Spectral characterization and computational studies of some new synthesized 3-arylazo-4-hydroxybenzo[h]quinolin-2(1H)-one dyes

Abstract

A series of substituted anilines with different electron releasing and electron accepting substituents have been diazotized and coupled with 4-hydroxybenzo[h]quinoline-2(1H)-one in basic ethanol solution at 0-5°C. The structures of these newly synthesized azo dyes were assigned by IR, 1H NMR and Mass spectroscopic analyses. The UV-vis absorption spectra of the dyes, recorded in solvents with different polarities, showed no distinct change owing to their strong intramolecular hydrogen- bonding interactions. The visible absorption spectra along with 1H NMR findings of all the 4-hydroxyquinolin-2-one dyes revealed that there is a mixture of two geometrical isomers E and Z of keto-hydrazo-keto tautomeric form in the solution state in solvents with different polarities. The effects of acid and base on the visible absorption spectra of the of the dyes in ethanol were also studied and showed that the spectral changes are clearly dependent upon the protonation-deprotonation of the dye molecules. The geometries of the azo and hydrazone tautomeric forms of the dyes were optimized at B3LYP/6-31G(d) level of theory. DFT calculations were employed to calculate the stability of tautomeric forms of prepared dyes both in gas phase and in the solution state and the results agreed well with 1H NMR spectroscopic results.