Synthesis and physico-chemical properties of highly conjugated azo-aromatic systems. 4-(azulen-1-yl)-pyridines with mono- and bis azo-aromatic moieties at C3-position of azulene

• Published in: Dyes and pigments 2011-10, Vol.91 (1), p.55-61
• Main Authors: Razus, Alexandru C., Nica, Simona, Cristian, Liliana, Raicopol, Matei, Birzan, Liviu, Dragu, Andreea Eugenia
• Format: Article
• Language: English
• Subjects: Arylazo chromophores; Conjugation; Diazene azulenylpyridine; Dyes; Electrochemistry; Joining; NMR spectroscopy; Polarization; Push–pull compounds; Solvatochromism; Spectra; Stability; Synthesis; UV–Vis spectroscopy
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2011.02.008

Highly conjugated azo-aromatic systems have been prepared in high to moderate yields by linking mono- and bis-azo aromatic fragments to 4-(Rn-azulen-1-yl)-2,6-dimethyl-pyridine. The synthesized π-extended systems have been studied by NMR spectroscopy, UV–Vis and electrochemistry. Systematic increase of the conjugation along the azobenzene skeleton has affected the spectral properties of the azophenyl substituted 4-(azulen-1-yl)-pyridine. The synthesized compounds exhibit a bathochromic shift of the visible absorption maxima with the increase of the conjugating skeleton and introduction of an electron-withdrawing group. The electrochemical behavior revealed a high stability toward oxidation owing to the higher polarization induced by the azulenylpyridine moiety. [Display omitted] ► The synthesis and physico-chemical properties of highly conjugated azo-aromatic systems prepared by linking mono- and bis-azo aromatic fragments to 4-(Rn-azulen-1-yl)-2,6-dimethyl-pyridine is reported. ► Systematic increase of the conjugation along the azobenzene skeleton affected the spectral properties of the azophenyl substituted 4-(azulene-1-yl)-pyridine, namely a bathochromic shift of the visible absorption maxima. ► The solvatochromic behavior of both mono- and bis-azo diazene showed that by changing the solvent polarity, the λ max value is less influenced, the influence of the solvent on the electronic molecular system being reduced due the presence of two moieties which can act as push–pull systems. ► Owing to higher polarization, the azulenylpyridine diazene exhibit high oxidation potential.