Effect of Solvent on Azo-Hydrazonetautomerism of 2-Hydroxy-5-(4-Nitrophenylazo) Benzaldehyde

Azo dye has been synthesized having Donor-p-Acceptor (D-p-A) system to study the effect of solvent on the azo-hydrazone tautomerism. The relative stabilities of azo and hydrazone tautomer are examined by means of UV-Vis spectroscopic technique and are correlated with the solvent properties in neat organic solvents and in different binary solvent mixture. Due to the presence of intramolecular H-bonding, azo form predominates in most of the nonpolar and polar protic solvents. Presence of low energy CT band in basic solvents like DMF is due to the predominance of anionic hydrazone form stabilized through the lengthening of the conjugated system. In the binary solvent mixtures, preferential solvation occurs due to specific solute-solvent interaction. The microenvironment surrounding the dye molecules played a major role in the stability of one tautomer relative to the other.A good understanding of the properties of specific azo dyes in different medium lead to the design of new azo dye molecules with targeted properties for applications in specific areas