Substituents-triggered modulation of structure and alkali resistance in cyano-based disperse dyes

Alkali-resistant disperse dyes have garnered significant interest due to their numerous advantages in alkaline one-bath dyeing procedures. Herein, six cyano-based disperse dyes (D1-D6) with either 2-aminobenzothiazole or 2-amino-6-nitrobenzothiazole, as well as N-substituted anilines as coupling components, were designed and synthesized to investigate the effect of substituents and pi-pi conjugation of the alkali-resistant stability of dyes. High-performance liquid chromatography (HPLC) was used to monitor the dye hydrolysis behavior, indicating that dyes with strong intramolecular pi-pi conjugation and bulky benzyl substituents on the n-phenylamine substituent exhibited good alkaline resistance. The hydrolysis processes of cyano disperse dyes under alkaline conditions were consistent with SN2 Nucleophilic substitution, and followed first-order reaction kinetics. Furthermore, PET fabrics were dyed with D1-D3 under various alkaline conditions, proving that D2 and D3 possessed good dyeing performance even under a 5 g/L NaOH dye bath. Our study contributes valuable insights into the relationship between molecular structure and alkali resistance in cyanide disperse dyes, offering practical guidance for enhancing the performance of such dyes.