Effect of solvent polarity on the aggregation of fullerenes: a comparison between C60 and C70

Effect of solvent polarity on the aggregation behaviour of C70 has been investigated in several mixed solvents using optical absorption, fluorescence, dynamic light scattering and scanning electron microscopic measurements and compared with those observed for the other fullerene analogue, C60. It is seen that similar to C60, aggregation of C70 also requires the solvent polarity to exceed some critical value. In terms of solvent dielectric constant the critical solvent polarity, required for C70 aggregation is found to be in the range of ∼27–31, which is much higher than that required for C60 aggregation (∼12–14). The large difference in the critical solvent polarity required for C60 and C70 aggregation has been rationalized on the basis of the molecular shapes and the polarizabilities of two fullerene molecules.