ИСТИНА

Raman spectroelectrochemistry is a powerful tool to monitor structural transformations during electrosynthesis and doping/dedoping of conducting polymers. However, the excitation laser beam passes several interfaces, where absorption, refraction and reflection processes may occur. These are: air/glass (the wall of spectroelectrochemical cell); glass/electrolyte; electrolyte/film (of conducting polymer); film/electrode. Noteworthy, the film of conducting polymer changes its thickness, absorption and refraction during the electrosynthesis and doping/dedoping. Moreover, conducing polymer films are inhomogeneous consisting of conductive domains distributed in non-conductive matrix, these domains changing their sizes during doping/dedoping. All these phenomena, as well as the electrode material, laser excitation wavelength and Raman resonance phenomena due to specific absorption of laser radiation, influence the shape of in situ Raman spectra and are also dependent on the incident angle of the laser beam. These issues are illustrated on the example of electrosynthesis and redox transformations of thin (<150 nm) films of polyaniline (PANI) and poly(3,4- ethylenedioxythiophene) (PEDOT). Fiber optics Raman spectrometer with 180􀁱 (back) scattering geometry, 532 nm laser excitation, Pt sheet and standard 2 cm quartz spectrophotomeric cell were used. It was shown that Pt electrode immersed into deionized water exhibits an intense Raman signal near 600 and 1650 cm-1, as well as some other bands in the most informative Raman range of 600-1650 cm-1 (Fig. 1a). Similar vibrations can be found in the spectrum of Pt coated by reduced PANI film (-0.2V vs. Ag/AgCl), which is most transparent to 532 nm radiation (Fig. 1b). By increasing incident angle of the laser beam from 0 (perpendicular) to 8-11 degrees one can minimize the intensity of 600 and 1645 cm-1 vibrations in the spectra of both bare Pt and reduced PANI film thus minimizing the influence of multiple interfaces on the spectrum shape. This is less evident for PEDOT films absorbing 532 nm radiation in all oxidation states.