Solvatochromism, halochromism, and azo–hydrazone tautomerism in novel V‐shaped azo‐azine colorants – consolidated experimental and computational approach. (8th July 2016) - Choudhari, Amol S.
Abstract : The azo–hydrazone tautomerism, solvatochromism, and halochromism in four novel V‐shaped asymmetrical acceptor‐π‐donor‐π‐acceptor (A‐π‐D‐π‐A) compounds were examined. They contain 2, 7, 15, 16‐functionalised benzophenazine cores connected to the anchoring electron‐deficient phenyl core via azo linkers and 2, 7‐position fused with anthraquinone. These compounds derived from 2‐hydroxy‐1, 4‐napthaquinone (lawsone) have been prepared in moderate to good yields. The synthesis involved the diazotisation of substituted aromatic amines, coupling onto 2‐hydroxy‐1, 4‐napthaquinone, and further condensing the resulting azo compounds with 1, 2‐diaminoanthraquinone in acetic acid. The absorption wavelengths of the dyes in different solvents were in the range 500–720 nm. The spectral changes of the synthesised azo‐azine compounds in different pH indicated the formation of hydrazone tautomer in acidic pH and of azo tautomer in alkaline pH. Density functional theory was used to assess the tautomers in terms of geometry and position of the tautomeric equilibrium. Time‐dependent density functional theory calculations allowed us to assign the electronic transitions (>90%) of the low‐energy bands.