Merocyanine dyes containing an isoxazolone nucleus: Synthesis, X-ray crystal structures, spectroscopic properties and DFT studies

Two merocyanine dyes, each with an isoxazolone nucleus, were synthesized and characterized by NMR, IR, UV-Vis spectroscopy, elemental analyses and single X-ray diffraction. Crystallographic data revealed that one dye crystallized in an orthorhombic system, Cmca space group, while the other dye crystallized in a monoclinic system, P2 ₁/n space group. In the case of both dyes, the molecules adopted the most stable ketonic tautomeric form, and the crystal packing was stabilized by hydrogen bonds and π-π stacking interactions. The absorption spectra of the dyes in various solvents of different polarities were studied at room temperature. The equilibrium geometries, vibrational data and electronic spectra of the compounds were also investigated by the B3LYP method. Importantly, the predicted results fit to the experimental data, showing that this quantum chemical technology is an efficient approach to predict the properties of merocyanine dyes.