Crystal structures, solvatochromisms and DFT computations of three disperse azo dyes having the same azobenzene skeleton

• Two pairs of isomeric benzothiazole and benzisothiazole based dyes are described.
• Single-crystal structures of three heterocyclic dyes 1–3 are included.
• Solvatochromism and acid-base discoloration of these dyes are studied.
• Benzisothiazole based dyes show higher thermal stability and larger λmax.

Three disperse azo dyes having the same 4-nitrobenzene/azo/4-aminobenzene skeleton but different color have been structurally and spectrally characterized and compared in this paper. X-ray single-crystal diffraction analysis of compound 3 reveals that it has a planar molecular conformation between the azo and the nitrobenzene units. However, severely twisted aminoazobenzene structures in compounds 1 and 2 are observed because of the steric hindrance effect of ortho chloro and bromo groups. Electronic spectra of 1–3 are closely related to their molecular structures, which demonstrate that the presence of different substituted groups and the spatial crowding effect in the aminoazobenzene backbone leads to the significant alterations of bathochromic and hypochromatic shifts. In addition, theoretic computational studies as well as solvatochromisms for three azo dyes have been included.