Covalent functionalization of short, single-wall carbon nanotubes: Photophysics of 2,4,6-triphenylpyrylium attached to the nanotube walls

2,4,6-Triarylpyrylium units (TP⁺) have been attached covalently to the walls of short, water-soluble single-wall carbon nanotubes (sSWNT) to give TP-sSWNT sample (6.8 wt % on TP⁺). The high loading achieved in this manner has allowed characterization of the material by a wide range of techniques, including AFM (about 1 μm length), thermogravimetric analyses (absence of inorganic particles in the sample), Raman spectroscopy (radial breathing vibration mode at 180 cm^-1), and solution ¹H NMR spectroscopy (up to 0.5 ppm variation in the δ of the protons upon attachment to the graphene walls). Optical spectroscopy reveals the absence of the van Hove singularities in the TP-sSWNT sample. Fluorescence spectroscopy indicates sSWNT quenching of the otherwise intense TP⁺ emission. Laser flash photolysis has allowed detecting a transient species characterized by a broad absorption from 400 to 700 nm that decays with a fast (<500 ns) and a slow (a few microsecond) kinetics. TP-sSWNT emits NIR luminescence with an estimated 2.3 × 10^-3 quantum yield.