Spectroscopic analysis of the structure and stability of two electrochemically synthesized poly(3-alkylthiophene)s

In this work, poly (3-methylthiophene) (P3MT) and poly (3-octylthiophene) (P3OT) films were synthesized electrochemically in non-aqueous media through the oxidation of the monomers, (3-methylthiophene and 3-octylthiophene), using a standard three-electrode cell in acetonitrile with 0.100 mol L-1 LiClO4. The polymeric thin films were deposited on platinum plates for optimal quality control of the process. It was observed that the material as-prepared for the anodic electropolymerization undergoes a natural process of de-protonation as a function of time. Moreover, the partial dedoped form, obtained in NH4OH solution, presents a good chemically stabilite form but, when radiated with blue light again becomes unstable. Films obtained by these methods have been characterized by cyclic voltammetry, Raman and photoluminescence spectroscopy. Both Raman and photoluminescence (PL) spectra results led to the characterization of two structures (pristine and non-pristine forms of thiophene rings) which formed the P3MT and P3OT polymer chain. These results were associated with the stabilization of pristine chains and mixed chains (non-pristine structures), radical cation and dication forms, in the polymeric film. Their bands in the Raman and PL spectra are wide and asymmetric and their adjustments by Gaussian functions were necessary, indicating that there are three distinct contributions to the vibration and two to the emission spectra in the formed polymeric material.