Raman spectroelectrochemical study of polyaniline at UV, blue, and green laser line excitation in solutions of different pH

A detailed study on Raman spectroelectrochemistry of polyaniline layer deposited at a gold electrode was performed. Raman spectra were excited by three laser wavelengths: UV line at 325 nm, a blue line at 442 nm, and a green line at 532 nm in solutions of different pH ranging from 1 to 9, and at different electrode potentials ranging from −0.5 V to 0.8 V. UV excitation results in a strong resonance with the reduced leucoemeraldine form of polyaniline that absorbs visible light at a maximum around 315 nm, revealing features characteristic for this form, thus nearly avoiding the possibility to observe the oxidised form and the corresponding electrochemical redox transformations. Both redox forms and their redox interconversions depending on electrode potential and solution acidity were well observed and analysed for green laser line excited Raman spectra. Blue laser line probably appears in resonance with the intermediate polyaniline form that absorbs visible light at a maximum of 420 nm.