Supramolecular Functionalization of Single-Walled Carbon Nanotubes (SWNTs) with a Photoisomerizable Conjugated Polymer

A fluorene- and azobenzene-containing conjugated polymer, poly[2,7-(9,9-didodecylfluorene)-alt-4,4′-azobenzene] (F12AZO) has been successfully synthesized using Suzuki polycondensation. The introduction of two dodecyl chains on the flourene unit resulted in a highly soluble polymer. F12AZO possesses excellent thermal stability, with a decomposition temperature over 400 °C under Ar. The reversible photoisomerization of the azobenzene units was achieved upon alternating photoirradiation with light of wavelength less than 450 nm (cis-form), and light in the range of 450–600 nm (trans-form). The supramolecular complex formation of trans-F12AZO, and cis-F12AZO with single-walled carbon nanotubes (SWNTs) has been studied, and it was found that this polymer can form very strong supramolecular polymer-nanotube assemblies. Furthermore, the trans and cis isomers of F12AZO enable the selective dispersal of individual SWNTs in toluene or THF, and the selectivity of the SWNTs is strongly dependent on the solvent, as well as the type of isomer used. UV–vis–NIR, and photoluminescence–excitation spectroscopy (PLE) were used for the characterization and identification of the nanotube species that are solubilized and exfoliated by this polymer.