Study of the effect of hydrogen bonding on the phase behaviour of p-nitro azobenzene derivatives with hydrophilic tails

The infrared spect ra of N-n-(4-nitrophenyl)azophenyloxyalkyldiethanolamine s (Cn) are examined in the range of 4000-400 cm(-1) at different temperatur es and the assignment of the fundamental vibrations given. Based on (1) the localization of the broad absorption band at 3456 cm(-1), and (2) attribut ion of the associated OH bands centred at 1410-1390, 1100, and 650-634 cm(- 1) to, respectively delta OH deformation, nu C-O stretching and gamma OH ou t-of-plane bending, intermolecular hydrogen bonding between OH groups in th e crystalline, liquid crystalline and isotropic states is proposed. By cons idering the results of FTIR, WAXD and DSC measurements, the molecular arran gement of C10 in its smectic A phase as consisting of hydrogen bonding and strong interaction between dipolar groups (NO,) is proposed. This may expla in the high stability and high orientational ordering property of Cn compou nds in the liquid crystalline state compared with that of n-bromo-1-[4-(4-n itrophenyl)azophenyl]oxyalkanes (Bn).