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

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.     

Calorimetric study of the cubic mesogen,ACBC(16)

The heat capacity of the cubic mesogen ACBC(16) was measured between 16 and 500?K by adiabatic calorimetry. As well as the known condensed phases, a new crystalline phase was found to undergo a glass transition at around 165?K. Phase transitions between crystal, SmC, cubic, and isotropic liquid phases took place at 399.16, 431.15, and 474.30?K, respectively. As in the case of ANBC, a broad hump was observed in the heat capacity of the isotropic liquid phase. The first order nature of the SmC–cubic phase transition was confirmed for the first time by the observation of supercooling of the cubic phase. The broad hump in the isotropic liquid phase was shown to extend to a low temperature side if the isotropic liquid was supercooled, suggesting that the event occurring at the hump is not directly related to the cubic–isotropic liquid phase transition.