The first corollary is a wavelength-dependent difference in the heavy water florescence enhancement effect. That is, ICG should exhibit a larger heavy water florescence enhancement effect because there is increased spectral overlap of its 805 nm fluorescence emission band with the 700-900 nm H2O absorption band, a trend that is evident in the data sets produced by previous studies. In Figure is a collection of fluorescence spectra and imaging data for equimolar solutions of ICG and ICB in H2O and D2O. In Figure are the normalized emission spectra for ICB and ICG, and the absorption spectrum of water. There is more spectral overlap of water with ICG than ICB as judged by the area-under-the-curve ratios of 0.27 for H2O/ICG and 0.18 for H2O/ICB. The fluorescence emission spectra in Figure confirm the prediction that the larger spectral overlap with ICG leads to a greater D2O enhancement effect. That is, the ratio of integrated fluorescence intensities (I.F.D2O/I.F.H2O) for ICG (2.94) is substantially larger than the corresponding ratio for ICB (1.63). This trend was also apparent in fluorescence imaging experiments that used an in vivo imaging station to image microwell plates containing the different solutions of ICB and ICG (Figure ). That is, the ratio of mean pixel intensity (MPI) values for the different images (MIPD2O/MIPH2O) was 2.94 for ICG and 1.56 for ICB. Finally, we confirmed that dye excited state lifetime was relatively longer in D2O than in H2O as expected for a FRETbased quenching mechanism (Figure ).