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.