Energy transfer in organic systems VII. Effect of diffusion on fluorescence decay

The effect of non-radiative energy transfer and diffusion on the fluorescence decay of phenanthrene in the presence of acridine was observed in six solvents of viscosity η = 0.4 cp to 64.6 cp. The system obeys Stern-Volmer kinetics at low η, Förster kinetics at high η and intermediate kinetics at medium η. At η = 64.6 cp the decay obeys the Förster relation. At lower η it agrees satisfactorily with the relation of Yokota and Tanimoto, but it is less rapid than that predicted by Voltz et al.