An intermediate state of the triphenylamine cation radical revealed using an electron-transfer stopped-flow method

Using an electron-transfer stopped-now method, the triphenylamine cation radical (TPA(.+)) was generated in acetonitrile via the electron transfer between TPA and the tris(p-bromophenyl)amine cation radical (TBPA(.+)), and the changes in the absorption spectra were observed. The well-known decay process of TPA(.+) was observed in the absence of TPA, reflecting the dimerization reaction of TPA(.+) and the consecutive electron-transfer reactions of the dimer compound, tetraphenylbenzidine (TPB). When TBPA(.+) was mixed with a large excess amount of TPA, new absorption peaks appeared around 400 and 850 nm. No time changes were observed for these peaks, while the decrease in TPA(.+) and the increase in TPB.+ were observed overlapping on these peaks. The new absorption spectrum can he assigned to that of (TPA)(2)(.+), or, more presumably, (TPA)(n)(.+) Although (TPA)(n)(.+) has not been recognized as an intermediate in the electrochemical oxidation of TPA. it has been ascertained that (TPA)(n)(.+) is electrochemically generated under certain conditions, e.g., during the initial stage of the oxidation of TPA in a stirred solution containing a sufficient amount of TPA. (C) 2001 The Electrochemical Society.