Extended aromatic π-electron conjugated dyes with three azo bonds and either one or two azulen-1-yl moieties in molecule. Synthesis and basicity

Azo dyes with either one or two identical or different azulen-1-yl moieties attached to the structure -N2-C6H4-N2-C6H4-N2- were prepared, the phenylene ring being either 1,3-1′,3′ or 1,4-1′,4′ disubstituted. The syntheses were accomplished in good yields via mono or bis diazotization of the corresponding anilines followed by the coupling with unsubstituted or alkyl substituted azulenes in acetic/acetate medium. The recorded electronic spectra of the synthesized compounds were analyzed and were compared with those of related compounds. The isosbestic points resulting from protonation of the azo compounds enabled pKa values to be determined. From these pKa values it is apparent that all studied compounds are very weak bases. The high solvatochromic property of the compounds with para,para-substituted phenylene groups reflects the hyperpolarizability of these compounds.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► New tris azo compounds containing one or two azulene moieties were prepared in good yields. ► The electronic spectra were interpreted and compared with those of similar compounds. ► Based on the isosbestic points, pKa values were determined of the azo compounds. ► The highly solvatochromic property of para,para-substituted phenylene groups reflects the hyperpolarizability of these compounds.