Supramolecular Self-Organization of Fullerene Derivatives in Solutions Studied by Pulsed Field Gradient NMR Technique

Self-organization of a series of differently functionalized fullerene derivatives in solvents of different polarity was investigated by pulsed field gradient nuclear magnetic resonance on 1H, 19F and 31P nuclei. The hydrodynamic diameters were calculated for each fullerene derivative-solvent system on the basis of Stokes–Einstein model. It was shown that fullerene derivatives comprising no polar groups do not undergo any noticeable aggregation in carbon bisulfide, deutereted chloroform and toluene-d8. The particle diameters of 1.2–1.4 nm revealed for these solutions were very close to the van der Waals diameter of the fullerene derivative molecules. The fullerene derivatives comprising polar –COOH, –COOK and –P(O)(OH)2 groups appended to the carbon cage undergo self-assembling in solutions. The diameters of the formed clusters varied from 2.2 to 9.6 nm depending on the solvent and the temperature. The strongest tendency to self-assembling was revealed for water soluble fullerene derivatives in aqueous solutions where, presumably, water molecules are also incorporated in the structure of the clusters.