Large core-expanded triazatruxene-based discotic liquid crystals: synthesis, characterization and physical properties

Abstract

Two new discotic liquid crystals based on the triazatruxene core, TAT-1 and TAT-2, have been constructed using diamine–diketone condensation as the key expansion step with different solubilizing chains attached at the periphery. The new mesogens possess good thermal stability and show columnar liquid crystalline properties. Upon expansion of the core size, TAT-2 is found to have a strong tendency to aggregate both in solution and in thin film. Their optical properties, electronic properties and thermal behaviour are investigated by various techniques. They are found to respond to protons due to protonation of the pyrazine rings in the conjugation system and an obvious colour change is observed upon protonation. These new molecules are also found to possess a weak intramolecular charge transfer (ICT) nature and a weak ICT band can be observed on the UV-vis absorption spectra. The charge transport properties of TAT-1 and TAT-2 have been measured by a space-charge limited-current technique and the highest mobilities obtained for TAT-1 and TAT-2 are 0.14 cm² V⁻¹ s⁻¹ and 0.69 cm² V⁻¹ s⁻¹, respectively.