Hannover 2010 – scientific programme

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MO: Fachverband Molekülphysik

MO 21: Femtosecond Spectroscopy III

MO 21.4: Talk

Thursday, March 11, 2010, 14:45–15:00, F 102

One-Dimensional Excitation Migration in Perylene Bisimide Aggregates — •Henning Marciniak and Stefan Lochbrunner — Universität Rostock, Institut für Physik, Universitätsplatz 3, 18055 Rostock, Germany

Perylene bisimides are excellent dyes and versatile building blocks for supramolecular structures and organic n-type semiconductors. Only recently perylene bisimides became available which show the absorption characteristics of J-aggregates [1]. We apply steady state as well as femtosecond pump-probe absorption spectroscopy to J-aggregates of substituted perylene bisimides to investigate their excitonic properties. For the excitons a delocalization length of two monomers is derived from the narrowing of the absorption line shape due to aggregation. The transient measurements reveal signatures of excited state absorption which are slightly blue shifted from the ground state absorption and which can be assigned to one-exciton to two-exciton transitions. The decay dynamics of the transients shows a strong dependence on the excitation intensity. This points to exciton-exciton-annihilation and indicates that the excitons are mobile. Two models are considered in the analysis of the annihilation dynamics. In one case the exciton motion is described as a diffusive process and in the other case a single step Förster resonance energy transfer (FRET) from an exciton site to another exciton is assumed as rate determining process. Evidence is provided that the relevant motion occurs only along one dimension.

[1] X.-Q. Li, X. Zhang, S. Ghosh, and F. Würthner, Chem. Eur. J. 14 (2008), 8074.