in situ IR
In situ FTIR spectroelectrochemistry
In situ FTIR (Fourier Transform Infrared) spectroelectrochemistry is a powerful technique to study conducting polymers. As an example, the structure and stabilization of charged states during p-doping of polyaniline can be followed here. The infrared spectra of polyaniline in their conductive (doped) states are characterized by the appearance of very intense infrared vibration bands. These bands generally appear in the range between 1600 and 700 cm−1, and they are related to the conductivity of polyaniline. They provide not only structural but also electronic information. Usually they are accompanied by broad IR absorption bands (around 1500–5000 cm−1) related to the formation of free charge carriers during charging the polymer film. Doping induced modes at 1572, 1476, 1318 1250, and 1145 cm-1 indicate the presence of delocalized charge carriers (polaron) in the polymer structure. These bands increase from -0.1 V up to 0.3 V and pass over to a constant value. By the back scan these five peaks reach their maximum at 0 V. At the same time, at 0.3 V two new peaks appear at 1626 and 1375 cm-1 increasing exponentially by the potential forward scan. These bands are can assigned to quinoidic structures (bipolaron) in polyaniline. During the back scan the intensity of these peaks decrease and they disappear at 0 V. By dedoping the bipolarons are completely transformed into polarons, as seen by the disappearance of the characteristic bands.
In situ FTIR spectra measured during the anodic oxidation of polyaniline
Potential dependence of the normalized absorbance of selected bands during oxidation of polyaniline.