Mesomorphic Properties of 4-[3,4-Bis(4-alkoxybenzoyloxy)benzylideneamino]azobenzenes and Related Compounds

Abstract

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 °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.