Studies of the photoexcited states of the fullerenes, C60 and C70

The spectra of C60 and C70 were examined using low-temperature photoluminescence and quasi-elastic light scattering spectroscopy. A detailed vibronic analysis of the lowest triplet and singlet excited states of C70 is obtained. The lowest triplet state is identified as a 3E1′ state and the vibronic structure consists primarily of Herzberg-Teller active e2′ modes. The intensity of the electronic origin is comparable to the vibronically induced intensity and is extraordinarily solvent sensitive. The spectrum of monosubstituted C60 is shown to be qualitatively similar to that of C60 in polar or strongly complexing solvents. The principal effect of solvent interaction or substitution is to induce dipole intensity in the orbitally forbidden electronic origins of the luminescent states of C60 and C70. The Rayleigh scattering of fullerene solutions illustrates that solute aggregation occurs easily and that aggregate nucleation is strongly affected by surfaces in contact with the solution.