Frankfurt 2006 – scientific programme

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MO: Molekülphysik

MO 21: Molecular Electronics and Energy Transfer

MO 21.5: Talk

Tuesday, March 14, 2006, 12:10–12:25, H12

Towards Dispersion Free Exciton Diffusion: Ultrafast Förster Transfer in Doped Polymer Films — •Stefan Lochbrunner and Martin Schlosser — LS für BioMolekulare Optik, Ludwig-Maximilians-Universität München

In optoelectronic applications of organic thin film systems the absorbed energy is transported by exciton diffusion to the active interface where charge separation occurs. In unordered materials like in most polymers the sites exhibit electronic states with a large energy dispersion and the excitons are trapped at low energy sites. Therefore we propose as active sites chromophores which are incorporated in the polymer matrix but interact only weakly with the polymeric environment. Their electronic states have similar energies and no trapping of the excitons should occur allowing for a dispersion and loss free long range energy transport by Förster transfer between them. To test the approach we performed femtosecond absorption experiments on PMMA films highly doped with perylene bisimide dyes and characterized the energy transfer between the chromophores. We find a stretched exponential time dependence characteristic for Förster energy transfer between immobilized chromophores with a transfer time of 1.5 ps for an average distance of 2.3 nm resulting in a high mobility of the optically generated excitons. We can also collect the energy with high efficiency on dye molecules which exhibit an absorption spectrum that is red shifted compared to the perylene dyes responsible for the exciton diffusion. This opens a design route for artificial light harvesting complexes.