Matrix rank analysis of spectral studies on the electropolymerisation and discharge process of conducting polypyrrole/dodecyl sulfate films

The polymerisation of pyrrole in aqueous sodium dodecyl sulfate (SDS) solution was studied systematically by in situ spectroelectrochemical technique including the optical changes during the reduction of the freshly prepared film. In order to determine the number of species formed during the anodic oxidation, the spectra registered during the deposition and the electrochemical reduction were evaluated by matrix rank analysis (MRA). This treatment of the data led to the conclusion that the spectral changes can be interpreted only by assuming five independent absorbing species, which could be uniformly detected during both the regular and irregular reduction reported in our recent work. The results were completed by a study on the pH and SDS concentration dependence of the solution phase oligomerisation during the chemical 'aging' of the monomer solution, which leads to a product absorbing also in the visible range. On the basis of the observations, the two extra species found beyond the neutral, monocationic and dicationic species were identified as a protonated neutral segment and its oxidized form.