Fluorescence Quenching of Auramine in Fluid Solutions: A Femtosecond Spectroscopy Study |
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Authors: | P Changenet H Zhang M J van der Meer M Glasbeek P Plaza M M Martin |
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Institution: | (1) Laboratory for Physical Chemistry, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands;(2) Laboratoire de Photophysique Moléculaire du CNRS (UPR 3361), Université Paris-Sud, Bât. 210, 91405 Orsay Cedex, France;(3) Laboratoire de Photophysique Moléculaire du CNRS (UPR 3361), Université Paris-Sud, Bât. 210, 91405 Orsay Cedex, France |
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Abstract: | The quenching of Auramine fluorescence in ethanol is studied by two ultrafast spectroscopy techniques. The gain band, probed by transient absorption spectroscopy, vanishes in a few picoseconds, while a transient absorption band rises and the ground-state repopulation is delayed. In up-conversion experiments, nonexponential wavelength-dependent fluorescence decays are observed. The average decay times increase with the wavelength and the reconstructed instantaneous spectrum exhibits a few hundred-wavenumber red shift and a broadening while its intensity drops. The previously proposed relaxation model, involving a barrierless internal twisting motion toward a transient dark state, is further examined. In particular, the extinction coefficients of the transient state are extracted from the differential absorption spectra. The band is found to lie in the same wavelength range as the dimethylaniline cation radical. This result is discussed as a possible support for an internal twisting process involving a charge shift. |
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Keywords: | Fluorescent probe ultrafast spectroscopy barrierless twisting charge shift |
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