A detailed UV–Vis spectral investigation of six azo dyes derived from benzoic- and cinnamic acids: experimental and theoretical insight

Six donor–${\pi }$–acceptor azo dyes, with altered donor- (p-hydroxyphenyl- and naphthalene-2-ol) and carboxylic based acceptor groups, were subjected to detailed solvatochromic and tautomeric investigation in different environments by experimental and theoretical approaches. Naphthalene-2-ol compounds exhibit azo–hydrazone tautomerism in all solvents, wherein benzoic- and cinnamic acid-based compounds appear in solutions as a complex system of neutral forms and corresponding carboxylates. p-Hydroxyphenyl based compounds adopt the azo form in all investigated solvents. A special focus was placed on the definition of the anionic species and the extent of the deprotonation in different alkaline solutions. Excellent agreement between theoretical and experimental data is attained