microscopy, dielectric spectroscopy and X-ray studies. We show that synergy of the linking unit with the effect of the lateral substituent gives rise to broad temperature range of mesophases — the nematic phase as well as a SmCP phase. Thanks to the presence of the photosensitive group in the molecular structure, we have been able to transform both mesophases to the isotropic phase under UV light. The chemical structure–mesomorphic properties relationships are discussed with the aid of ab initio calculations and the results presented in context with experimental data.