Azoester-based H-shaped symmetrical mesogenic dimers containing – CH₃/–OCH₃ terminal substituent

Abstract

Two extensive homologous series of H-shaped symmetrical dimers were synthesized and their thermotropic properties studied by differential scanning calorimetry and on a hot-stage of a polarizing microscope. These compounds consist of two mesogenic units of azoester interconnected through flexible spacers (n = 4) resulting in the structure of ‘H-shaped’ dimeric compounds. The difference between the two series is in the structure of terminal substituents (–CH₃ for series I and –OCH₃ for series II) attached on the azoester mesogens at one terminus. All these compounds were found to be smectogenic. The effect of different terminal substituents on mesomorphism is discussed. The trans-azobenzene groups of the H-shaped dimeric compounds display a high-intensity π–π* transition at about 365 nm and a low-intensity π–π* transition at around 460 nm, therefore, photochromism can be achieved by the introduction of the azo linkage to the H-shaped dimeric compounds.

Keywords:

• azoester
• H-shaped
• symmetrical dimers
• smectic C
• DSC