Triphenylene trimeric discotic liquid crystals: synthesis, columnar mesophase and photophysical properties

Abstract

Discotic liquid crystal materials, as organic semiconductor materials, have demonstrated tremendous prospective applications in high-tech fields such as solar cells and organic light-emitting diodes (OLEDs). Discotic liquid crystals represented by triphenylene have been extensively researched for their highly ordered self-assembly and self-repairing capabilities. The triphenylene motif, commonly introduced into trimeric discotic molecules as an electron donor, was relatively rare when used as a repeating unit in trimeric discotic liquid crystals. In comparison with triphenylene monomers and dimers, the long-chain-linked triphenylene trimers did not exhibit differentiated mesomorphic properties. In this study, we synthesized a series of triphenylene–triphenylene–triphenylene type discotic liquid crystalline trimers TTPn through Suzuki–Miyaura cross-coupling reaction, connected via σ single bonds. Compared with the triphenylene monomers and their dimers, TTPn demonstrates unique and superior qualities in terms of mesomorphic and photophysical properties. The series of compounds exhibits oblique discotic columnar phases with a broad mesophase range. The TTPn showed blue photo-induced luminescence in solution, with the highest absolute fluorescence quantum yield reaching 66% in solution, and the photoluminescence phenomenon still exists in the film state. Therefore, the TTPn holds potential application value in fields such as liquid crystalline semiconductors and organic light-emitting diodes.