EXCITED-STATES AND ELECTRON-TRANSFER REACTIONS OF C-60(OH)(18) IN AQUEOUS-SOLUTION

Dynamic light scattering of fullerenol solutions [C-60(OH)(18)] reveal s evidence for the formation of fullerene aggregates at high solute co ncentration (up to 3.85 x 10(-2) mol dm(-3)). This hydrophilic fullere ne derivative emits very weak fluorescence regardless of its concentra tion. Photolysis (35 ps; lambda(ex) = 355 nm) of C-60(OH)(18) in aqueo us solution yields the immediate formation of a transient singlet exci ted state with broad absorption in the 550-800 nm region with epsilon( 670nm) = 2130 dm(3) mol(-1) cm(-1). The energetically higher-lying sin glet excited state transforms via intersystem crossing (i.e., with tau (1/2) = 500 ps) to the also broadly absorbing (550-800 nm), triplet ex cited state. In contrast, at low solute concentration, the features of the (T-1 --> *T-n) absorption differ significantly exhibiting an abs orption maximum at 650 nm concomitant to a shoulder at 570 nm. The pi- radical anion of fullerenol, [C-60(OH)(18)](.-), generated by electron transfer from hydrated electrons and (CH3)(2)C-.(OH) radicals, absorb s with lambda(max) at 870, 980 and 1050 nm. Based on electron transfer studies with suitable electron donor/acceptor substrates, the reducti on potential of the C-60(OH)(18)/[C-60(OH)(18)](.-) couple was estimat ed to be in the range between -0.358 and -0.465 V vs. NHE.