PHYS 359 |
| The Photophysics of 4-dimethylamino-4'-cyanostilbene (DCS) has been under discussion for many years. The main question still to be resolved is whether dual fluorescence occurs for this compound and if yes what the underlying intramolecular mechanism is. Dual fluorescence in different donor-acceptor-substituted stilbene derivatives was proposed by Pines et al on the basis of fluorescence spectra reconstructed from single kinetics with 20 ps cross-correlation. On the contrary, no indication of dual fluorescence has been found by Kovalenko et al who examined DCS with femtosecond broadband transient absorption and fluorescence upconversion spectroscopies. It was concluded that an isoemissive point in the time-resolved fluorescence results from spectral overlap with strong excited-state absorption. At low optical density and pump fluence, the isoemissive point disappears and only solvation dynamics remains. We report on Kerr-shutter broadband transient fluorescence of DCS with 0.6 ps cross-correlation time and ~ 20 000 cm-1 spectral coverage. This setup is similar to that demonstrated by Maroncelli et al but with improved background suppression. The technique is significantly better in time resolution than Pine's photon-counting experiment. In addition, broadband conditions together with quasi-flat spectral efficiency yields better photometric accuracy in comparison with the fluorescence up-conversion technique. Our results show excellent agreement with those of Kovalenko et al Dual fluorescence can not be corroborated. |
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Physical Chemistry Poster Session
7:00 PM-9:00 PM, Wednesday, August 22, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Physical Chemistry |