Synthesis and Application of Spiropyrane-Based Photochromic Dyes for Wool

Suffered from poor substantivity and water solubility, the direct application of spiropyrane-based photochromic dyes to protein fibers is limited. Herein this paper reported the synthesis of water-soluble photochromic dyes for woolen fiber coloration with good water solubility, substantivity, and washing fastness. The spiropyrane-based photochromic dyes were synthesized by a three-step reaction with sulfonate group as water-soluble group. Moreover, N-alkyl or aryl groups of variable size were introduced into the dyes to tailor the substantivity towards wool fiber and the chemical structures were confirmed by H-1-NMR and mass spectrum. Under optimum dyeing condition, the dyes showed high affinity toward wool fiber in the order of BnSP > HdSP > MeSP. Upon UV irradiation, the CIE chromaticity coordinates of the photochromism wools shifted from white region (0.33, 0.35) to the red region for MeSP (0.39, 0.34) and HdSP (0.39, 0.38), and blue region for BnSP (0.30, 0.31). A more improved washing fastness for the wools dyed with BnSP and HdSP (grade 4-5) was observed than the one dyed with MeSP (grade 4). The revealed structure-property relationships in the spiropyrane-based photochromic dyes provide a general guideline to design new photochromic dyes for wool fiber coloration.