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

ABSTRACT

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.

GRAPHICAL ABSTRACT

KEYWORDS:

• HAT6
• discotic liquid crystals
• Raman spectroscopy
• electrical conductivity
• DFT simulation
• band gap

Acknowledgements

The authors acknowledge the Fundamental Research Grant Scheme (FRGS) under Grant FP064-2016 and University of Malaya Postgraduate Research Grant (PPP) – Research under Grant PG118-2016A for funding this work. O.M. acknowledges support from NSERC Canada (Discovery Grants and SPG Grants), Canada Research Chairs, Fondation de l’École Polytechnique de Montréal and Canada Foundation for Innovation (CFI). We also acknowledge the useful discussions with Dr Abhijit Chatterjee of Dassault Systemes Biovia K.K. on the modelling aspect of this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors acknowledge the Fundamental Research Grant Scheme (FRGS) under Grant FP064-2016 and University of Malaya Postgraduate Research Grant (PPP) – Research under Grant PG118-2016A for funding this work. O.M. acknowledges support from NSERC Canada (Discovery Grants and SPG Grants), Canada Research Chairs, Fondation de l’École Polytechnique de Montréal and Canada Foundation for Innovation (CFI).