This blue-red cross-talk occurs because the red Bodipy displays a significant absorbance in the 400 -450 nm region. The only visible spectral region in which the red Bodipy displays only weak absorbance is between 480 -530 nm but irradiation in this spectral region leads to some direct excitation of the green fluorophore, A solution of 22•dbu (c= 5.0 • 10 -6 mol/L) was treated with one equivalent of [AuCl(NHC_red)] and irradiated at 423 nm (fig. ). This leads to an instantaneous increase of the red emission, 74 but it does not produce a significant change in the green emission. Obviously, the 423 nm light leads to the excitation of the blue Bodipy and the excitation energy is then transferred to the green dye via FRET.