FEATURES OF OPTICAL ABSORPTION AND STRUCTURE OF THIN FILMS OF POLYAMINOARENES

Abstract

Conjugated polymers, including polyaminoarenes, are actively used in many fields of research to improve sensors, optoelectronic and photonic devices, due to their unique physicochemical properties related to the presence of π-conjugated electronic bonds delocalized along the polymer chain. In recent years, there has been an increased interest in the use of conjugated polymers in sensors (chemosensors) as polymer films sensitive to the action of various gases. The peculiarities of the structure and optical absorption of thin films of polyaminoarenes – polyaniline and polyorthotoluidine on transparent glass substrates with an applied layer of tin oxide were studied. The method of chemical oxidative polymerization of aminoarenes in an aqueous solution of sulfuric acid under the action of an equimolar amount of ammonium persulfate was used to obtain the samples. The peculiarities of the optical absorption of thin films of polyaminoarenes on an optically transparent semiconductor surface in the wavelength range of 300–1100 nm were analyzed. It was established that the absorption spectra are characterized by the presence of broad bands in the region of 300–450 nm and 700–900 nm, caused by electronic transitions in the conjugated polymer system and the absorption of free charge carriers (polarons). Using Tauc's method, the optical band gap of polyaminoarenes (Eg) was determined. It was established that the values of Eg for polyaniline and polyorthotoluidine are 2.62±0.07 and 3.05±0.10 eV, respectively. The presence of a substituent in the benzene ring probably reduces the conjugation length of π-electron bonds, which leads to an increase in the energy of the transition from the valence band to the conduction band. Polyaminoarene films were tested for sensory sensitivity to vapors of organic solvents. It was found that the maximum sensitivity of polyaniline to nitrobenzene is observed at λ > 800 nm, and polyorthotoluidine to dimethylformamide – at λ > 700 nm. At the same time, the values of the optical band gap in the presence of organic molecules change little, which may indicate the physical nature of the adsorption of organic molecules on the surface of polyaminoarenes.