Formation of Highly Luminescent Supramolecular Architectures Possessing Columnar Order from Octupolar Oxadiazole Derivatives: Hierarchical Self-Assembly from Nanospheres to Fibrous Gels

The synthesis and study of the liquid crystalline, photophysical, and aggregation behavior of novel octupolar oxadiazole derivatives are reported. These molecules formed columnar mesophases at elevated temperatures Which transformed into a glassy state at ambient temperatures wherein the columnar order was retained. Their spontaneous concentration dependent hierarchical self-assembly from spheres to fibrous gels has been investigated using TEM, SEM, and XRD. Retention of the hexagonal column (Col(h)) order was also observed in the fibrous aggregates. Concentration dependent luminescence spectral studies indicated that the change in morphology from spheres to fibrous aggregates was associated with a shift in chromophore packing from predominantly H-type to J-type aggregates. Time resolved anisotropic investigations revealed that the columnar stacking of molecules in the aggregated state provided a pathway for excitation energy migration to the lower energy J-traps.