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 mu m length), thermogravimetric analyses (absence of inorganic particles in the sample), Raman spectroscopy (radial breathing vibration mode at 180 cm(-1)), and solution H-1 NMR spectroscopy (up to 0.5 ppm variation in the delta 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 x 10(-3) quantum yield.