Optical and Structural Characterization of Poly(3-methylthiophene) (P3MT) Electrochemically Synthesized

In this work was synthesized electrochemically the poly(3-methylthiophene) (P3MT) on transparent conductive substrates of F-doped tin oxide (FTO), using as supporting electrolyte Et4NBF4 or LiClO4 in acetonitrile. To dedope the material, the samples were reduced electrochemically and chemically (in NH4OH solution). The films were characterized by electron paramagnetic resonance spectroscopy (EPR) and infrared spectroscopy (FTIR) and their optical properties examined by ultraviolet-visible absorption spectroscopy (UV-Vis) and photoluminescence (PL). Scanning electron microscopy (SEM) images of the first synthesized samples were performed to verify the degree of homogeneity of them. The FTIR spectra show the characteristic features of P3MT and, together with the results of EPR, allowed to evaluate the charge carriers and to identify benzoid and quinoid structures in the formation of chains. The UV-Vis absorption spectra helped to obtain the average gap energy of P3MT presenting the π-π* transition band and a bipolaron band. In the PL spectra, with variation of excitation power, studies were performed through the fit with Gaussian functions, given the strong probability of the existence of two distinct contributions in the formation of the emission spectra. These two contributions were assigned to the emission of mixed chains (Gaussian centered at higher energy) and emission of benzoid chains (Gaussian of lower energy) in the formed polymeric material.