H-shaped azoester-oxymethylene containing twin liquid crystalline compounds

Abstract

Two mesogenic homologous series of H-shaped symmetrical dimers were synthesised and their thermotropic properties studied by differential scanning calorimetry and on a hot-stage of a polarising microscope. These compounds consisted of two mesogenic units of azoester interconnected through tetramethylene flexible spacers (n = 4) by ether linkage resulting in the structure of ‘H-shaped’ dimeric compounds. The difference between the two series was in the structure of terminal substituents (–CH3 for series I and –OCH3 for series II) attached on the azoestermesogens at one terminus. All these compounds were found to be smectogenic. The mesomorphic properties of the series were compared with each other and with other structurally related mesogenic H-shaped dimers. The trans-azobenzene groups of the H-shaped dimeric compounds displayed a high-intensity π–π ∗ transition at about 365 nm and a low intensity π–π ∗ transition at around 470 nm, therefore photochromism can be achieved by the introduction of the azo linkage to the H-shaped dimeric compounds.