NMR spectroscopic investigation of benzothiazolylacetonitrile azo dyes: CR7 substitution effect and semiempirical study

Ebead et al. had reported in the synthesis and the UV-Visible solvatochromism combined with semiempirical calculations to study the tautomerism of 1,3-benzothiazol-2-ylacetonitrile azo dyes [1]. In this study, 1,3-ben zothiazol-2-ylacetonitrile azo dyes (1-6) have been resynthesized, one and two dimensional H-1 and C-13 NMR, as well as absorption and emission spectra, were collected and interpreted. The obtained results were used to clarify the tautomerization phenomenon of these dyes. Predominantly, these dyes exist in Z-hydrazone form reinforced through intramolecular hydrogen bonding in deuterated chloroform. Substituents (R) in carbon7 (CR7) are the key player of the changes in H-1 and C-13 NMR chemical shifts, also in the absorption and emission wavelengths of benzothiazole azo dyes. Also, the relative photoluminescence quantum yields (PL QY) of these dyes (1-6) were estimated and related to the nature of substituents. Finally, PM6 semiempirical calculations were employed to confirm the preferred geometric structure and experimental NMR, absorption, and emission results.