SPECTROSCOPIC CHARACTERIZATION OF PEDOT:PSS CONDUCTING POLYMER BY RESONANCE RAMAN AND SERRS SPECTROSCOPIES

Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) synthesis was monitored by resonance Raman (RR) and surface-enhanced resonance Raman scattering (SERRS) spectroscopies and both the oxidation of the polymer and the effects of chain length were assessed by vibrational analysis. It was supported by theoretical models of oligomers, with charge ranging from 0 to +6 and size varying from 2 to 16 3,4-ethylenedioxythiophene (EDOT) repeat units, described through density functional theory. The symmetric CαCβ stretching band observed at ca. 1426 cm-1 shifts to higher wavenumbers for reaction times varying from 2 to 9 hours and stabilizes at intermediate wavenumbers for longer times. The former behavior was ascribed to the increase of concentration of oxidized species, which was corroborated by calculated wavenumbers for oligomer models when their charges changed from neutral to +6. The behavior observed for longer reaction times was associated with the growth of chains. It was also observed through SERRS spectroscopy that small chains of the polymer, obtained in the early time of the synthesis, adsorbs on gold nanoparticle surfaces through interactions via oxidized residues. In this way, RR and SERRS spectroscopies were valuable tools to follow the synthetic procedures of PEDOT:PSS, allowing the determination of the structural evolution of the polymer.