Supramolecular interactions of conjugated Zn- and protonated porphyrin polymer with carbon nanotubes

The interaction of a highly soluble conjugated Zn -porphyrin containing polymer with a surface of single-walled carbon nanotubes, producing a soluble polymer-nanotube complex, is reported. We found that successful complexation required the addition of trifluoroacetic acid to the solvent tetrahydrofuran in order to disrupt solvent-porphyrin coordination that prohibits close interaction of the polymer with the nanotube surface. In the presence of trifluoroacetic acid, the complex remained soluble even 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 observed via a 127 nm bathochromic shift of the Q-band absorption in the UV-vis spectrum. In addition, removal of the Zn atoms and protonation of the porphyrin repeat units under acidic conditions resulted in a polycationic polymer that also forms strong interactions with carbon nanotubes which result in soluble supramolecular complexes. Control experiments with the Zn -porphyrin monomer indicated that homogeneous solutions could be prepared by sonication, but the monomer-nanotube interactions were weak and resulted in nanotube precipitation within minutes. Atomic force microscopy and transmission electron microscopy studies indicated that the polymer is capable of exfoliating large nanotube bundles into individual tubes and small bundles that are coated in polymer.