Vibrational Spectra of Liquid Crystals. I. Changes in the Infrared Spectrum at the Crystal–Nematic Transition

The infrared spectra of 4,4′-bis(alkoxy) azoxybenzenes (methyl, ethyl, butyl, pentyl, and hexyl) have been examined as a function of temperature through the crystal–nematic transition. Several bands are observed to disappear gradually as this transition is approached. The nature of these vibrational modes and the relative rates of their disappearance are discussed in terms of a lattice defect model of the crystal–nematic transition. Preliminary results for the crystal–smectic transition in 4,4′bis(heptyloxy) azoxybenzene are also reported.