In situ spectroelectrochemistry of 2,5-diphenyl-1,3,4-oxadiazole

The electrochemical reduction of 2,5-diphenyl-1,3,4-oxadiazole has been studied by both cyclic voltammetry and spectroelectrochemistry. The in situ spectroscopic techniques were applied to obtain structural information on the products of the follow-up reactions. Time-resolved UV-vis spectroscopy, with spectra measured on a time scale of 20 ms by a diode array spectrometer, was used in cyclic voltammetry to obtain up to 60 single spectra in the forward and backward scans. The radical anion of 2,5-diphenyl-1,3,4-oxadiazole, which is formed in the electron transfer reaction at the electrode, was studied by ESR spectroscopy. Furthermore, paramagnetic products of the follow-up reactions were detected. A reaction mechanism is formulated that includes an irreversible protonation reaction and, in parallel, a reversible ion-pairing reaction with the supporting electrolyte cation for the electrochemically generated radical anion and an irreversible follow-up reaction for the dianion of 2,5-diphenyl-1,3,4-oxadiazole.