The effect of first-row transition metals on the photophysical and structural properties of the fluorescent dye syn-(Me,Me)bimane

Syn-Bimanes are a family of fluorescent heterocyclic¹ compounds, which are mainly used as fluorescent dyes in biological systems. Although they have been in use for over 40 years, their coordination with metal ions has not been examined until recently. Such coordination may affect the results of biological experiments using bimanes, since metallic elements are common in biological systems.¹ In order to examine the interaction of metal ions with bimane, solutions containing syn-(Me,Me)bimane and Zn(II) or Co(II) salts were prepared. Changes in fluorescence, light absorption, and the bimane`s chemical structure were investigated. The solutions comprised solvents of different polarities, as well as varying concentrations of bimane and salts. To examine the molecular structure, a zinc-bimane complex was crystallized, and its structure was crystallographically characterized.
In this study, the fluorescence and absorbance decreased as the salt concentration increased, for most of the examined salts and solvents. Additionally, it was found that the effect of a given salt on the bimane`s fluorescence and absorbance decreased as the polarity of the solvent increased. When the influence of the bimane`s concentrations was tested it was found that in the lowest concentration, the decrease in light emission was the highest. Stern-Volmer analysis presented linear graphs, indicating that the fluorescence quenching is either static or dynamic, but not both. The crystal structure of the zinc complex revealed that the bimane`s backbone is bent, and that zinc binds to it through the two oxygen atoms. In general, the results show that the salts have a significant effect on the properties of the bimane, in terms of the fluorescence and absorption spectra, as well as the bimane`s chemical structure.

(1) P. J. Das, Y. Diskin-Posner, M. Montag, F. Grynszpan. Syn-Bimane as a chelating O-donor ligand for palladium. Dalton Trans. 2016, 45, 17123-17131.