Design, synthesis and spectroscopic characterisation of novel azo dyes incorporating benzimidazole moiety

This study describes the design, synthesis and characterisation of benzimidazole-derived azo dyes. Ten novel azo acid dyes were synthesized from benzimidazole derivatives using H-acid, Gamma acid, J-acid and Tobias acid as the coupling components. The synthesized intermediates and the dyes were characterised and their properties and structures confirmed using UV–Visible, FT-IR and 1H-NMR spectroscopic techniques. The electronic absorption spectra of the synthesized dyes were within the wavelength range of 492‒660 nm in DMF at a uniform absorption intensity ranging from (0.18‒2.03) × 104 L.mol− 1 cm− 1 The FT-IR spectra of all the dyes showed peaks within the range of 3365‒3712 (cm− 1) corresponding to O–H stretching; 3425‒3362 (cm− 1) indicating N–H stretching; 1643‒1476 (cm− 1) confirming the presence of (–N = N-) and 1431.3‒1185 (cm− 1) which are attributed to (S = O) stretching. The 1H-NMR (δ) spectra of the dyes confirmed the presence of methyne (-CH-) groups between the range of 1.50‒1.89 ppm; methylene (-CH2-) groups between 1.27 and 1.47 ppm; methyl (-CH3-) groups between 1.16 and 1.20 ppm; aromatic protons between 6.78 and 8.63 ppm and carboxylic acid (-RCOOH) group between 10.36 and 12.78 ppm.