Liquid crystalline properties of and intramolecular hydrogen bonding in 4-methyl-2 '-hydroxy-4 '-alkoxyazobenzenes

A homologous series of 4-methyl-2'-hydroxy-4'-alkoxyazobenzenes with chain lengths from 1 to 12 carbon atoms was synthesized and the temperatures of m elting, freezing and transition from nematic to isotropic phase were determ ined. The main thermodynamic characteristics for those transitions were est imated. The liquid crystalline properties were compared with those of homol ogous series without OH groups and show a marked extension of the nematic p hase for the OH substituted compounds. The spectroscopic manifestations of the hydrogen-bonded OH . . .N chelate ring are discussed, based on a compar ison of experimental and Density Functional Theory (DFT) calculated frequen cies and IR intensities. The evolution of the IR absorption in the range 15 40-1660 cm(-1), ascribed to the OH bending vibrations, is presented on goin g from the dilute CCl4 solution through the isotropic and nematic phases to the solid state.