Making Carbon Nanotube Rotaxanes

Single-walled carbon nanotubes (SWNTs) are a promising base for organic electronics, but attempts to add components to the structures to gain additional functions can change the material’s electronic properties by saturating desirable carbon-carbon double bonds. A team led by Emilio M. Pérez of Madrid Institute for Advanced Studies in Nanoscience, in Spain, has developed a strategy for tying a macrocycle around a SWNT, like a ring on a very long finger. The new rotaxane would permit useful components to be chemically attached to the macrocycle, thereby bringing them in the vicinity of the nanotube’s surface but without covalently altering it (Angew. Chem. Int. Ed. 2014, DOI: 10.1002/anie.201402258). To design a linear precursor that would recognize a SWNT and cyclize into a macrocycle, the team began with two tetrathiafulvalene derivatives, which are known to associate with SWNTs. Then, by calculating the circumference around typical SWNTs, the team toggled the length of the linear precursor by adding alkene spacers. Finally, the linear precursor was cyclized through ring-closing metathesis. The chemists showed that the macrocycles don’t change the electronic properties of the SWNTs and cannot be removed unless heated to 360 °C.