TNF Induced Switching of Columnar Rectangular to Hexagonal Assemblies in a New Class of Triphenylene-Based Room Temperature Discotic Liquid Crystals.

Abstract

A straightforward synthesis of triphenylene-based oligomeric systems that self-organize into room temperature columnar structures is presented. The compounds with longer spacer length (m = 10 and 12) exhibit columnar rectangular (Colr) mesophase whereas the compound with m = 8 exists in glassy Colr state. Interestingly, the Colr self-assembly of these compounds switches to columnar hexagonal (Colh) on doping the compounds with 2,4,7-trinitrofluorenone (TNF). For the dopant concentration of 1:1 with respect to native compound, an intermediate transition state between Colr and Colh phase was observed which completely transformed into the hexagonal phase on increasing the concentration to 1:2 (compound: TNF) and afterward. Both the Colr and Colh self-assemblies have been well resolved by detailed X-ray analysis. These kind of oligomeric compounds generally possess a combination of desirable alignment properties analogous to monomeric compounds and long-lived glassy states similar to that of polymeric mesogens. In addition, charge hopping behavior is expected to increase in these compounds due to donor-acceptor interactions. Overall, these compounds can find possible potential applications in semiconductor devices.