Electron transfer to buckminster-fullerenes and functionalized fullerene derivatives in aqueous and protic media, as studied by radiolytic techniques

The primary radical products, namely C-60(.-) and C-70(.-) which were formed by reactions with either the solvated electrons or (CH3)(2)C-.(OH) radicals exhibit distinct absorption bands in the near-IR. Reaction of a water-soluble C-60/gamma-cyclodextrin complex with alpha-hydroxyalkyl radicals and hydrated electrons also involves electron transfer, as indicated by the dependence of the rate constants on the redox potential of the reducing species. Pulse radiolysis of micellar C-60 solutions in BRIJ 35 and Triton X-100, on the other, exhibited electron transfer from various reducing radicals to the fullerene core. Water soluble fullerene mono-derivatives, e.g. C-60[C(COO-)(2)](2) (1) and C-60(C9H11O2)(COO-) (2) did not show any noticeable reactivity towards strongly reducing species which can be ascribed to the formation of clusters in which the hydrophobic fullerene core is shielded by a surrounding layer of negatively charged carboxylate functions. Upon incorporation into gamma-cyclodextrin the reduction of 1 and 2 occurs rapidly as indicated by both an accelerated decay of the hydrated electron absorption and the formation of the characteristic near-IR absorption due to (C-60(.-))[C(COO-)(2)]/gamma-CD and (C-60(.-))(C9H11O2)(COO-/gamma-CD at 1030 nm. The all-equatorial bis- and tris-adducts, e.g. equatorial-C-60[C(COO-)(2)](2) and equatorial-C-60[C(COO-)(2)](3), did not show any evidence with respect to the occurrence of aggregation phenomena and yielded the respective radical anions equatorial-(C-60(.-))[C(COO-)(2)](n) in high yields.