Optical and electrical characteristics of poly(3-alkylthiophene) and polydiphenylamine copolymers: Applications in light-emitting devices

In this work, poly (3-methylthiophene) (P3MT) or poly (3-octylthiophene) (P3OT) films were synthesized electrochemically with polydiphenylamine (PDFA), in layers and blended copolymers, in non-aqueous media through the oxidation of the monomers, 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. The electrochemical behaviors of as-prepared and partial dedoped films obtained by these methods was verified by cyclic voltammetry (CV) and have been characterized by UV–vis reflectance, resonance Raman, electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. Based on data obtained by UV–vis reflectance spectroscopy, it was possible to characterize the chemical species in the polymer matrix using the resonant Raman method. Both Raman and PL spectra results led to the characterization of three structures (aromatic, semi-quinone and quinone forms of thiophene rings) which formed the homopolymers and copolymers chain. The EPR measurements were taken to quantify the semi-quinone species stabilization at 298 and 77 K temperatures. The ionization potential (IP), electron affinity (E.A.) and gap energy (Eg) parameters were determined based on the technical analyses carried out.

► Characterization of three structures (aromatic, semi-quinone and quinone forms) of thiophene rings.
► Parameters for electrical and optical controls.
► Decrease in the bond length alternation.
► Semi-quinone species stabilization at 77 K.