Abstract
The Stern-Volmer plot of fluorescence quenching of pyrene by C <sub>60</sub> (or C <sub>70</sub> ) is upward, and non linearly proportional to the fullerene concentration. Electronic absorption measurements show that pyrene and C <sub>60</sub> do not form static complexes under the experimental condition. A novel 'inner filter effect' model is proposed to rationalize the observed non linear upward Stern Volmer behavior. At a given C <sub>60</sub> concentration, increasing either solvent polarity or temperature (T>280 K) causes diminishment in the I <sub>0</sub> /I ratio. The data strongly suggest that even at concentrations far below saturation, fullerenes form aggregates in organic solvents.