The influence of bromine substitution and linking groups on the phase behaviour of light-responsive rod-like molecules
Mohamed Alaasar, Tejal Nirgude, Christian Anders
Abstract
• New light responsive rod-like liquid crystals are reported. • The phase behaviour was characterized by DSC, POM and XRD. • The effect of lateral bromination as well as different linking units was investigated. • Wide ranges of cybotactic nematic phases are reported. • The materials undergo fast and reversible photoinduced phase transition. 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 (N CybC or N CybA ) 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.