Phenomena and processes related to the behavior of fullerenes in solutions are reviewed. Data on the solubility of C 60 and C 70 fullerenes in a large number of solvents at various temperatures are presented as well as on diffusion coefficient of fullerenes in solutions. The relation between the factors controlling the behavior of dissolved fullerenes and the clustering tendency they show is analyzed. This tendency, which sets fullerenes apart from other large molecules, underlies many aspects of fullerene behavior in solutions, such as the recently discovered nonmonotone temperature dependence of fullerene solubility in various solvents, the nonlinear concentration dependence of nonlinear optical susceptibility, the sharp dependence of the color of a fullerene solution on the solution composition (the solvatochromatic effect), the concentration dependence of the heat of solution of fullerenes in organic solvents, etc. Growth mechanisms of fractal clusters in fullerene solutions are analyzed along with similarity laws determining the thermodynamic characteristics of fullerite crystals.

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The diffusion of fullerenes in solution is studied taking into account the recently established formation of clusters containing numbers of aggregated fullerence molecules. Based on a droplet model of a cluster, the distribution function of fullerence clusters by size is obtained for various concentrations of solution. It is shown that dissolved fullerene is present mainly in the form of clusters at saturation conditions, but the contribution of clusters diminishes as the concentration decreases. Since the diffusion mobility of clusters is much less than that of molecules, it leads to the dependence of an effective diffusion coefficient on concentration, which is computed for the case of fullerence C60. The feasibility of the use of this dependence as a basis for a diffusion method of the separation and enrichment of the fullerene extract with a small addition of higher fullerenes is analyzed. Possible schemes for enrichment are discussed.

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