Carbon Nanotubes Conjugated with Triazole-Based Tetrathiafulvalene-Type Receptors for C-60 Recognition

Fullerene receptors prepared by a twofold Cu-I-catalyzed azide-alkyne cycloaddition reaction with pi-extended tetrathiafulvalene (exTTF) have been covalently linked to single-walled carbon nanotubes and multi-walled carbon nanotubes. The nanoconjugates obtained were characterized by several analytical, spectroscopic and microscopic techniques (TEM, FTIR, Raman, TGA and XPS), and evaluated as C-60 receptors by using UV-Vis spectroscopy. The complexation between the exTTF-triazole receptor in the free state and C-60 was also studied by UV-Vis and H-1 NMR titrations, and compared with analogous triazole-based tweezer-type receptors containing the electron-acceptor 11,11,12,12-tetracyano-9,10-anthraquinodimethane and benzene rings instead of exTTF motifs, providing in all cases very similar values for the association constant (log K-a approximate to 3.0-3.1). Theoretical density functional theory calculations demonstrated that the enhanced interaction between the host and the guest upon increasing the size of the pi-conjugated arms of the tweezer is compensated by an increase in the energy penalty needed to distort the geometry of the host to wrap C-60.