Synthesis, mesogenic and photoisomerization studies of (E)-4-[(4-pentyloxyphenyl)diazenyl]phenyl alkanoates

Abstract

ABSTRACTHomologous series of esters of (E)-4-[(4-pentyloxyphenyl)diazenyl]phenol and aliphatic carboxylic acids were synthesized, 5O-m for short. Derivatives with alkyl chains longer than seven carbon atoms are described in this article for the first time. The mesogenic properties and phase transition parameters (temperatures and enthalpies) were measured using a polarizing microscopy and a differential scanning calorimetry. Investigated compounds exhibit occurrence of the enantiotropic nematic phase, despite two derivatives with the longest alkyl chains. One can observe two crystalline phases in two derivatives (5O-6, 5O-7). The presence of the azo group in the homologous series of compounds suggests that the possibility of trans–cis isomerization is controlled by light. Such studies have been carried out and their results suggest that the presence of two trans–cis isomerization mechanisms described as the first-order reaction.