Solvent polarity effect on photophysical properties of some aromatic azo dyes with focus on tautomeric and toxicity competition.

Edible dyes have become an essential part of modern life, widely appreciated for their safety and effectiveness in food coloring. Given the fundamental role of hydrogen bonding in chemical and biological systems, this study explores the photophysical properties of three commonly used aromatic azo food dyes-Ponceau 4R, Sunset Yellow, and Tartrazine-across both isotropic solvents and anisotropic environments. To better understand their environmental interactions in ground and excited states, the influence of media polarity on these dyes was also explored. The study further evaluated the applicability of the Kamlet-Abboud-Taft polarity scale in capturing these effects. The results highlight the crucial role of hydrogen bonding in facilitating azo-hydrazone tautomerization and enhancing structural resonance. Additionally, the toxicity of these dyes on kidney cells was assessed using the MTT assay, revealing that Ponceau 4R exhibits notable toxicity, primarily due to solute-solvent interactions. Notably, the hydrazone tautomeric form was identified as the predominant species in this dye.