A new and robust method for In-situ EPR electrochemistry

Electron paramagnetic resonance (EPR) is a powerful technique for the study of systems with paramagnetic centers and is among the most important tools for studying transient radical-pairs in photoexcited systems. In these experiments EPR signals of the transient charge separated states, of D^●+A^●-, are observed.

This increase in understanding redox processes and various complex reactions associated with paramagnetic intermediates has been strongly promoted by the application of in-situ spectroelectrochemical techniques. Due to its high sensitivity towards paramagnetic species, EPR can provide key information about radical species generated or consumed during electrode reaction. Thus, EPR complement electrochemical data from other techniques by directly identifying radical species, confirming reaction mechanisms and revealing more subtle. EPR spectroscopist have also found that in-situ electrochemical EPR is a feasible option to standard optical study of electrochemistry.

Currently, most studies of the paramagnetic intermediates in electron transfer reactions are performed by generating them chemically ex-situ, followed by a transfer to the spectroscopic cell. In most cases those paramagnetic intermediates are not long lived and need an oxygen free environment, in addition chemical generation of these radical ion intermediates is not as accurate as electrochemical one and can generate by-products as well. This process is complex; therefore, we present a new and simple design of electrochemical setup for in-situ generation of free radicals to be measured using X-band. The cell parts are all from commercially available components and requires no specially made glassware. The EPR performance of the setup is demonstrated by in-situ electrochemical generation of organic radicals such as quinones, perylene-diimide, pyrene, flavin, tryptophan and tyrosine through oxidation or reduction in solution. The well-resolved EPR spectra of the radical products were simulated and analyzed and the hyperfine coupling constants have been assigned for the interactions of the unpaired electron with its` environment.