Add time:08/07/2019         Source:sciencedirect.com

4-Hydroxybenzo[h]quinolin-2-(1H)-one (IV) was synthesized from the cyclocondensation of 3-(naphthalen-1-ylamino)-3-oxopropanoic acid (I) or N,N′-di(naphthalen-1-yl)malonamide (II) and subsequently coupled with diazotized p-substituted aniline derivatives. The structures of the synthesized dyes were determined by spectroscopic and analytical methods. Solvent effects on the ultraviolet–visible absorption spectra of these novel azo dyes were studied in six pure organic solvents with different polarities. The color of the dyes is discussed with respect to the nature of substituents on the benzene ring. The tautomeric structures of the azo compounds were studied by 1H NMR spectroscopy in DMSO-d6 and CDCl3. The effects of acid and base on the visible absorption spectra of the dyes were also reported. Ionization constants, pKa, for these dyes were determined in 80 vol. % ethanol–water medium at room temperature and correlated with the substituent constant, σp.

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