Triphenylene 2, 3-dicarboxylic imides as luminescent liquid crystals: Mesomorphism, optical and electronic properties

A novel small-sized discotic core was constructed by fusing an imide unit with well-known triphenylene core. All target compounds 6a-k self assemble into a liquid crystalline phases having high clearing temperatures and broad phase ranges over 200 °C, and exhibit green luminescence both in solution and solid states. On cooling from the isotropic phase, compounds 6d-e and 6i-j containing the branched N-alkyl chain show only one peak for the isotropic to mesophase transition which is stable down to −50 °C. Comparison of 6a's mesomorphic behaviors and photophysical properties to a known hexahexyloxytriphenylene (1a) and the parent compound (4a) demonstrates the importance of peripherally attached functional groups in stabilizing columnar mesophases and inducing long-wavelength emission. Both the experimental results and computational calculations show that suitable peripheral functionalization of the discotic liquid crystal molecules not only results in significant differences in mesogenic behavior of the molecules, but also renders the molecules with the interesting optoelectronic properties, including large Stokes shifts and low-lying LUMO energy levels.