Synthesis, characterization of azobenzene and cinnamate ester based calamitic liquid crystalline compounds and their photoresponsive properties

Abstract

A series of azobenzene-containing mesogens end-capped with cinnamoyl esters were synthesized and investigated its mesogenic and photochemical properties. Terminal substituents of the molecules were changed with various substituents like CN, Cl, H, CH3, and OCH3. Liquid crystalline properties of the synthesized compounds were studied and confirmed using differential scanning calorimetry, polarising optical microscopy. Compounds (4a–4e) exhibited a thermotropic mesomorph behaviour viz., nematic and smectic phases that depends on the terminal substituents. The thermal transition temperatures and the mesophase types are depend on the terminal substituents which are ascribed with the increasing cohesive forces between molecules as the conjugation length increases. These photochromic compounds exhibited strong UV–vis absorption maxima between 330 and 340nm. Upon irradiation with selective UV light produces the trans–cis isomerization producing new maxima at 450nm due to cis configuration.