Azo functionalised achiral bent-core liquid crystals: observation of photo-induced effects in B7 and B2 mesophases

Abstract

Three structural variants of azo substituted achiral bent-core compounds are reported. Here, the effect of symmetrical and non-symmetrical arms at 1,3-positions of the central phenyl ring on the mesogenic properties of the resulting bent-core azo compounds is studied. The structures of all the compounds synthesised are confirmed by the organic spectroscopic methods. The liquid crystalline properties are investigated using polarising optical microscopy, differential scanning calorimetry and X-ray diffraction studies. It was found that the non-symmetrical molecules are more conducive to mesomorphism than the symmetrical ones. We observed B1 (Colr), B2 (SmCAPA) and B7 mesophases in these compounds. The B7 mesophase was found to have a modulated layer structure. Interestingly, a reversible field-induced transition from the B7-like structure to the racemic SmCAPF was also observed. We also report the photo-induced studies in the B7 mesophase and make a comparison of these results with those obtained in a B2 mesophase. From our studies, we observed that these effects are more profound in the case of B7 mesophase when compared to the B2 mesophase in such systems.