Resonance Raman measurement of electrochemically generated short-lived intermediates by means of a pulse electrolysis stopped flow method

Abstract

Resonance Raman (RR) measurement with a pulse electrolysis stopped flow method was developed for the purpose of the measurement of electrochemically generated short-lived intermediates. In this method the solution, electrolysed by imposing a current pulse on a column electrode, is delivered to an optical flow cell by means of a stopped flow technique and then the RR spectrum is observed at the optical cell. The RR spectrum of the triphenylamine cation radical (TPA .+), which dimerizes rapidly to produce the dimeric compound tetraphenylbenzidine (TPB), was successfully measured selectively without any interference by the oxidation products of TPB generated in subsequent electron transfer reactions. The RR spectrum of TPA .+ obtained had a different profile from that of the dimer cation radical (TPB .+) but was quite similar to that of the dimer dication (TPB 2+). This result shows the similarity between the vibrational structures of TPA .+ and TPB 2+, which can be explained by their canonical structures. By using the proposed method, it should become possible to observe the RR spectra of electrogenerated intermediates whose half-lives are several tens of milliseconds.