Spectroelectrochemical study of poly-3,4-ethylenedioxythiophene films in the presence of different supporting electrolytes

Steady-state absorption spectra of poly-3,4-ethylenedioxythiophene (PEDOT) films at different oxidation degrees and their differential cyclic voltabsorptograms are studied in 0.1 M LiClO4, Bu4NBF4, and Bu4NPF6 solutions in acetonitrile. Three major absorption bands are obtained in the film electronic spectra: a complex band with a pronounced maximum at lambda = 600 nm that corresponds to pi -> pi* electronic transitions in reduced fragments of a PEDOT film and two absorption bands (at lambda(max) = 850 nm and lambda(max) > 1100 nm) corresponding to two oxidized film fragments. It is shown that the position and shape of absorption bands are practically independent of the nature of dopant anions, which points to the absence of pronounced interactions with positively charged polymer fragments. An attempt is made to analyze the obtained spectroelectrochemical data qualitatively to estimate the extinction coefficients and concentrations of absorbing particles and their variation in the course of redox processes.