We report here the synthesis of (6Z)-4-[(E)-(4-ethylphenyl)diazenyl]11-6-[[(2-hydroxy-5-methylphenyl)aminolmethylidene}cyclohexa-2,4-dien-1-one by the condensation reaction between 2-amino-4-methylphenol and 5-[(E)-(4-ethylphenyl)diazenyl]-2-hydroxybenzaldehyde in equimolar ratio in Me0H and characterized by elemental analyses, infrared, electronic, mass,H-1 and C-13 NMR spectroscopy. Molecular structure of the azo-enamine dye was also determined by single crystal X-ray diffraction technique. X-ray investigation of the dye showed that azo-enamine tautomer is favoured in the solid state. There is an intramolecular hydrogen bonding (N3-H center dot center dot center dot O1) in the molecule forming a S(6) graph set motif. Additionally, there is an intermolecular O2-H center dot center dot center dot O1 hydrogen bonding in the structure. The same intermolecular hydrogen bonding contacts are extended between the other symmetry-related molecules in their respective planes to form a 1D hydrogen bond chain. Self-isomerisation via intramolecular proton transfer was investigated by UV-Vis. spectra and theoretical calculations. Effects of polarity and temperature on UV-Vis. spectra were examined in detail. Moreover, acid dissociation properties of the polydentate compound was investigated at 25 +/- 0.1 degrees C. (c) 2014 Elsevier B.V. All rights reserved.