Counterion Exchange Enhances the Brightness and Photostability of a Fluorous Cyanine Dye

Fluorofluorophores are a unique class of fluorophores that can be solubilized in perfluorocarbons (PFCs) and used to study biological systems. However, because of the low dielectric constant and high oxygen solubility in the fluorous phase, the brightness and photostability of the fluorofluorophores are significantly diminished. Here, we leveraged the tight ion pairing in the fluorous phase to improve the photophysical properties of a fluorous soluble pentamethine dye (FCy5) via counterion exchange. We found that larger, softer, fluorinated, aryl borate counterions promote the ideal polymethine state where charge delocalization across the polymethine chain increases the brightness (6-fold) and photostability (55-fold) of FCy5.