Synthesis, Characterization and Determination of Mesophase Transition of Azo-azomethine Derivatives with Different Terminal Chain Lengths

Six new azo-azomethinederivatives were successfully synthesizedand characterized. These derivatives, 5a-fwere differentiated by a variety of different terminal lengthssuch as pentyl, heptyl, nonyl and dodecyl chains. The experiment started with the reaction of p-nitroaniline with phenol,forming4-(4-nitrophenylazo)-phenol, 1. Alkylation of 1with pentyl, nonyl and dodecylbromide gave(4-nitrophenyl)-4(4-alkoxyphenyl)-diazene, 2a-c. These nitro intermediates,2a-cwere reduced to afford intermediates 3a-c, 4-(4-alkoxy-phenylazo)-phenylamine. Alkylation reaction of p-hydroxybenzaldehyde with heptyl and dodecylbromide gave intermediates 4a-b, 4-alkoxybenzaldehyde. Cross condensation reactions of 3a-c and 4a-bgave sixcompounds, 5a-f, with azo and Schiff base linking units but with different chain lengthsat both terminal positions. All the compounds were characterizedusing Fourier Transform Infrared spectroscopy (FT-IR), 1H and 13C Nuclear Magnetic Resonance spectroscopy (NMR) and CHN elemental analysis. The mesophase transitions of these compounds were determined using PolarizedOptical Microscope (POM).It was observed that compounds 5b, 5c,5d, 5eand 5fwere mesogenic while compound 5awas not mesogenic. The transition temperature of the compounds having mesophase behaviour were further confirmed using DSC. All the DSC thermograms showed good agreement with the phase transition observed under POM. The study on the structure-properties relationship was conducted in order to determine the effect of the terminal group, length of the chains andlinking units to the mesophase behaviour of the compounds.