Photochemical and Photophysical Properties of Sequentially Functionalized Fullerenes in the Aqueous Phase

Abstract

The vast range of C-60 derivatives makes it difficult to assess the potential environmental impact of this class of materials, while past environmental studies mostly focused only on pristine C-60. Central to derivatized C-60's potential to negatively impact (micro)biological receptors upon unintended release is its unique property of mediating the transfer of light energy to ambient oxygen, producing O-1(2). To initiate the process of establishing a thorough understanding of the photoinduced adverse biological effects of functionalized fullerenes and their aqueous dispersions, the photochemical properties relevant to O-1(2) production were evaluated using three selected series of mono-, bis-, and tris-adducted fullerene materials. Differential O-1(2) production of derivatives in toluene were explained by spectral variations under visible and UVA light conditions. Of the nine functionalities studied only aggregates of two positively charged derivatives showed significant photoactivity under experimental conditions. Laser flash photolysis revealed a triplet excited state in the photoactive aggregates with a sufficiently long lifetime to be quenched by O-3(2). Dynamic light scattering, transmission electron microscopy, and electron diffraction patterns revealed aggregates with sizes typical of aqueous C-60 colloids that varied in crystallinity based on functionality. Results raised questions about our current understanding of the photoactivity of fullerene aggregates.