Solvatochromism and linear solvation energy relationship of diol- and proline-functionalized azo dyes using the Kamlet–Taft and Catalán solvent parameter sets

Abstract

New donor–acceptor-substituted azo dyes, such as 2-({4-[(E)-(2,4-dinitrophenyl)diazenyl]-2-nitrophenyl}amino)propane-1,3-diol, (2S)-1-{4-[(E)-(2,4-dinitrophenyl)diazenyl]-2-nitrophenyl}-pyrrolidine-2-carboxylic acid and methyl-(2S)-1-{4-[(E)-(2,4-dinitrophenyl)diazenyl]-2-nitrophenyl}pyrrolidine-2-carboxylate have been obtained in a single step by nucleophilic aromatic substitution of (E)-1-(2,4-dinitrophenyl)-2-(4-fluoro-3-nitrophenyl)diazene with 2-aminopropane-1,3-diol, (S)-proline and (S)-proline methyl ester hydrochloride. The solvatochromism of the diol- and (S)-proline-methyl-ester-containing azo dye was studied and analysed using the empirical Kamlet–Taft and Catalán solvent parameter set. The dyes undergo a reversible protonation–deprotonation equilibrium in a concentration range of 5–12 M hydrochloric acid. The UV/Vis absorption spectra show a bathochromic shift with increasing acid strength of the medium.