Düsseldorf 2007 – scientific programme
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MO: Fachverband Molekülphysik
MO 52: Femtosecond Spectroscopy IV
MO 52.6: Talk
Thursday, March 22, 2007, 15:15–15:30, 6B
Ultrafast Excimer Formation in Perylene Bisimide Aggregates — Stefan Schindlbeck1, •Stefan Lochbrunner1, Volker Dehm2, and Frank Würthner2 — 1Lehrstuhl für BioMolekulare Optik, LMU München — 2Institut für Organische Chemie, Universität Würzburg
Perylene bisimide dyes are versatile building blocks in organic electronics and their aggregates represent promising functional units. 1-dimensional aggregates are generated by self-assembly of tridodecylphenyl substituted perylene bisimide molecules [1]. We investigate the electronic structure of these aggregates with femtosecond absorption spectroscopy to provide the underlying knowledge for understanding the behavior of corresponding functional units. The transient spectrum observed after optical excitation into the first electronic absorption band consists of ground state bleach and a broad and structureless excited state absorption. No indications for a reasonable strong stimulated emission are found even at short delay times down to 100 fs. This is surprising since the absorption is associated with a strong transition dipole and points to an extremely fast change in the electronic wavefunction that reduces efficiently the oscillator strength. The results are explained by the formation of excimers and a reduction of the intermolecular distance. The electronic wavefunction exhibits charge transfer character in the potential minimum whereas the S1 character of the monomer dominates in the Franck-Condon region.
[1] F. Würthner, Z. Chen, V. Dehm, and V. Stepanenko, Chem. Commun. 2006, 1188.