Supramolecular Functionalization of Single-Walled Carbon Nanotubes with Triply Fused Porphyrin Dimers: A Study of Structure-Property Relationships

A triply fused porphyrin dimer bearing long alkyl chains for enhanced solubility was prepared and investigated for its ability to supramolecularly functionalize single-walled carbon nanotubes. It was found that this porphyrin dimer indeed binds strongly to the nanotube surface, allowing the removal of excess unbound porphyrin from solution without diminishing nanotube solubility. UV-vis spectroscopy indicated a bathochromic shift of the porphyrin Soret band upon binding to the nanotube surface, while Raman spectroscopy indicated that functionalization with the porphyrin dimer does not lead to any defects being formed on the nanotube wall. Transmission electron microscopy revealed the presence of individual nanotubes and small nanotube bundles that were heavily coated with porphyrin dimers. Comparison to analogous fused dimers bearing tert-butyl groups for solubility clearly demonstrated that long alkyl chains are necessary for prolonged solution stability of the nanotube complexes. While a previously investigated tert-butyl derivative was found to bind to the nanotube surface, the resulting complex precipitated out of solution within minutes. It was also found that the position of bulky substituents on the porphyrin dimer had a dramatic effect on whether it was able to interact with the nanotube surface.