Spectroscopic studies of fullerene aggregates

The growth and structure of fullerene (C-60 and C-70) aggregates in single and binary mixed-solvent solutions were examined by light scattering and ph otoluminescence spectroscopy. Solute aggregation exhibiting reaction-limite d kinetics was observed to occur over a period of several days in similar t o 1 mM C-60 solutions in benzene. Aggregation was irreversible and could be suppressed by addition of a soluble radical scavenger, suggesting a radica l mechanism for aggregate formation. Dynamic light scattering measurements determined that the aggregates attain a hydrodynamic radius of similar to 3 00 nm before sedimentation occurs. Solutions containing stable suspensions of fullerene aggregates were also prepared by addition of a poor solvent to a solution of fullerene in a strong solvent. Both static and dynamic light scattering methods were used to determine the mass, hydrodynamic radius, r adius of gyration, and fractal dimension of the aggregates. Photoluminescen ce I spectra of aggregates were compared with those of the crystalline mate rials. The luminescence spectra of solutions containing aggregates were fou nd to differ substantially from the luminescence spectra of unassociated fu llerene. The chief effect of aggregate formation is the appearance of excim er-like features in the photoluminescence spectrum.