Design of an antenna system for the collection of singlet excitation energy. Exciton diffusion among concentrated 9,10-diphenylanthracene centers in polystyrene

Fluorescence decay kinetics of 9,10-diphenylanthracene (DPA) were examined at (DPA) = 16 to 181 mM in spin-cast polystyrene films of approx. 2000-A thickness. Exponential decays with lifetimes ranging from 6.94 ns at low concentration to 6.34 ns at 180 mM were observed in unquenched systems. In the presence of tetrabromo-o-benzoquinone (TBBQ), added at 12.0 mM as a quenching probe, the decay kinetics were modified. At very low concentrations of DPA, nearly pure Foerster kinetics were observed. Extrapolation of behavior to (DPA) = 0 gave a critical transfer radius for Foerster transfer from DPA to TBBQ of 28 A. Calculations from spectral data gave 29 A. As the concentration of DPA increased, quenching became progressively more efficient and the time dependence of decay showed evidence of excitation diffusion by hopping from DPA site to DPA site. Diffusion coefficients were evaluated by two-parameter fits of decays to curves predicted from the Yokota-Tanimoto theory based on a Pade approximant. Values of the diffusion coefficient increased with (DPA) to 7.9 x 10/sup -6/ cm/sup 2//s at (DPA) = 180 mM. The corresponding diffusion length is 55 A. The meaning of the results to the construction of an antenna system for collection of photonic energymore » into photochemical reaction centers is discussed.« less