in situ ESR-UV/Vis EC
In situ ESR-UV-Vis-NIR-spectroelectrochemistry
The assignment of peaks in electronic absorption spectra to paramagnetic species by simultaneous measurement of ESR and UV-Vis-NIR spectra is only possible in an unambiguous way if there is no interference with the absorptions of other products.
In most of the practical cases there are strong interferences, especially in the case of conducting polymers.
The simultaneous measurement of the concentration of paramagnetic species, injected electric charge and electronic absorption spectra allows the calculation of the pure single spectra by linear regression. The following spectra will demonstrate the brilliant ability of this method.
These spectra were taken from a polyaniline layer during a potential sweep from -50 mV to 350 mV and back to -50 mV. Absorptions of the starting material and the formed products during electrochemical oxidation and re-reduction are superimposed. An unambiguous assignment of polaron and polaron/dimer absorption is impossible.
Pure UV-Vis-NIR-spectra of the formed polaron during electrochemical doping of polyaniline obtained by separation.
Pure UV-Vis-NIR-spectra of the spinless double charged species formed during electrochemical oxidation and re-reduction of polyaniline. There is clear evidence that there is no capacitive current.
Furthermore, the measurement of the number of spins formed and comparison with the charge flown allows to decide whether the measured radicals by ESR-spectroscopy are primary radicals or radicals which were formed in an equilibrium or follow up reaction.