Synthesis, Characterization, and Application of pH-Sensitive Monoazo Heterocyclic Disperse Dyes: A Study of Solvatochromism, DFT Analysis, and Biological Activity

In the present work, five monoazo heterocyclic disperse dyes PY₁–PY₅ were synthesized in good yield. A 2-amino-3-hydroxypyridine was used as a coupling component with five distinct heterocyclic diazonium salts. All the dyes are new except the dye PY₄. The obtained colorants were characterized by melting point, ¹H-NMR, FT-IR, UV–Vis, FAB-LRMS, and FAB-HRMS. The main skeletons of the dyes PY₁, PY₃, and PY₄ were further confirmed by ¹³C-NMR (BB), ¹H–¹H COSY, ¹H–¹³C HSQC, and ¹H–¹³C HMBC. The effect of pH variation on the λ_max of these colorants was assessed in methanol and DMSO. Their solvatochromism analyses were performed in various organic solvents, e.g., acetic acid, methanol, acetone, acetonitrile, dimethyl sulfoxide, and dimethyl formamide. The geometries of the dyes were optimized at the B3LYP/6-311G (d,p) level, and their electronic excitation properties were determined using time-dependent density functional theory. The computed data were in good agreement with the experimental data. These colorants were applied to polyester fabric as disperse dyes and evaluated for build-up study along with complete observation of their fastness to water, washing, sublimation, rubbing, perspiration, and light. The antimicrobial exploration of these dyes was performed in detail against human pathogenic fungi including Aspergillus fumigatus, Candida glabrata, Candida albicans and Trichophyton rubrum. The dye PY₅ was found to have promising inhibition against all the human pathogenic fungi used.

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