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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.

We designed and synthesized a new colorimetric chemosensor L based on the combination of 3-hydroxy-1, 4-dioxo-1, 4dihydronaphthalene-2-carbaldehyde 2 and diaminomaleonitrile 3 moiety. The recognition abilities of the probe with a range of metal ions were evaluated and their optical properties have been systematically investigated. The chemosensor L exhibited well defined naked -eye visible color changes from yellow to pink for Hg 2+ in acetonitrile. Other ions, including Na + , Ca 2+ , CO 2+ , Ni 2+ , Cu 2+ , Mn 2+ , Sn 2+ , Hg 2+ , Fe 3+ , and Th 4+ had a negligible influence on the probe behaviour. The limit of detection (LOD) were 1.1x10 -7 M using the UV-vis changes. The selective recognition of Hg 2+ ions, it forms a 1:1 stoichiometric complex involving naphthoquinone hydroxyl and diaminomaleonitrile nitrogen functionality. The complex formations were proposed to be in 1:1 ratio based on Job plot, 1 H NMR titrations, ESI -mass spectrometry analysis and DFT calculations. Test strips based on L were fabricated, which could act as a convenient and efficient Hg 2+ test kits. The results consistently indicated that the Lawsone -DAMN was the ideal sensor, which can be utilised to monitor Hg 2+ in solution over a wide pH range. Graphical AbstractA highly sensitive and selective chemosensor L exhibited well defined naked -eye visible color changes from yellow to pink for Hg 2+ in acetonitrile. The selective recognition of Hg 2+ ions, it forms a 1:1 stoichiometric complex involving naphthoquinone hydroxyl and diaminomaleonitrile nitrogen functionality.

The azo and styryl disperse dyes were synthesized by using 2-hydroxy-1,4-naphthoquinone (Lawsone) 1 and different substituted aromatic anilines and/or aldehydes. The structures of the dyes were confirmed using FT-IR, 1 H-NMR, MS, and HRMS spectral analysis. The dyes displayed a broad absorption maximum in the visible region between 426 and 490 nm. The present paper deals with the application of azo and styryl disperse dyes on polyester and nylon fiber, color characteristics, and fastness properties. The color strength (K/S value) has been found to be very good in all dyed polyester samples. The color fastness with respect to light exposure, washing, and rubbing was quite satisfactory for all dyed polyester compared to the nylon samples.

In this work, we have developed an efficient and simple protocol for the synthesis of novel A-π-D-π-A NIR azo dyes. The near infrared absorbing azo dyes were synthesized by using 2-hydroxy-1, 4 naphthoquinone (Lawsone) and different substituted aromatic primary amines. Furthermore, author developed push-pull chromophores of A-π-D-π-A type containing an electron-withdrawing azo core, phenazine moieties, and a hydroxyl group as electron donor. The benzo [a] quinoxalino [2,3-i] phenazin-5-ol moiety was introduced to make the system planer as well as to increase the π-conjugation. The optical properties of these dyes were studied in N, N-dimethylformamide (DMF).