Effect of substituents on the absorption spectra andpK values of some azo dyes derived from thiobarbituric acid

Abstract

A series of azo dyes from aromatic diazonium salts and thiobarbituric acid have been synthesised and their UV-Vis spectra have been recorded in neutral media and at two extreme pH values. The absorption maxima have been correlated with Swain-Lupton's F and R parameters using Williams-Norrington's weightage factors. The pK values of the dyes have also been determined and are highly predictable using Williams-Norrington's model.

A comprehensive spectroscopic, solvatochromic and photochemical analysis of 5-hydroxyquinoline and 8-hydroxyquinoline mono-azo dyes

“…Furthermore, among dyes 4c, 4h and 4i , which have hypsochromic shift relative to 4d , compound 4h shows a small shift. A similar hypsochromic shifts were noticed in azo dyes with chlorine in metaposition [82] , nitro -substituted ( ortho -or para -) [83] and crowding substituents at the phenyl ring [84] . However, it could be concluded that bathochromic or hypsochromic effects caused by the addition of a substituent is highly dependent on the applied solvent [85] .…”