Synthesis, characterization, and polyester dyeing performance of azo barbituric and thiobarbituric acid disperse dyes

This study explores the synthesis, characterization, and application of 23 azo disperse dyes synthesized based on barbituric and thiobarbituric acid derivatives for polyester coloration. The dyes were synthesized via the coupling of diazotized aniline derivatives with barbituric and thiobarbituric acid derivatives. The structures of these synthesized dyes are assigned using FT-IR and¹H NMR spectroscopy. UV-Vis spectroscopy revealed absorption maxima ranging from 360 to 440 nm, with good correlation between experimental and theoretical values calculated using TD-DFT. The dyes exhibited significant pH-dependent spectral shifts, demonstrating potential as pH indicators. Application to polyester fabrics showed excellent wash fastness (rating 5) for all dyes, with varying results for perspiration, scorch, and light fastness. The dyes demonstrate dye exhaustion ranging from 43.6 to 92.5%, with color strength (K/S) values up to 22.00, while computational insights from DFT calculations provide deep understanding of structure-property relationships. The study demonstrated that substituent type and position significantly influenced dye properties and performance. Notably, dye 17 (4-OCH₃) exhibited the highest K/S (21.40) and K/S_sum (349.05) values, correlating with its low HOMO-LUMO gap (0.1177 eV). These findings contribute to understanding the structure-property relationshipsin azo disperse dyes and their application in polyester dyeing.