Hierarchical Assembly of an Achiral π-Conjugated Molecule into a Chiral Nanotube through the Air/Water Interface

An achiral pi-conjugated fluorinated fused pyrazine derivative has been spread at the air/water interface, and its assembling property is investigated. It has been found that the compound, although without any long alkyl chain, could be spread as a floating film on water surface, the surface pressure of which can be compressed up to ca. 70 mN/m. An inflection point has been observed in the isotherm of the floating film on water surface. The atomic force microscope (AFM), scanning electron microscope (SEM) as well as the transmission electron microscope (TEM) observations revealed that the floating film first formed a multilayer structure and then was compressed into nanotubes after the inflection region as a result of the rolling of the ultrathin film. Interestingly, the rolled nanotubes show circular dichroism although the molecule itself is an achiral species, suggesting the chiral nanotube is predominantly produced on the water surface. The investigation provides an effective way to fabricate supramolecular-based organic chiral nanotubes through an interfacial supramolecular assembly process.