A comprehensive spectroscopic, solvatochromic and photochemical analysis of 5-hydroxyquinoline and 8-hydroxyquinoline mono-azo dyes.

• Novel azo dyes based on 5-hydroxyquinoline and their well-known 8HQ analogues were synthesized. • Partially deuteration technique in 13C NMR spectroscopy was used in order to investigate the tautomerization in these azo dyes. • The study of solvatochromism in azo dyes strengthens explanation of tautomerism disclosing the effect of solvent used on these phenomena. • Photochromism phenomena justifies E/Z isomerization in the studied azo dyes. Image, graphical abstract A series of novel substituted-azo dyes 8-(aryldiazenyl)quinolin-5-ol (5a-i) were synthesized by the coupling reaction of 5-hydroxyquinoline with diazotized aniline derivatives in the presence of NaNO 2 in HCl/H 2 O mixture. The study of the spectroscopic and solvatochromic properties were performed by FT-IR, 1H and 13C-NMR and UV-Visible spectroscopies. The tautomerism of these dyes was studied using the deuteration technique and solvatochromic measurements. Photochromic properties of these 5-hydroxyquinoline azo dyes were also examined via E/Z and Z/E photochemical isomerization reactions and compared with the existing 8-hydroxyquinoline analogous. The novel substituted-azo dyes exhibited higher Z/E thermal isomerization rates and have larger absorbance wavelength range than their 8-hydroxyquinoline analogous, making them potential molecular switches. [ABSTRACT FROM AUTHOR]