Differential Photoactivity of Aqueous [C_(60)] and [C_(70)] Fullerene Aggregates

摘要

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 hecause 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 ~1O_2 generation, including the measurement of ~1O_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.