Azo-functionalised liquid crystalline dimers composed of bent-core and rod-like moieties: synthesis and mesomorphic properties

Abstract

Three new series of azo-functionalised dimers composed of banana (bent-core) and rod-like moieties connected via flexible alkylene spacer have been synthesised and characterised. Here, the molecular structure – liquid crystalline property relationship has been studied, mainly by varying the spacer chain length in addition to the effect of polar –CN end group. All the compounds synthesised are characterised by the organic spectroscopic methods. The thermal behaviour of these dimers is investigated by the polarising optical microscopy, differential scanning calorimetry, electro-optical and X-ray diffraction studies. Interestingly, we observed a variety of mesophases in these dimers, namely, N, SmA, SmC, SmX, SmY, Col_x and Col_y. We even observed a re-entrant phenomena of the mesophases in one of these dimers. The nematic phases of some of these dimers exhibit electric field induced textural patterns. The dimers are photosensitive and the T _NI was found to decrease as the illuminated light intensity increases.

Keywords:

• bent-core
• rod-like
• photochromic
• dimers
• non-symmetrical
• polar group
• nematic phase