Hannover 2013 – scientific programme

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MO: Fachverband Molekülphysik

MO 23: Femtosecond Spectroscopy VI

MO 23.3: Talk

Thursday, March 21, 2013, 14:45–15:00, F 102

Low Temperature Exciton Dynamics in Perylene Bisimide Aggregates — Steffen Wolter, •Franziska Fennel, Karl Magnus Westphal, and Stefan Lochbrunner — Universität Rostock, Institut für Physik, Universitätsplatz 3, 18055 Rostock

In this contribution a perylene bisimide dye is investigated which assembles into one-dimensional J-aggregates at ambient conditions. It is a promising candidate for photonic applications due to its high quantum yield and exciton mobility. In first temperature dependent experiments, we were able to switch between H-type and J-type aggregates by varying the aggregate length and found, that only in the latter case diffusion driven exciton-exciton annihilation occurs [1]. Our studies focus now on the exciton dynamics at low temperatures to characterize the influence of dynamic and static disorder.

We present stationary and femtosecond pump-probe spectra down to liquid nitrogen temperature using a continuous flow cryostat. They indicate that at low temperatures a certain amount of static disorder remains and prevents the exciton wavefunction from spreading over more than a few molecules. However, the excitons stay mobile and exciton-exciton-annihilation again happens to be a prominent decay mechanism. The mobility seems to be governed by a delicate interplay between static disorder and thermal fluctuations. The exciton diffusion properties at room temperature and at 77 K are compared with respect to the delocalization length, diffusion constant and static disorder.

[1] Wolter S., Aizezers J., Fennel F., Seidel M., Würthner F., Kühn O., Lochbrunner S. New J. Phys. 14, 105027 (2012)