Temperature dependence of the nonexponential decay of photoproduced N,N,N′,N′-tetramethylbenzidine cation radicals in sodium dodecylsulfate micelles: Determination of activation energy distributions and relation to dynamic cooperativity

Abstract

The temperature dependence of the decay of photoproduced N,N,N′,N′-tetramethylbenzidine cation radicals (TMB+) in sodium dodecylsulfate (SDS) micellar solutions was studied with and without added sodium chloride. The distributions of activation energies g(E) associated with the lifetime distributions f(τ) for the cation radical decay were determined. The f(τ) distributions over a range of 287 to 328 K were determined from the inverse Laplace transform of the radical cation decay curves described by [TMB]/[TMB]0=exp[−t/τ0)α]. The g(E) distributions show a maximum at about 1.5 of the theoretical potential energy maximum for single bond rotation in isolated hydrocarbon chains which is consistent with values estimated for constrained environments. This supports the importance of cooperativity as the origin of time dependent decay of embedded species in constrained environments such as micelles.