Visualized fabric discoloration of bi-heterocyclic hydrazone dyes

Abstract A series of bi-heterocyclic hydrazone dyes have been synthesized by classic diazotization reactions between 2-amino-3-cyano-4-chloro-5-formylthiophene and five pyridine-2,6-dione based coupling components, including two acetal products undergoing dimethylacetalization of aldehyde group in the presence of methanol and glacial acetic acid. 1 H NMR spectral and single-crystal X–ray diffraction studies reveal the presence of hydrazone tautomeric form for this family of dyes both in solution and in the solid state. More interestingly, visualized fabric discoloration has been firstly observed for this family of dyes on five representative fibers (Polyester, Nylon, Silk, Wool and Cotton) under different pH values. It is believed that the proton transfer originated from the azo-hydrazone tautomerism is responsible for the above-mentioned solvatochromism and fabric discoloration.