Reflection and absorption studies on polypyrrole films electrochemically prepared with different electrolyte types

Free standing polypyrrole (PPY) films, electrochemically prepared with different types of electrolytes (sodium toluenesulfonate (NaTSO), p-toluenesulfonic acid (ATSO) and lithium perchlorate (LiClO4)) were investigated by two different spectroscopic methods. Specular reflectance measurements were performed by Fourier transform infrared (FTIR) spectroscopy in the range 200–6000 cm−1. The optical constants for PPY films were calculated from the reflectance spectra with Kramers–Kronig technique. The reflection spectra are sensitive to the nature of the electrolyte and to the d.c. conductivity values. The absorption spectra of PPY films were obtained in the range 2500–25 000 cm−1 by photopyroelectric (PPE) spectroscopy. Besides the bipolaronic absorption bands, this method reveals the characteristic vibrational bands of NH and N+H. The observed changes of the intensity of these bands after the electrochemical reduction and subsequent treatment with HCl are due to the deprotonation and protonation processes in the PPY samples.