Studies on relation between columnar order and electrical conductivity in HAT6 discotic liquid crystals using temperature-dependent Raman spectroscopy and DFT calculations

The vibrational property of 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6) discotic liquid crystal (DLC) material is investigated in this research by using temperature-dependent Raman spectroscopy technique. One-dimensional (1D) charge transport mechanism in the DLC molecules is enabled in the columnar liquid crystalline (D_h) phase. The result indicates a high core-to-core correlation in the liquid crystal columnar phase, which has a ‘memory’ like effect that extends into isotropic phase at femtosecond timescale. This correlation is also confirmed through electrical conductivity measurement of DLCs, in which the electrical conductivity is enhanced in the DLC phase. DFT simulation was also carried out in order to elucidate the basic properties of HAT6 such as the band gap in the light of Raman spectra. An interesting outcome is that a freely unspecified boundary model produces in a more flexible molecule, resulting in a reduced band gap. Thus, this work provides an understanding of relationship between columnar order and electrical conductivity of HAT6 molecule, and potential strategy for design of DLCs in electronics application.