Radiation chemical and photophysical properties of C60(C4H8SO3Na)n in aqueous solution:: A laser flash photolysis and pulse radiolysis study

Optical absorption studies on aqueous solutions of C-60(C4H8SO3Na)(n) (n = 4-6) revealed deviation from the Beer-Lambert law in the 250-350 nm region, which is assigned to the formation of solute aggregates at concentrations higher than 1 x 10(-3) mol dm(-3). Dynamic light scattering experiments showed aggregates with an average size of similar to 100 nm. The solute has a broad weak fluorescence emission (phi (f) = 1.8 x 10(-3)) in the 450-650 nm region, which remained independent of solute concentration. The broad transient absorption band in the 450-900 nm region (epsilon (660) = 2170 dm(3) mol(-1) cm(-1)), which formed immediately on laser flash photolysis (lambda (ex) = 355 nm, 35 ps), is assigned to singlet-singlet transition. It decays to a tripler excited state whose absorption is observed to depend strongly on salute concentration. In dilute solutions, an absorption band with lambda (max) = 590 nm is seen, and at high solute concentration a broad absorption in the 500-900 nm region is observed. The e(aq)(-) reacts with the solute with a bimolecular rate constant of 1.7 x 10(8) dm(3) mol(-1) s(-1) and forms weak broad absorption bands at 440, 540, 670, 870, 940, and 1020 nm. Isopropanol radicals also react with the solute with a bimolecular rate constant of 2.3 x 10(8) dm(3) mol(-1) s(-1) with the formation of a transient optical absorption spectrum similar to that observed on reaction with e(aq)(-) and assigned to a solute radical anion. Thr H-. and (OH)-O-. radicals react with bimolecular rate constants of 3.2 x 10(9) and 4.4 x 109 dm(3) mol(-1) s(-1), respectively, and form transient absorption bands at 440, 510, and 660 nm. Based on electron transfer studies with suitable electron donor/acceptor substrates, the ranges of the reduction and oxidation potentials of the solute an estimated.