Electrochemical and optical characteristics of the hole conducting material N,N '-diphenylbenzidine during oxidation in DMF

The electrochemical oxidation of the hole conducting material N, N'-dipheny lbenzidine (DPB) in N,N-dimethylformamide (DMF) was investigated by cyclic voltammetry and spectroelectrochemistry. The results were compared to elect ro-oxidation in acetonitrile. Time-resolved UV-Vis spectroscopy, with spect ra measured on a time scale of 20 ms by a diode array spectrometer, was use d in conjunction with cyclic voltammetry to monitor the progress of electro chemical oxidation and reduction in situ and to obtain kinetic and structur al information on reaction products. The oxidation of DPB in DMF is quasi-r eversible at E-sw < + 1.2 V (vs. Ag/AgCl), while at higher switching potent ials, the oxidation is followed by chemical reactions leading to the polyme rization of DPB. The radical cation DPB+; which can be transformed into the neutral radical DPB. through the loss of a proton, was detected in the oxi dation by in situ ESR spectroscopy. A reaction mechanism was proposed for t he oxidation processes. Structural changes induced in DPB at high potential s are suspected to be accountable for device failure of DPB based light-emi tting diodes (LEDs) in applications. (C) 1999 Elsevier Science S.A. All rig hts reserved.