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Abstract
Five homologous series of 4-substituted phenyl 4`-(4”-alkoxy phenylazo) benzoates (Ina-e) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 8, 10, 12, 14, and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH₃O, CH₃, H, Br, and CN groups. Compounds prepared were characterized by infrared, mass, and H¹-NMR spectroscopy and their mesophase behavior investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Only for the lower group of compounds, I8a-e, that showed a nematic phase, the nematic-to-isotropic transition temperatures (TN-I) were successfully correlated to the polarizability anisotropy of bonds to the substituent X. A comparative study was made between the investigated compounds and two previously prepared isomeric groups. In the first group of isomers, 4-(4`alkoxy phenylazo) phenyl 4``-substituted benzoates (bna-e), the ester groups are inverted. While in the second, 4-(4`-substituted phenylazo) phenyl 4``- alkoxy benzoates (ana-e), two modifications were made, inversion of the COO group, and exchange of the two wing substituents