Optical studies on free-standing polypyrrole films by the photopyroelectric method

Optical spectra of free-standing polypyrrole films were investigated by a novel PhotoPyroElectric (PPE) method. The reflection and absorption spectra in the range 2000–25000 cm^–1 of TsO^–- and ClO ₄ ^su– -doped polypyrrole films were obtained with an experimental setup comprising two pyroelectric sensors. The absorption bands due to electronic transitions to the bonding and antibonding bipolaronic levels appear at 11 000 and 21 500 cm^–1, respectively. Some relevant details in the polypyrrole spectrum in the 2000–5000 cm^–1 range were observed. The absorption band located at 3400 cm^–1 is characteristic for NH stretching vibration. The bands in the 2300–2500 cm^–1 range are ascribed to the vibration of N⁺H groups containing positively charged nitrogen. The PPE spectra also reveal changes of the electronic and vibrational absorption bands after polymer reduction and HCl treatment.