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MO: Fachverband Molekülphysik
MO 9: Femtosecond Spectroscopy 2
MO 9.4: Vortrag
Dienstag, 24. März 2015, 15:30–15:45, PH/HS1
Jumping and Diffusion of Excitons: Förster transfer drives annihilation in an organic system — •Franziska Fennel and Stefan Lochbrunner — Institut für Physik, Universitätsplatz 3, 18055 Rostock
In many organic materials absorption of light leads to the formation of mobile electronic excitations, i.e. Frenkel excitons. At high excitation densities they can interact with each other resulting in an accelerated decay of the exciton density due to exciton-exciton-annihilation. We investigate the underlying mechanisms and the subsequenty steps of annihilation in a disordered organic model system by ultrafast absorption spectroscopy. The time dependent exciton density can be discribed by two annihilation pathways, the direct energy transfer between two excited molecules and diffusive motion towards a second exciton preceding the annihilation event. It is found that both pathways can be quantitatively
understood by applying Förster energy transfer theory to describe the diffusion of the
excitons as well as the annihilation step itself. To this end previous formulations of
Förster theory are extended to account for the inhomogeneous distribution of the S0 - S1 transition
energies resulting in an effective diffusion constant. Our model system consists of dye molecules embedded in a PMMA matrix. This model system allows to tune the exciton diffusion constant via the chromophore concentration [1] and therefore one annihilation pathway can be emphasized with respect to the other.
F. Fennel, S. Lochbrunner, Phys. Chem. Chem. Phys. 13, 3527 (2011)