New heterocyclic green, blue and orange dyes from indazole: Synthesis, tautomerism, alkylation studies, spectroscopic characterization and DFT/TD-DFT calculations

• Some new green, blue and orange dyes were synthesized from indazole.
• The optical and solvatochromic properties of the dyes were investigated.
• Tautomerism, oxidation and alkylation reactions were examined in these compounds.
• DFT/TD-DFT calculations of the dyes are performed at the B3LYP/6-311++G(d,p) level.

Tautomerism and alkylation studies on the green intermediate 2-(5-hydroxyimino-1-methyl-4,5-dihydro-1H-4-indazolyliden)-2-phenylacetonitrile led to the synthesis of new heterocyclic green, blue and orange dyes in high yields. The structures of all newly synthesized compounds were confirmed by spectral and analytical data. The optical properties of the dyes were spectrally characterized by using a UV–vis spectrophotometer and results show that they exhibited interesting photophysical properties. Solvent effects on the absorption spectra of these dyes have been studied and the absorption band in polar solvents undergoes a red shift. Density functional theory calculations of the dyes were performed to provide the optimized geometries and relevant frontier orbitals. Calculated electronic absorption spectra were also obtained by time-dependent density functional theory method.

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