Substituent Effects on the Electrochemical Properties of Pyrroles and Small Oligopyrroles

The electrochemical oxidation of several oligopyrroles, either unprotected, partially blocked, or totally blocked on their α-terminal positions or N-substituted, has been investigated in acetonitrile by cyclic voltammetry. For all the studied oligopyrroles, reversible voltammograms have been obtained at moderate to high scan rates, whereas chemical evolutions of the cation radicals have been observed at lower scan rates. The one-electron redox potentials, E °, of the oligopyrrole/oligopyrrole cation-radical couples have been measured and the lifetimes of the cation radicals have been estimated. The stabilities of the cation radicals have been examined as a function of the chain length and the nature of the substituent.