Synthesis, spectral characterization, and theoretical investigations of a new azo-stilbene dye for acrylic resins

Abstract

This paper presents the synthesis of a new symmetrical disazo direct dye with good coloring properties for acrylic resins and several theoretical approaches to choose the best simulation method of the dye structure and spectra. The synthesized dye contains 4,4′-diaminostilbene-2,2′-disulfonic acid, as middle component and 2,7-dihydroxynaphthalene, as coupling component. It was analyzed by thin-layer chromatography (TLC), FT/IR, UV/VIS, 1H NMR, 13C NMR spectroscopy, and HRMS spectrometry. The molecular dye structure was investigated using molecular mechanics and the Density Functional Theory (DFT) approach at the B3LYP/6-31G(d,p), B3LYP/6-31+G(d,p) and B3PW91/6-311G(d,p) levels. Theoretical vibrational frequencies and structural parameters were calculated and the dye UV/VIS spectrum was simulated using the CIS, TD and ZINDO methods and compared with the experimental data. The ZINDO approach gave better maximum absorption predicted values compared to the CIS and TD methods. A generally good agreement between the experimental and theoretical computed absorption maxima and excellent correspondences between the experimental and calculated vibrational frequencies and chemical shifts were found. The experimental and simulated vibrational, UV/VIS and 13C NMR spectra confirmed the trans-configuration form of the π-bonds of the investigated dye. The CIEL∗a∗b∗ color space was used in all color measurements for the dye in powder and its mixtures with a water-based acrylic resin and confirmed the color properties of the newly synthesized dye.