Luminescent assemblies of pyrene-containing bent-core mesogens: liquid crystals, π-gels and nanotubes

Abstract

Bent-shaped molecules incorporating terminal pyrene moieties were designed and synthesized aiming at promoting a variety of luminescent self-assembled materials. The novel compounds are fluorescent both in solution and in condensed phases, achieving brighter fluorescence in the last case with fluorescence quantum yields up to 60%. Depending on the number of pyrene units (1 or 2) and/or the presence or absence of a long and flexible linker between the bent-core and the pyrene structures, bent-core liquid crystal phases, physical gels and nanoassemblies were obtained. Their properties depend on the molecular design, unveiling a synergistic and versatile 'tandem' of the bi-functional system in supramolecular functional materials chemistry. Long hydrocarbon spacers connecting bent-core and pyrene structures were necessary to display mesomorphic properties, achieving monotropic rectangular columnar mesophases, being for one compound stable at room temperature and displaying a glassy transition below room temperature, as revealed by POM, DSC and XRD. Liquid crystal phases exhibited excimer-like emission. In addition, organogels were obtained without the help of hydrogen bonding functionalities, exhibiting in one case supergelator behavior. Different nanoassemblies were obtained from these non-amphiphilic bent-core structures, in particular unprecedented organic nanotubes with beveled ends formed by a single bilayer.