Study of multicenter redox molecules with square wave voltammetry

An analytical explicit expression for the current obtained with the well-known multipulse technique square wave voltammetry (SWV), corresponding to the reversible reduction/oxidation of multicenter redox molecules whose centers may or may not interact, has been given in Appendix. This equation is valid for spherical electrodes of any size, including planar electrodes (r(0) -> infinity) and ultramicroelectrodes (r(0) -> 0) as limit cases, and it also permits us to deduce the behavior of these processes at the limit situations corresponding to small and great square wave amplitudes. For the sake of simplicity, we have analyzed the behavior of bicenter molecules, ranging from noninteracting centers, for which the square wave current obtained is twice that corresponding to a single E mechanism, to strongly interacting centers which present two successive and well-separated signals of one electron each. The results obtained here are easily extendable to molecules with any number of redox centers. The theoretical predictions have been tested with two experimental systems, quinizarine in acetonitrile and pyrazine in aqueous acid media, and an excellent agreement between theory and experiments is found.