Isotope Effect in the Time Resolved Fluorescence of Anthracene in Small Unilamellar Vesicles

Abstract

The fluorescence decay of anthracene in small unilamellar vesicles (SUV) was determined employing a precise single photon counting technique. The fluorescence data were fitted best by a biexponential decay law. The longer component τ2 (4.75 ns at 26.0 °C) represents the decay time of anthracene being quenched by the lipid molecules. The shorter (red shifted) component τ1 (1.47 ns at 26.0 °C) displays a strong solvent (H2O/D2O) isotope effect. Therefore it is suggested that a number of H2O molecules may be present in the interior of the lipid bilayer. Both τ1 and τ2 processes display an apparent negative activation energy below the main phase transition which may be explained by a pre‐equilibrium whose ΔH0 is more negative than the positive activation energy of the subsequent emission step.