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

Free standing polypyrrole (PPY) films, electrochemically prepared with diff erent types of electrolytes (sodium toluenesulfonate (NaTSO), p-toluenesulf onic acid (ATSO) and lithium perchlorate (LiClO4)) were investigated by two different spectroscopic methods. Specular reflectance measurements were pe rformed by Fourier transform infrared (FTIR) spectroscopy in the range 200- 6000 cm(-1). The optical constants for PPY films were calculated from the r eflectance spectra with Kramers-Kronig technique. The reflection spectra ar e sensitive to the nature of the electrolyte and to the d.c. conductivity v alues. The absorption spectra of PPY films were obtained in the range 2500- 25 000 cm(-1) by photopyroelectric (PPE) spectroscopy. Besides the bipolaro nic absorption bands, this method reveals the characteristic vibrational ba nds of NH and N+H. The observed changes of the intensity of these bands aft er the electrochemical reduction and subsequent treatment with HCl are due to the deprotonation and protonation processes in the PPY samples. (C) 1999 Elsevier Science S.A. All rights reserved.