Spectroscopic Studies of Fullerene Aggregates

Abstract

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 photoluminescence spectroscopy. Solute aggregation exhibiting reaction-limited kinetics was observed to occur over a period of several days in ∼1 mM C 60 solutions in benzene. Aggregation was irreversible and could be suppressed by addition of a soluble radical scavenger, suggesting a radical mechanism for aggregate formation. Dynamic light scattering measurements determined that the aggregates attain a hydrodynamic radius of ∼300 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, radius of gyration, and fractal dimension of the aggregates. Photoluminescence spectra of aggregates were compared with those of the crystalline materials. The luminescence spectra of solutions containing aggregates were found to differ substantially from the luminescence spectra of unassociated fullerene. The chief effect of aggregate formation is the appearance of excimer-like features in the photoluminescence spectrum.