Binding of rigid dendritic ruthenium complexes to carbon nanotubes

Single-walled carbon nanotubes (SWNTs) bind strongly to rigid ruthenium metallodendrimers. High valence ions effectively coagulate these nanotubes from stable dispersions in N, N-dimethylforamide. While ruthenium salts and small [Ru(diimine)(3)](2+) complexes also coagulate the nanotubes, they require much higher concentrations and are easily extracted from the nanotubes with acetonitrile. Enantiomerically pure ruthenium metallodendrimer [Lambda(6)Lambda(3)Lambda- Ru-10](20+)[PF6-](20) is shown to bind strongly and specifically to the SWNTs. Most of the nanotube's ends are functionalized with this large (5.8 nm), optically active, rigid supramolecular complex. We study the binding capacity with UV-vis and atomic absorption spectroscopy. Imaging the functionalized nanotubes with scanning electron microscopy and atomic force microscopy (AFM) yields direct confirmation of end functionalization. Statistical analysis of the AFM images shows the morphology of the functionalized ends is consistent with the nanotubes binding to one of the endo- or exoreceptors around the dendrimer. Implications of these results toward efficient nanomanufacturing of carbon nanotube devices are discussed.