The bottom-up synthesis of tubular nanostructures with specific composition, morphology and chirality is still an open challenge in nanoscience. Takuzo Aida, Takanori Fukushima, Wusong Jin and colleagues now describe a synthetic protocol for controlling the number of walls of a class of supramolecular nanotubes.
The researchers — who are based at RIKEN, the Tokyo Institute of Technology, and Donghua University — start from a hexabenzocoronene molecule to which they attach two alkyl chains on one side and two perfluorinated chains on the other side. In methylene chloride and at low concentration, the molecule self-assembles into single-walled tubular nanostructures. Through spectroscopic analysis, the team discerned that the nanotube walls adopt a bilayer morphology: the coronene units are stacked to form aggregates in the core and held together by the alkyl chains; the perfluorinated chains extend radially towards the bulk solvent and the inner part of the tube.
When the concentration of the molecule was increased, Aida and colleagues observed the formation of double- and multiwalled nanotubes in a stepwise fashion. Remarkably, the transformation to a higher number of walls goes through an intermediate morphology in which a coiled supramolecular structure self-assembles around the parent nanotube. The researchers also suggest that the ability to build nanotubes one wall at a time could be exploited to functionalize each wall selectively for more complex functional nanostructures.