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Synthesis and characterization of a new soluble polythiophene derivative and its electrochromic application

Tarkuç, Simge
The Knorr-Paal reaction of 1,4-di(2-thienyl)-1,4-butanedione with aniline to yield 1-phenyl-2,5-di(2-thienyl)-1H-pyrrole (PTP) was performed in the presence of catalytical amounts of p-toluenesulfonic acid (PTSA). Chemical polymerization of the monomer yielded a soluble polymer. Structures of both the monomer and the polymer were investigated by Nuclear Magnetic Resonance (1H and 13C NMR) and Fourier Transform Infrared (FTIR) Spectroscopy. The average molecular weight of the chemically synthesized polymer was determined by Gel Permeation Chromatography (GPC) as Mn = 7.2 x 103 g/mol. The electrochemical oxidative polymerization of PTP was carried out via potentiodynamic electrolysis in the presence of LiClO4, NaClO4 (1:1) being the supporting electrolyte in acetonitrile. Electrochemical copolymerization of PTP with 3,4-ethylenedioxythiophene (EDOT) was carried out in acetonitrile (ACN)/ NaClO4/LiClO4 (0.1M) solvent-electrolyte couple system via potentiodynamic electrolysis. Cyclic voltammetry was used to investigate electrochemical behavior of the monomer and redox reactions of conducting polymers. Conductivities of films of the polymers were measured by four-probe technique. Surface morphologies of the films were investigated by Scanning Electron Microscope (SEM). Electrochromic properties of the conducting polymers were investigated via spectroelectrochemistry, kinetic and colorimetry studies. Spectroelectrochemical analysis of P(PTP) revealed electronic transitions at 413, 600 and 900 nm corresponding to π-π* transition, polaron, and bipolaron band formations, respectively. The spectroelectrochemical behavior of the P(PTP-co-EDOT) in comparison to those of the respective homopolymers revealed solid evidence of copolymerization based upon the differences in the spectral signatures. Switching time of the polymers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at the maximum contrast point. As an application, absorption/transmission type electrochromic devices with ITO/homopolymer(copolymer)/gel electrolyte/PEDOT/ITO configuration was constructed, where homopolymer (copolymer) and PEDOT functioned as the anodically and the cathodically coloring layers, respectively. Spectroelectrochemistry, switching ability and open circuit memory of the devices were investigated. The results revealed that these devices have good switching times, reasonable contrasts and optical memories.