Bodipysulfonate anion was synthesized in the reaction of [AuCl(NHC_red)] with the silver salt of Bodipysulfonate (scheme 5). A solution of complex 18 in toluene displays a strong FRET signal, indicating the presence of close ion pairs in the weakly solvating aromatic solvent (excitation spectra red and green circles, fig. ). The close ion pairs can be separated by addition of a polar solvent, such as DMAc (excitation spectra red and green triangles, fig. ). The increase in the dielectric constant of the solvent mixture and the weak interaction of DMAc with gold lead to solvent-separated ion pairs, which are characterized by a weak 648 nm signal (red triangles, fig. ) and a strong 535 nm signal upon excitation at 500 nm.