Düsseldorf 2007 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 52: Femtosecond Spectroscopy IV
MO 52.1: Vortrag
Donnerstag, 22. März 2007, 14:00–14:15, 6B
Ultrafast Fluorescence Quenching in a Naphthalene Bisimide Dye — Patrizia Krok1, •Stefan Lochbrunner1, Alfred Błaszczyk2, Marcel Mayor2, and Eberhard Riedle1 — 1Lehrstuhl für BioMolekulare Optik, LMU München — 2Department für Chemie, Universität Basel
Naphthalen bisimide dyes are promising candidates for molecular electronics applications since their electronic structure can be efficiently tuned by substituents. In the case of two phenyl substituted naphthalene bisimide derivatives we find that the fluorescence quantum yield [1] and the emission lifetime of the naphthalene chromophore depend strongly on the number of carbon atoms in the linker between the chromophore and the phenyl substituent. While a benzyl thio substituted derivative emits reasonably strong fluorescence from the S1 state, the fluorescence of a phenyl thio substituted derivative is reduced by a factor of 16. In a pump-probe experiment the transient absorption of both molecules was studied after selective excitation into the S1, S2, or the S3 state. The experimental traces reveal an ultrafast nonradiative decay of the higher states into S1. The lifetime of the stimulated emission from the S1 state is 40 ps for the fluorescent dye and only 6 ps for the nonfluorescent dye. We argue that the fast decay is the result of an electron transfer from the phenyl substituent to the chromophore. The charge transfer state has a similar lifetime of also about 6 ps, which we understand as the time for the charge recombination.
[1] A. Błaszczyk, M. Fischer, C. von Hänisch, and M. Mayor, Helvetica Chimica Acta 89 (2006), 1986.