Raman and resonance-Raman spectra of polypyrrole with application to sensor - gas probe interactions

Raman spectra of the oxidized and neutral forms of polypyrrole show a relative intensity shift from the high wave number region to the low wave number region as the source wavelength is increased from 514.5 to 1064 nm. Variations in band positions are also observed with changes in excitation source; particularly, two C=C stretches at 1500 and 1605 cm −1 can be observed with the neutral polymer but only a single band is observed at 1575 cm −1 when sources of higher energy are used. These changes arise from differences in the electronic states of the two forms that can greatly alter the intensities of the numerous bands. The oxidized and neutral forms of the polymer both act as electron acceptors towards the gas phase species tested here (toluene, water, methanol, and ammonia). The increased electron density induces an upward shift of the peaks at 915 and 1035 cm −1 of the neutral polymer and increases the relative intensity of the 1575 cm −1 peak of the oxidized polymer using 1064 and 514.5 nm sources, respectively. Keywords: polypyrrole, Raman spectroscopy, gas probe interactions.