Helical hexagonal columnar superlattice structures with high charge carrier mobility formed by hierarchical self-assembly of 3,6-substituted triphenylene esters

Abstract

The self-assembly of discotic liquid crystals into ordered supramolecular structures provides a fascinating approach for creating photoelectric semiconductive materials. In this work, the synthesis and characterization of a series of triphenylene derivatives (T5E36-n, n = 2–7) containing ester groups at 3,6-substituted positions are reported on the basis of comprehensive investigations by using DSC, POM, 1DXRD, 2DXRD, and TEM methods together with EDM and DFT calculations. Compounds with the ester chains of an even number of carbon atoms exhibited unprecedented helical hexagonal columnar superlattices composed of 8₁ right-handed helixes with pitch lengths of 35–37 Å, and the superlattice structure can be confirmed by combining the diffraction spots at the innermost part of the 2D XRD diffraction patterns and the occurrence of moiré fringes in TEM images. The charge carrier mobilities of the compounds in the helical hexagonal columnar phases reached up to 10⁻² cm² V⁻¹ s⁻¹, which are found to be an order of magnitude higher than those in the normal hexagonal columnar phases. The formation of the helical hexagonal columnar superlattice structures in discotic liquid crystals enhanced the charge transport properties and made them more attractive in organic electronics. This work demonstrated a pathway to precisely control self-assembly in discotic liquid crystals through judicious molecular design and synthesis.