Construction of benzothiazole/pyridone based bi-heterocyclic dyes and their NiII and CuII complexes

Abstract A family of bi-heterocyclic dyes have been first synthesized by using heterocyclic pyridone and benzothiazole components. UV−Vis spectral analyses reveal distinct spectral behaviors depending on the introduced electron-withdrawing and electron-donating groups in the benzothiazol ring as well as the polarity of solvents. Namely, nitrobenzothiazol based bi-heterocyclic dyes display more obvious solvatochromism compared with both methylbenzothiazol based ones and previously reported azobenzene based half-heterocyclic pyridone dyes. More interestingly, 1 H NMR and UV−Vis spectral results as well as single-crystal structures manifest that these dyes are in the hydrazone form in the solid state and in the non-polar solvents. However, they adopt dominating azo form in polar solvents and it can be transformed to the hydrazone form in the acidic condition, which are both different from all known half-heterocyclic pyridone dyes. In addition, transformation from hydrazone to deprotonated azo form can be achieved via metal-ion complexation, and four Ni II and Cu II complexes with different pyridone N -tails have been structurally characterized. It is noted that the ligands adopt different tridentate coordination fashions with Ni II and Cu II ions and a rare tetranuclear Cu II complex with equal Cu⋯Cu separation is obtained.