Dodecylated Large Fullerenes: An Unusual Class of Solids

Abstract

The large fullerenes that are formed during the synthesis of C60 by the arc discharge technique can be solubilized by reductive alkylation. The mass range of dodecylated large fullerenes determined by laser desorption ionization, time-of-flight mass spectrometry was found to be 650−3500 amu. The solubility of the dodecylated large fullerenes in chloroform is 15.7 g/L as measured by near-infrared spectroscopy. High-resolution transmission electron microscopy images show the expected nontubular, ring-shaped contrast resembling large fullerenes attached to dodecyl groups. The dodecylated large fullerenes have distinctly different behavior than regular organic molecules in dipolar dephasing, magic angle spinning nuclear magnetic resonance (13C MAS NMR) experiments. Thermal gravimetric analysis and 13C MAS NMR experiments indicate that there is 1 dodecyl group for every 23 sp2 fullerene carbon atoms, that the quaternary aliphatic carbons generated upon dodecylation give signals considerably more shielded than those in alkylated C60 and C70 but similar to the quaternary aliphatic signals in dodecylated single-walled carbon nanotubes, and that the dodecyl groups in the dodecylated large fullerenes exhibit widely varying degrees of motional freedom. The last characteristic was unexpected and apparently results from a combination of dodecyl groups in void spaces of varying size and dodecyl groups on molecules that tumble at various rates.