Mesomorphic Properties of 4-azobenzenes and Related Compounds

Article abstract of DOI:10.1246/bcsj.64.2192

The mesomorphic properties of a homologous series of 4-<3,4-bis(4-alkoxybenzoyloxy)benzylideneamino>azobenzenes have been studied by differential scanning calorimetry and microscopy.While the nematic phases exhibited by the ethoxy and propoxy homologues are metastable, those exhibited by all of the butoxy-to-hexadecyloxy homologues exhibit the temperature range of stable existence.A metastable smectic A-phase is observed for the tetradecyloxy and hexadecyloxy homologues.Among the examined 4-<2,4-bis(4-alkoxybenzoyloxy)benzylideneamino>azobenzenes, only the dodecyloxy and tetradecyloxy members are nematogenic.Their clearing points are located at more than 30 deg C below the melting points. 4-(Benzylideneamino)azobenzene and its 3-(4-dodecyloxybenzoyloxy) derivative are nonmesogenic; however, the phase diagrams of binary systems with 4-(4-nonyloxybenzylideneamino)azobenzene revealed that the addition of a 3-(4-dodecyloxybenzoyloxy) group to the former molecule depresses the virtual nematic behavior, but promotes the smectic A behavior.A further addition of the same group at the 4-position drastically raises the nematic-isotropic transition temperature.