Differential Photoactivity of Aqueous [C60] and [C70] Fullerene Aggregates

Many past studies have focused on the aqueous photochemical properties of colloidal suspensions of C-60 and various [C-60] fullerene derivatives, yet few have investigated the photochemistry of other larger cage fullerene species (e.g., C-70, C-74, C-84, etc.) in water. This is a critical knowledge gap because these larger fullerenes may exhibit different properties compared to C-60, including increased visible light absorption, altered energy level structures, and variable cage geometries, which may greatly affect aggregate properties and resulting aqueous photoactivity. Herein, we take the first steps toward a detailed investigation of the aqueous photochemistry of larger cage fullerene species, by focusing on [C-70] fullerene. We find that aqueous suspensions of C-60 and C-70, nC(60) and nC(70), respectively, exhibit many similar physicochemical properties, yet nC(70) appears to be significantly more photoactive than nC(60). Studies are conducted to elucidate the mechanism behind nC(70)'s superior O-1(2) generation, including the measurement of O-1(2) production as a function of incident excitation wavelength, analysis of X-ray diffraction data to determine crystal packing arrangements, and the excited state dynamics of aggregate fullerene species via transient absorption spectroscopy.