Electronic spectra, solvatochromic behaviour, and acidity constants of some new azocoumarin derivatives

The UV visible electronic spectra of some azocoumarin dyes derived from 6-a minocoumarin have been studied. The different bands observed have been assi gned to the proper electronic transitions. The compounds exist mainly in th e azo form but some of them exhibit an azo reversible arrow hydrazone tauto meric equilibrium. Solvatochromic behaviour of these compounds was investig ated by studying their visible spectra in pure and mixed organic solvents o f different characters. The longest wavelength band displayed by the azocou marin derivatives in DMF solution is assigned to an intermolecular CT trans ition. The solvated H-bonding complexes formed between DMF and 8-hydroxyqui noline derivatives were investigated. Delta G and K-f values of these compl exes have been determined. The acidity constants of six compounds were dete rmined from the spectra in aqueous-ethanolic solutions of varying pH values .