Liquid Crystals VII. The Mesomorphic Behavior of Homologous: p -Alkoxy- p '-Acyloxyazoxybenzenes

In a continued effort to synthesize compounds which exhibit nematic mesomorphism at room temperature, homologous p-alkoxy-p'-acyloxyazobenzenes and p-alkoxy-p'-acyloxyazoxybenzenes were prepared. The p-substituted groups were normal alkyl chains containing from one to seven carbon atoms. Of the 98 compounds which were prepared in both the azo and azoxy series, 87 exhibited enantiotropic and 3 monotropic nematic properties while only 8 showed smectic behavior. The azoxy “compounds” were generally lower melting than the azo compounds. This is presumably due to the fact that the former are mixtures of isomers (oxygen may be on nitrogen attached to the alkoxyphenyl group or on nitrogen attached to the acyloxyphenyl group). The higher nematic thermal stability of the azoxy materials compared to the azo compounds and to analogous Schiff base compounds may be attributed to broadening of the molecule as a result of the presence of a lateral oxygen atom. This would have the effect of increasing the terminal to lateral interactions.