Solvatochromic responses and pH effects on the electronic spectra of some azo derivatives of 1-amino-2-hydroxy-4-naphthalenesulfonic acid

Synthesis and characterization of five arylazo derivatives of 1-amino-2-hydroxy-4-naphthalenesulfonic acid (H₂L¹) are reported. The UV/Vis absorption spectra of the parent compound (H₂L¹) and its arylazo derivatives (H₂L²–H₄L⁶) have been measured at room temperature in seven solvents of different polarities and with variable parameters. The electronic transitions were analyzed using SPSS program, linear regression technique and Kamlet–Taft’s equation to permit a good understanding of solvent-induced spectral shifts. The electronic absorption spectra of the prepared compounds containing different substituents were studied in aqueous solutions at different pH values. The pK values of the investigated compounds were evaluated spectrophotometrically. The prevailing acid species present at any pH range are judged from the constructed distribution diagrams.