The fluorescence emission of a naphthalene unit attached to a polyamine chain is quenched by intramolecularelectron transfer from the deprotonated amines to the excited fluorophore. Measurements of the respectivequenching rate constants as a function of the distance, reveal an exponential dependence with β = 0.45 Å-1.Identical measurements carried out in deuterated water have shown a similar dependence with the distanceβ = 0.49 Å-1 but an average reduction of the absolute values of the rate constants of ca. 1.2. The polyaminechains seem to constitute a bridge through which the electron can find a route to its movement, more efficientlythan through space.