Fig. 3. (a) Excited-state lifetime of ATTO655 in D2O/H2O, ACN/H2O, or ACN/MeOH mixtures as a function of the volume fraction xv of H2O or MeOH. Dashed lines serve as guide to the eye to emphasize deviation of the curves from linearity. (b) Evolution of the fluorescence spectrum of ATTO655 in D2O upon addition of increasing amounts of H2O (at constant dye absorbance). The red curve corresponds to the fluorescence spectrum in pure D2O and the blue curve in pure H2O. (c) Excited-state lifetime of ATTO655 in various protonated (blue) and partially or fully deuterated (red) solvents. The two dashed lines indicate the lifetime levels observed in alcohols (lower) and in other non-alcoholic polar solvents (upper). (d) Solvent-assisted quenching rate constant ks determined for ATTO655 in the same solvents as in (c), with the assumption knr = 0 in acetonitrile-d3. (e) Excited-state lifetime of various fluorophores in H2O, 2-propanol, and HFIP. The similarity of the lifetime values in 2-propanol and HFIP indicates that the H-bond strength does not significantly influence the fluorescence quenching process. All error bars reflect uncertainties on the lifetime measurements.
