Photoresponsive chiral nanotubes of achiral amphiphilic azobenzene

Abstract

Supramolecular chirality has generally been fabricated by an aggregation process of chiral building blocks. Herein, we report the fabrication of the soft chiral nanotubes by chiral self-assembly, exclusively from a novel designed achiral carboxylic-substituted bolaamphiphilic azobenzene. Based on the studies with UV-vis absorption, circular dichroism (CD), transmission electron microscopy (TEM), and X-ray diffraction (XRD) spectra, a plausible mechanism by which a chirally helical shape emerges from the nonsymmetric packing of an achiral molecule has been proposed. Our results demonstrate a valid approach for correlating the molecular structure to the macroscopic properties, in which, by ingenious molecular design, supramolecular chirality can be achieved from achiral molecular building blocks. It was further revealed that the morphology and chirality of the self-assembled nanostructures change in response to external stimuli such as light and heat. This should open an avenue for a good understanding of the ways in which structural variation affects self-assembled structures at the molecular level. We should also find potential applications as smart carriers for the controlled release and site-specific targeting of the loading, modulated by environmental stimuli.