In Spectroscopic Study of the Electric Field Induced Phase Transition of a Ferroelectrically Switchable Columnar Dibenzopyrene

Abstract

Fourier transform infrared spectroscopy of a ferroelectrically switchable columnar liquid crystalline dibenzopyrene has been performed in the wavenumber range of 450-4000 cm⁻¹ as a function of temperature and applied electric field. The sample was edge-on aligned by the electric field. At 10 V/μm, a Sudden change of the C=O band intensity is observed, whereas no strong field dependence of the aromatic bands was detected. Earlier electrooptical observations evidenced a phase transition at this field strength. The temperature dependence of the intensities reveals a preferential orientation of the aromatic cores parallel to the direction of the electric field in the columnar phase. This orientation vanishes when heating into the isotropic liquid. The temperature dependence of the C=O band frequency is similar to the behaviour reported for smectic phases of calamitic molecules.