Disazo dyes containing pyrazole and indole moieties: Synthesis, characterization, absorption characteristics, theoretical calculations, structural and electronic properties

The newly synthesized thirteen disperse disazo dyes 3a-3m were prepared by diazotization of 5-amino-4-arylazo-3-methyl-1H-pyrazoles 2a-2m and coupling with 2-methyl indole. Their structures were characterized by UV-vis, FT-IR, H-1 NMR and elemental analysis. Solvatochromic properties in different solvents were studied. Also, the effects of acid and base on the visible absorption spectra of the dyes were informed. Besides, the theoretical vibrational frequencies have been scaled and compared with the corresponding experimental data. H-1 NMR spectra were recorded and chemical shifts of the molecules were compared to TMS by using the Gauge Independent Atomic Orbital (MO) method. A study on the electronic and optical properties, absorption wavelengths, excitation energy and dipole moment is performed using DFT method. NBO analysis is carried out to picture the charge transfer between the localized bonds and lone pairs. All spectroscopic properties examined with the experimental techniques were supported with the computed results. (C) 2016 Elsevier B.V. All rights reserved.