Towards analytical application of electrochromic polypyrrole layers modified by phenothiazine derivatives

Electrochromism is the phenomenon, which is based on the change of material color when particular voltage is applied to electrochemical system. This feature is of high importance for a wide range of actuating devices such as smart windows, screens, thermal modulators and various sensors. During this research we have formed and investigated polypyrrole (Ppy) based layers, which were electrochemically deposited on the indium tin oxide coated glass in the presence of three phenothiazine (PT) derivatives - methylene blue (MB), azure A (AA), and thionine (TH). The surface morphology of the coatings was determined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). It was found that the thickness of the surface irregularities ranged from 1 to 3 µm. The reflection absorption infrared spectroscopy (RAIRS) was chosen for the evaluation of the layer due to the possibility to measure reflection spectra of thin layers avoiding influence of the glass substrate present under the ITO layer. Polypyrrole and poly(Azure A) (Ppy-PAA) layer was the thickest one and non-translucent, therefore, it was not suitable for optical evaluation. The polypyrrole and poly(methylene blue) (Ppy-PMB) and polypyrrole and polythionine (Ppy-PTH) layers also were analyzed by cyclic voltammetry and chronoamperometry methods. The applicability of Ppy-PMB, Ppy-PAA, and Ppy-PTH in chemical sensing was evaluated. The investigated polymeric coatings exhibited electrochromic properties (color change at different potential), reacted to pH changes and to ascorbic acid concentration.