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

Effect of solvent polarity on the aggregation behaviour of C-70 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, C-60. It is seen that similar to C-60, aggregation of C-70 also requires the solvent polarity to exceed some critical value. In terms of solvent dielectric constant the critical solvent polarity, required for C-70 aggregation is found to be in the range of similar to27-31, which is much higher than that required for C-60 aggregation (similar to12-14). The large difference in the critical solvent polarity required for C-60 and C-70 aggregation has been rationalized on the basis of the molecular shapes and the polarizabilities of two fullerene molecules. (C) 2002 Elsevier Science B.V. All rights reserved.