Highly ordered columnar superlattice nanostructures with improved charge carrier mobility by thermotropic self-assembly of triphenylene-based discotics

A series of triphenylene esters with two ester groups at 2,3-, 2,7-, 2,6- and 3,6- substituent positions was successfully synthesized and fully investigated. Their self-assembly properties were exhaustively examined by DSC, POM, 1DXRD, 2DXRD, SAXS, TEM methods together with EDM and ESP calculations. It was unexpected that the 3,6-substituted triphenylene ester T5E36 formed an uncommonly helical hexagonal columnar superlattice structure made up of 9₁ right-handed helixes with a pitch of 60.3 Å. This helical superlattice structure was further studied by using transmission electron microscopy and the diameter of the T5E36 particles was found to be at the nanometer scale. Ultimately, the bipolar charge carrier mobility was measured by the time-of-flight method to be in the order of 10^-1 cm² V^-1 s^-1. The formation of this helical superlattice nanostructure no doubt improved their electronic properties and made them more attractive in organic electronics.