Enhanced conductivity and dielectric absorption in discotic liquid crystalline columnar phases of a vanadyl complex

Abstract

A liquid crystalline vanadyl complex has been studied by DSC, polarizing optical microscopy, the reversal current technique, X-ray diffraction and frequency domain dielectric spectroscopy. The compound exhibits three columnar phases: rectangular ordered (Col_ro), rectangular disordered (Col_rd), and hexagonal disordered (Col_hd), all of which show a dielectric relaxation process at low frequencies. In the Col_ro low temperature phase this process seems to be connected with a slow relaxation of polarized polymeric chains inside the columns (mHz frequency range). However, in the Col_hd high temperature disordered phase this relaxation is faster (Hz range). It is interesting that the liquid crystalline phases studied show enhanced conductivity which changes by four orders of magnitude from 10⁻⁹ S m⁻¹ in the orientationally disordered crystal (an ODIC phase) to 10⁻⁵ S m⁻¹ in the Col_hd high temperature phase. Such a value of the conductivity is typical for semiconducting materials.