Aggregation of Fullerene, C₆₀, in Benzonitrile

Abstract

C60 solutions in benzonitrile have been found to show concentration dependent optical absorption behaviour. At lower concentrations (<100 μM) the UV−vis absorption characteristics of C60 in benzonitrile are exactly similar to those in benzene and decalin. At higher concentrations (>100 μM), however, the C60 solutions in benzonitrile show very broad absorption tail, extending beyond 900 nm. At higher concentrations the solutions are also visually opaque. From picosecond laser flash photolysis experiments it is seen that the triplet quantum yield of C60 in benzonitrile at higher concentrations (∼400 μM) is much less than unity and increases with the dilution while in decalin and benzene it is always close to unity and independent of the C60 concentration. Dynamic light scattering experiments indicate the presence of particles of mean size of about 250 nm in C60 solutions in benzonitrile with concentration >100 μM, while in <100 μM solutions no such particles have been observed. Such particles are also not observed for C60 solutions in benzene and decalin, even up to ∼500 μM. Scanning electron microscopy also shows particles of size ∼250 nm. It is inferred that C60 forms aggregates in benzonitrile at concentrations >100 μM and that the aggregated and the monomeric form of C60 are in equilibrium.