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MO: Molekülphysik
MO 1: Elektronische Übergänge
MO 1.2: Talk
Monday, March 4, 2002, 14:15–14:30, HS 01/E01
Orientation of Excited State Transition Dipoles in Tetrapyrroles with Different Molecular Symmetry — •Jörg Zimmermann1, Hendrik Fuchs2, Andre Zeug2 und Beate Röder2 — 1University of California, Berkeley, Department of Chemistry — 2Humboldt Universität Berlin, Institut für Physik
The knowledge of the orientation of electronic transition dipole moments within the molecular frame is of practical interest e.g. for optical limiting or intermolecular energy transfer. So far, the orientations of transition dipole moments in tetrapyrroles have been investigated mainly by fluorescence anisotropy that allows determination of the orientations of S0-Sn absorption transition dipoles in respect to a fixed emission transition dipole. However, little is known about the orientation of excited state absorption (ESA) transition dipoles. Transient absorption spectroscopy (TAS) with polarized probing permits access to these transitions. We present photoinduced fluorescence and TAS anisotropy data of three tetrapyrroles of different molecular symmetry. The orientation of the S0-Sn and S1-Sn transition dipoles were extracted from these data. A distinctive influence of the molecular symmetry was found for tetra(t-butyl)-phthalocyanine and its Zinc complex due to a doubly degenerated S1 state in the latter. For a Chlorophyll like molecule, Pheophorbide-a, the asymmetric substituents influence the orientation of the electronic transition only slightly.