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"Variation of the ultrafast fluorescence quenching in 2,6-sulfanyl-core-substituted naphthalenediimides by electron transfer" Igor Pugliesi, Patrizia Krok, Stefan Lochbrunner, Alfred Blaszczyk, Carsten von Hänisch, Marcel Mayor, and Eberhard RiedleJ. Phys. Chem. A, 114, 12555-12560 (2010) Abstract: The ultrafast fluorescence quenching of 2,6-sulfanyl-core-substituted naphthalenediimides was investigated by transient spectroscopy. We find a strong dependence of the relaxation on the chemical structure of the substituent. Direct linking of an aryl rest to the sulfur atom leads to a strong red shift of the fluorescence in 1 ps and the disappearance of the emission in 5 to 7 ps depending on the polarity and viscosity of the solvent. This complex behavior is interpreted with the help of quantum chemical calculations. The calculations suggest that the initial relaxation corresponds to a planarization of the substituents and an associated partial electron transfer. This is followed by a twisting of the phenylsulfanyl substituents out of the molecular plane that allows a complete localization of the electron donating orbital on the aryl group. Finally the back transfer happens in another 5 to 7 ps. For an additional methylene spacer group between the sulfur and the aryl this sequence of relaxation steps is not possible and a simple exponential decay, slower by about one order of magnitude, is found. BMO authors (in alphabetic order): Patrizia Krok Stefan Lochbrunner Igor Pugliesi Eberhard Riedle  WWW-Version |