Synthesis of 5-azo-8-hydroxy-2-methylquinoline dyes and relevant spectroscopic, electrochemical and computational studies

•Twenty four derivatives of 5-azo-8-hydroxy-2-methylquinoline have been synthesized.•Two of novel dyes have been structurally characterized by X-ray crystallography.•The solvents effects indicated the existence of azo hydrazone tautomerism.•The cyclic voltammetry studies show similar redox properties for all selected dyes.

Twenty four derivatives of 5-azo-8-hydroxy-2-methylquinoline dyes with twenty three novel structures have been synthesized in an efficient one-pot synthesis protocol. Their properties were characterized by the combination of IR, NMR, MS, HRMS, GC-MS and electronic absorption spectroscopy. Two of the novel dyes have been synthesized as hydrochloride salts and structurally characterized by X-ray crystallography. The oxidation and reduction properties of selected 5-azo-8-hydroxy-2-methylquinoline dyes were studied using cyclic voltammetry. The measured visible absorption spectra of the dyes were discussed regarding the effects of substituent, varying pH and solvent upon their absorption ability. The molecular orbitals of the selected dyes have been calculated by density functional theory (DFT), which demonstrated that the HOMO orbitals were concentrated in the aromatic rings and in the azo part (–N=N–). The calculated HOMO and LUMO energies are in consistence with redox behavior of azoquinolines. The obtained dyes were successfully incorporated into polyester fabrics and their light fastness properties were evaluated.

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