Pillar[5]arene-Decorated Single-Walled Carbon Nanotubes

Abstract

Control\nof single-walled carbon nanotube dispersion properties is of substantial\ninterest to the scientific community. In this work, we sought to investigate\nthe effect of a macrocycle, pillar[5]­arene, on the dispersion properties\nof a polymer–nanotube complex. Pillar[5]­arenes are a class\nof electron-rich macrocyclic hosts capable of forming inclusion complexes\nwith electron-poor guests, such as alkyl nitriles. A hydroxyl-functionalized\npillar[5]­arene derivative was coupled to the alkyl bromide side chains\nof a polyfluorene, which was then used to coat the surface of single-walled\ncarbon nanotubes. Noncovalent functionalization of carbon nanotubes\nwith the macrocycle-containing conjugated polymer significantly enhanced\nnanotube solubility, resulting in dark and concentrated nanotube dispersions\n(600 μg mL^–1), as evidenced by UV–vis–NIR\nspectroscopy and thermogravimetric analysis. Differentiation of semiconducting\nand metallic single-walled carbon nanotube species was analyzed by\na combination of UV–vis–NIR, Raman, and fluorescence\nspectroscopy. Raman spectroscopy confirmed that the concentrated nanotube\ndispersion produced by the macrocycle-containing polymer was due to\nwell-exfoliated nanotubes, rather than bundle formation. The polymer–nanotube\ndispersion was investigated using ¹H NMR spectroscopy,\nand it was found that host–guest chemistry between pillar[5]­arene\nand 1,6-dicyanohexane occurred in the presence of the polymer–nanotube\ncomplex. Utilizing the host–guest capability of pillar[5]­arene,\nthe polymer–nanotube complex was incorporated into a supramolecular\norganogel.