Eletrossíntese de um polímero D-A-D contendo benzotiadiazol com potencial para aplicação em dispositivos eletrocrômicos

Abstract

Conjugated polymers have been standing out as a new generation of electrochromic materials, featuring low response time, high coloration efficiency, ability to changing their optoelectronic properties through chemical structure and the development of flexible devices. The design of the chemical structure may involve the combination of electron-rich and deficient units (donor-acceptor concept) generating an internal charge transfer that allows fine-tuning of optoelectronic properties. One of the synthesis methodologies involve the polymerization electrochemically conducted on the surface of an electrode, allowing the control of the characteristics of the synthesized thin films, as well as a higher degree of purity and reproducibility in a fast and relatively simple process. In this study, the electrosynthesis and optical, electrochemical and morphological properties of a D-A-D polymer, Poly(4,7- di(thiophen-2-yl)-2,1,3-benzothiadiazole) – PTBT and its performance as active material on a electrochromic solid-state device, were analyzed. Electrochemical analysis revealed n-doping in the presence of NBu4+ cations, as well as an ion-trapping effect in electrolyte containing lithium ions, as also observed by the irreversible change in the absorption spectrum. Spectroelectrochemical measurements revealed the electrochromic activity at positive potentials (optical contrasts of 19% at 560 nm and 54% at 1000 nm), with a color change from purple-blue (neutral state) to a state of higher transmittance (oxidized state). It was observed that changes in morphology might be obtained as a function of the parameters or electrochemical synthesis methods. Preliminary analyzes performed with flexible solid-state electrochromic device based on PTBT demonstrated promising values of coloration efficiency at 450 nm, of 49 cm2 C-1.