Molecular structure of the Discotic Liquid Crystalline Phase of Hexa-peri-Hexabenzocoronene/Oligothiophene Hybrid and their Charge Transport properties

TL;DR

This study uses molecular dynamics simulations to analyze the molecular structure and charge transport properties of a novel discotic liquid crystalline phase based on HBC and oligothiophene units, relevant for organic electronics.

Contribution

It provides detailed molecular-level insights into the structure and charge mobility of a new HBC-based liquid crystal phase, confirmed by experimental data and simulations.

Findings

Hexagonal columnar arrangement confirmed by simulations.

Average molecular twist of 25 degrees and tilt angle of 43 degrees.

Charge mobility depends on molecular twist and spacing.

Abstract

Using atomistic molecular dynamics simulation we study the discotic columnar liquid crystalline (LC) phases formed by a new organic compound having Hexa-peri-Hexabenzocoronene (HBC) core with six pendant oligothiophene units recently synthesized by Nan Hu et al. (N. Hu, R. Shao, Y. Shen, D. Chen, N. A. Clark and D. M. Walba, Adv. Mater. 26, 2066, 2014). This HBC core based LC phase was shown to have electric field responsive behavior and has important application in organic electronics. Our simulation results confirm the hexagonal arrangement of columnar LC phase with a lattice spacing consistent with that obtained from small angle X-ray diffraction data. We have also calculated various positional and orientational correlation functions to characterize the ordering of the molecules in the columnar arrangement. The molecules in a column are arranged with an average twist of 25 degrees having an average inter-molecular separation of ~5 {\AA}. Interestingly, we find an overall tilt angle of 43 degrees between the columnar axis and HBC core. We also simulate the charge transport through this columnar phase and report the numerical value of charge carrier mobility for this liquid crystal phase. The charge carrier mobility is strongly influenced by the twist angle and average spacing of the molecules in the column.