Red and NIR laser line excited Raman spectroscopy of polyaniline in electrochemical system.

Highlights • Raman spectra obtained at 532, 633, and 785 nm excitations show different dependencies on electrochemical variables. • Intensities of selected Raman bands correlate with absorption spectra of different redox forms of polyaniline. • The shift of the onset potential for Raman bands intensity growth to less positive values proceeds by increasing of solution pH. Abstract Polyaniline has been electrodeposited at a gold electrode, and subjected to Raman spectroelectrochemical study at a red (633 nm) and NIR (785 nm) laser line excitations at electrode potentials varying from −0.5 V to 0.8 V, and different solution pH values ranging from 1 to 9. The results obtained are compared with 532 nm excitation spectra. Some new phenomena have been observed and discussed. The 1620 cm−1 Raman band diminishes in its intensity with a positive potential shift at a green excitation, whereas a maximum of intensity for this band around 0.6 V was observed for the red excitation. Adversely, a positive potential shift causes an increase of intensity for 1585 cm−1 band for both these excitation wavelengths. For NIR excitation, both these bands grow in intensity by positive potential shift. This behavior, as well as increase of spectral intensity with a progressive oxidation of polyaniline layer, were interpreted based on the differences of optical absorption and its changes with changing electrode potential. For the most Raman bands, the shift of the onset potential for their intensity growth to less positive values has been observed by increasing of solution pH. [ABSTRACT FROM AUTHOR]