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 µ M) the UV-vis absorption characteristics of C₆₀ in benzonitrile are exactly similar to those in benzene and decalin. At higher concentrations (>100 µ M), 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 µ M) 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 µ M, while in <100 µ M solutions no such particles have been observed. Such particles are also not observed for C₆₀ solutions in benzene and decalin, even up to ~500 µ M. Scanning electron microscopy also shows particles of size ~250 nm. It is inferred that C₆₀ forms aggregates in benzonitrile at concentrations >100 µ M and that the aggregated and the monomeric form of C₆₀ are in equilibrium.