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Ultrafast Spectroscopic Investigation of the Charge Recombination Dynamics of Ion Pairs Formed upon Highly Exergonic Bimolecular Electron-Transfer Quenching: Looking for the Normal Region

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Published in Journal of Physical Chemistry. A. 2004, vol. 108, no. 4, p. 549-555
Abstract The charge recombination dynamics of the ion pairs formed upon electron-transfer quenching of perylene by tetracyanoethylene in acetonitrile has been investigated using ultrafast fluorescence upconversion, transient absorption, and transient grating techniques. For this donor/acceptor pair, charge separation is highly exergonic (ΔG[CS]= −2.2 eV), but charge recombination is weakly exergonic (ΔG[CR] = −0.6 eV). It was found that for more than 90% of the ion pair population, charge recombination is ultrafast and occurs in less than 10 ps. This decay component could not be observed in a previous investigation with a lower time resolution. The results indicate that the primary quenching product is a contact ion pair and not a solvent-separated ion pair as generally assumed for highly exergonic electron-transfer quenching processes. A possible explanation for this apparent divergence is that the contact ion pair is initially formed in an electronic excited state. Only a very minor fraction of the ion pair population undergoes the slow charge recombination predicted by Marcus theory for weakly exergonic charge-transfer processes (normal region).
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Research group Groupe Vauthey
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PAGES, Stéphane, LANG, Bernhard Felix, VAUTHEY, Eric. Ultrafast Spectroscopic Investigation of the Charge Recombination Dynamics of Ion Pairs Formed upon Highly Exergonic Bimolecular Electron-Transfer Quenching: Looking for the Normal Region. In: Journal of Physical Chemistry. A, 2004, vol. 108, n° 4, p. 549-555. doi: 10.1021/jp036796g https://archive-ouverte.unige.ch/unige:3517

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Deposited on : 2009-10-02

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