Noncovalent functionalization and solubilization of carbon nanotubes by using a conjugated Zn-porphyrin polymer

A highly soluble, conjugated Zn-porphyrin polymer was synthesized and found to strongly interact with the surface of single-walled carbon nanotubes, producing a soluble polymer-nanotube complex. Successful complexation required the addition of trifluoroacetic acid to the solvent (THF). It was found that the complex remained soluble after excess free polymer was removed from solution, and could be centrifuged at high speed with no observable sedimentation. Furthermore, the polymer-nanotube assembly resulted in enhanced planarization and conjugation within the porphyrin polymer, which was manifested in a 127 nm bathochromic shift of the Q-band absorption. Control experiments with the Zn-porphyrin monomer indicated that homogeneous solutions could be prepared by means of sonication, but the monomer-nanotube interactions were significantly weaker, leading to nanotube precipitation within minutes. Atomic force microscopy (AFM) studies indicated that the polymer enables exfoliation of nanotube bundles and is able to "stitch" multiple nanotubes together into a series of long, interconnected strands.