The influence of bromine substitution and linking groups on the phase behaviour of light-responsive rod-like molecules

Abstract

The effect of aromatic core bromination as well as different linking groups on the phase behaviour of light-responsive rod-like liquid crystalline materials is reported. For this purpose, two new series of laterally brominated rod-like molecules are designed and synthesized. The two series have three benzene rings connected using different linking groups either azo or ester units with different directions. Both series have pentyloxy chain at one end and an octyl chain at the other end in the first group or an octyloxy chain in the second group of materials. Additional lateral bromine substituent was inserted at ortho position with respect to the pentyloxy chain. The molecular self-assembly of the new materials was investigated using polarized optical microscope (POM), differential scanning calorimetry (DSC) and X-Ray diffraction (XRD). Depending on the type of the terminal chain (octyl or octyloxy) at one end and nature of the linking groups nematic phases as well as smectic C phases are observed, with variable temperature ranges. Interestingly, the nematic phases were found to exhibit cybotactic clusters with tilted SmC or orthogonal SmA structure (NCybC or NCybA) with wide temperature ranges. Finally, the isothermal photo switching because of cis–trans photoisomerization was investigated in solution as well as between different liquid crystal phases. This report could be of interest for optical information storage device applications.