Voltammetric studies of photochemically generated free radicals

Steady-state currents for oxidation and reduction of photochemically generated radicals have been detected using platinum microelectrodes. Diphenylmethyl radicals were produced by photolysis of sym -tetraphenylacetone or photolysis of a mixture of tert-butyl peroxide and diphenylmethane. Equations were derived that relate the steady-state currents to the concentration of radicals far from the electrode, the diffusion coefficient and the rate constant for disappearance of the radicals. It was shown that about 2 μM of diphenylmethyl radicals was being produced under the experimental conditions. The oxidation of diphenylmethyl radicals could also be detected by normal pulse voltammetry at 25 μm diameter microelectrodes. Reverse pulse voltammetry at 1 ms measurement times revealed the reduction current for diphenylmethyl cations in acetonitrile and in methylene chloride. The reversible carbenium ion/neutral radical potential was 0.00 ± 0.01 V vs. ferricinium/ferrocene in acetonitrile. Similarly, the reversible potential for the diphenylcyanomethyl radical/carbanion couple was − 0.96 V vs. ferrocene.