Frankfurt 2006 – scientific programme
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MO: Molekülphysik
MO 21: Molecular Electronics and Energy Transfer
MO 21.6: Talk
Tuesday, March 14, 2006, 12:25–12:40, H12
Ultrafast Electronic Dynamics in Ordered Pentacene Films — •Tobias Bittkau1, Stefan Lochbrunner1, Ida Kozma1, Martin Huth2, Stefan Schiefer2, and Bert Nickel2 — 1Lehrstuhl für BioMolekulare Optik, LMU München — 2Department für Physik und CeNS, LMU München
Micro crystalline thin films of organic molecules are frequently used in organic electronics applications, especially for field effect transistors. In case of low defect densities such films can exhibit band transport. Pentacene films for example have a highly ordered, characteristic herring bone structure which seems to be responsible for the extraordinary high exciton mobility in these films. Since charge and energy transport properties are directly linked to the electronic structure and dynamics of the systems, we started investigating electronic excitations in ordered pentacene films with ultrafast absorption spectroscopy. Contrary to time resolved luminescence experiments, this technique allows also for the observation of non radiating species like polarons. We observe that the excitation induced bleach has a complex recovery kinetics consisting of a 400 fs, a 5 ps, and a some hundred ps component. The localization of the excitation and its dissociation into charged species is discussed with respect to spectral signatures appearing around 630 nm. In addition, we find an unexpected long lasting memory of the excitation polarization which points to highly anisotropic excitation exchange processes.