Influence of monohalogenated flexible tails on the mesomorphism of triphenylene-based discotics

Abstract

A series of triphenylene-based discotic liquid crystals (DLCs) modified by fluorination or chlorination at the end of peripheral flexible chains were examined in this work. DLC derivatives containing one mono fluorine or chlorine-substituted flexible chain 4a-e and six mono fluorine or chlorine-substituted flexible chains 8a & 8b, 10a & 10b were mainly synthesized and molecular structures confirmed by 1H NMR, 19F NMR and MALDI-TOF MS. The mesogenic properties of the obtained compounds were further studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD). Impressively, compounds 4a-e were found exhibiting hexagonal columnar phases and the π-π stacking distances of 4a-e were lower than that of the parent molecule HAT5. Due to the influence of atomic radius and molecular symmetry, the mesophase stability of the fluorinated triphenylene compounds was greater than the chlorinated ones. Through the modification of the side chain, the self-assembly behavior of triphenylene was stronger and the intracolumnar distance was decreased, which may give rise to a higher charge transport mobility. Compound 10b showed self-assembly behavior and formed a spherulite texture that could also remain orderly until room temperature. This is rare in reported DLCs and it might be applied as active components of in electronic devices. These ordered stacked discotic molecules may exhibit improved charge carrier mobility as semiconducting materials.