2-Amino-4-chloro-5-formylthiophene-3-carbonitrile derived azo dyes

•Six thiophene-based heterocyclic azo dyes are described.•Push-pull electron effect of N–substituents impacts their charge transition.•UV–vis spectra and solvatochromism behavior are described.•They are compared with 4-nitro-4′-amino-azobenzene dyes on λmax, ε and FWHM.

Six azo dyes derived from the common 2-amino-4-chloro-5-formylthiophene-3-carbonitrile unit and different aniline based couplers were synthesized by the traditional diazotization-coupling strategy. Solvatochromism has been studied for this family of donor−π−acceptor heterocyclic azo dyes. Furthermore, UV–Vis spectral comparisons (maximum absorption wavelength, molar extinction coefficient and full width at half maximum) have been made between the six new azo dyes reported in this work and four previously reported 4-nitro-4′-amino-azobenzene disperse dyes. In addition, X-ray single-crystal structure of one representative azo dye has been included, which constitutes the first structural report on azo dyes containing the 2-amino-4-chloro-5-formylthiophene-3-carbonitrile diazo component.

Graphical abstractSix heterocyclic azo dyes having the common thiophene diazo moiety with three electron-withdrawing groups (CN, Cl, CHO) and different aniline based couplers are described, and they are compared with 4-nitro-4′-amino-azobenzene based disperse dyes on their λmax, ε and FWHM values.Figure optionsDownload full-size imageDownload as PowerPoint slide