The role of H-bonded chelate rings in the organization of liquid crystalline 2-hydroxyazobenzenes

Polarized infrared spectra of 4-chloro-2′-hydroxy-4′-hexyloxyazobenzene were studied from 25 to 120 °C encompassing transitions from the crystalline to the isotropic phase. The behavior of the ν(OH), δ(OH), and γ(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 ν(OH) and γ(OH) modes. A general analysis is presented with respect to the directions of the transition moments of the particular modes.