Hannover 2013 – scientific programme

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MO: Fachverband Molekülphysik

MO 23: Femtosecond Spectroscopy VI

MO 23.1: Invited Talk

Thursday, March 21, 2013, 14:00–14:30, F 102

Ultrafast Dynamics of Electronic Excitations in Organic Materials and Structures — •Stefan Lochbrunner, Henning Marciniak, Franziska Fennel, and Steffen Wolter — University of Rostock, 18051 Rostock

In future, supramolecular organic structures will be most probably employed in a wide range of photonic devices like organic solar cells and light emitting diodes. Therefore, the behavior of their fundamental electronic excitations, so-called Frenkel excitons, is subject of intense research activities. One key element is the diffusion of excitons which depends sensitively on the degree of order in the organic material. Our femtosecond pump-probe experiments on different systems show that it is possible to discriminate between different relaxation scenarios and to provide absolute numbers for local mobilities.

In a disordered organic material energetic down hill migration within the inhomogeneous distribution of site energies resulting in a low exciton mobility is observed and simulated by Förster transfer processes [1]. In J-aggregates the degree of order is much higher and the excitons are highly mobile throughout their lifetime. Modeling of the observed exciton-exciton annihilation dynamics reveals that the mobility is in this case strictly one dimensional. Contrary, in microcrystalline pentacene three dimensional diffusion is found and traps restrict the mobility of the excitons [2].

[1] F. Fennel and S. Lochbrunner, Phys. Rev. B 85 (2012), 094203.

[2] H. Marciniak, I. Pugliesi, B. Nickel, and S. Lochbrunner, Phys. Rev. B 79 (2009), 235318.