Unexpected Disparity in Photoinduced Reactions of C and C in Water with the Generation of O or O.

Well-defined fullerene-PEG conjugates, C-PEG () and two C-PEG ( and with the addition sites on [6,6] and [6,6]-junctions), were prepared from their corresponding Prato monoadduct precursors. The resulting highly water-soluble fullerene-PEG conjugates - were evaluated for their DNA-cleaving activities and reactive oxygen species (ROS) generation under visible light irradiation. Unexpectedly, photoinduced cleavage of DNA by C-PEG was much higher than that by C-PEG and with higher absorption intensity, especially in the presence of an electron donor (NADH). The preference of photoinduced ROS generation from fullerene-PEG conjugates - via the (energy transfer) or the (electron transfer) photoreaction was found to be dependent on the fullerene core (between C and C) and functionalization pattern of C (between and ). This was clearly supported by the electron transfer rate obtained from cyclic voltammetry data and computationally estimated relative rate of each step of the and the reactions, with the finding that energy transfer reactions occurred in the inverted Marcus regime while electron transfer reactions proceeded in the normal Marcus regime. This finding on the disparity in the pathways of photoinduced reactions ( versus ) provides insights into the behavior of photosensitizers in water and the design of photodynamic therapy drugs.