NMR analysis of Nile Blue (C. I. Basic Blue 12) and Thionine (C. I. 52000) in solution

The dyes Nile Blue (C. I. Basic Blue 12) and Thionine (C. I. 52000) were examined in both ionic and neutral forms in different solvents using NMR and UV–visible spectroscopy to firmly establish the structures of the molecules and to assess the nature and extent of their aggregation. 1H and 13C NMR assignments and chemical shift data were used, together with nuclear Overhauser effect information, to propose a self-assembly structure. These data were supplemented with variable temperature, dilution and diffusion-based experimental results using 1H NMR spectroscopy thereby enabling extended aggregate structures to be assessed in terms of the relative strength of self-association and the extent to which extended aggregates could form.