Indole-containing new types of dyes and their UV–vis and NMR spectra and electronic structures: Experimental and theoretical study

• Four indole-based colorants were synthesized.
• NMR and UV–vis spectra were provided and analyzed.
• Solvatochromic effect of colorants was investigated.
• HOMO–LUMO orbital and energy gaps of the molecules were calculated.
• Tautomerization of colorants was analyzed.

Indole containing dyes were synthesized via a simple method with high yield. These molecules have different colors and UV–vis spectra of them were recorded. Impact of solvents on absorbances was investigated and it was observed that basic solvent such as DMF and pyridine have blue shift. TD-DFT calculations were done and results were compared with experimental data. NMR data of molecules were analyzed and tautomeric forms of colorants and their ratio were determined. It was find out that two tautomers might be formed in solution, called indole and indolenine form. HOMO-LUMO and energy gaps were calculated and plotted. Furthermore, molecular electrostatic potentials were simulated to find out electrophilic and nucleophilic regions.

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