Mesomorphic Behavior of 1,2-Phenylene Bis[4-(4-alkoxybenzylideneamino)benzoates

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Abstract
A series of 1,2-phenylene bis[4-(4-alkoxybenzylideneamino)benzoates has been prepared in order to establish that the nonlinear molecular structure is not necessarily incompatible with mesophase formation. The phases appearing in the methoxy and ethoxy derivatives are classical nematic. While the propoxy to octyloxy derivatives display a smectic A phase, as well as a nematic phase, the higher homologous members are purely smectogenic. Although the introduction of a methyl group to the 3-position of the central phenylene ring eliminates the nematic phase, the thermal stability of the smectic A phase is not much affected. The 4-methylation promotes both the nematic and smectic A phases. A metastable smectic B phase is observed in many members of these three series. The above-mentioned behavior closely resembles that given by the corresponding methyl derivative of phenyl 4-(4-alkoxybenzylideneamino)benzoate.