RADIATION CHEMICAL AND PHOTOPHYSICAL PROPERTIES OF C60(C4H8SO3Na) n IN AQUEOUS SOLUTION: A LASER FLASH PHOTOLYSIS AND PULSE RADIOLYSIS STUDY

Abstract

Optical absorption studies on aqueous solutions of C60(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 × 10−3 mol dm−3. Dynamic light scattering experiments showed aggregates with an average size of ∼100 nm. The solute has a broad weak fluorescence emission (ϕf = 1.8 × 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 (ϵ660 = 2170 dm3 mol−1 cm−1), which formed immediately on laser flash photolysis (λex = 355 nm, 35 ps), is assigned to singlet-singlet transition. It decays to a triplet excited state whose absorption is observed to depend strongly on solute concentration. In dilute solutions, an absorption band with λmax = 590 nm is seen, and at high solute concentration a broad absorption in the 500–900 nm region is observed. The eaq − reacts with the solute with a bimolecular rate constant of 1.7 × 108 dm3 mol−1 s−1 and forms weak broad absorption bands at 440, 540, 620, 870, 940, and 1020 nm. Isopropanol radicals also react with the solute with a bimolecular rate constant of 2.3 × 108 dm3 mol−1 s−1 with the formation of a transient optical absorption spectrum similar to that observed on reaction with eaq − and assigned to a solute radical anion. The •H and −OH radicals react with bimolecular rate constants of 3.2 × 109 and 4.4 × 109 dm3 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.