Morphological Control of One-Dimensional Nanostructures of T-Shaped Asymmetric Bisphenazine

This paper presents the morphological control of self-assembled structures derived from a novel T-shaped bisphenazine containing cyanophenyl groups. The pi-aggregation of the molecule in solution was verified with H-1 NMR at various concentrations. Self-assembly using a phase transfer method showed morphological transformation from straight strands to flexible nanofibers with significant bundling and coiling, and finally, flat nanofibers with less bundling as solution concentration increased, which was extensively characterized by scanning electron microscopy (SEM). UV-vis spectroscopy in a binary solvent and solid state showed red-shifted absorption with increased absorbance at the long wavelength shoulder region when compared to that in the solution state. A variable temperature UV-vis experiment verified that the spectral change was caused by pi-aggregation. X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy of the assembled structures showed that intermolecular cyano interactions are the major driving force for the formation of the nanofibers while pi-pi interactions are dominant for the straight strands. The increased water contact angle (WCA) of nanofiber films in comparison to a spin-coated film is indicative of the nanoscale surface roughness and the hydrophobic nature of the nanofibers. This report provides a useful design tool based on the rational utilization of cyanophenyl groups in a large pi-core to modulate assembly morphology.