Polarized infrared spectra of 4-chloro-2'-hydroxy-4'-hexyloxyazobenzene were studied from 25 to 120 degrees C encompassing transitions from the crystalline to the isotropic phase. The behavior of the nu(OH), delta(OH), and gamma(OH) bands is analyzed. Based on the DFT calculations and on linear dichroism spectroscopy, it was concluded that the core-to-core interaction between hydrogen-bonded chelate rings is responsible for changes in intensity and shape of the bands. A pseudo-band at ca. 620 cm (1) is discussed based on Fermi resonance between the nu(OH) and gamma(OH) modes. A general analysis is presented with respect to the directions of the transition moments of the particular modes. (C) 2009 Elsevier B. V. All rights reserved.