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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

Published inThe journal of physical chemistry. A, vol. 108, no. 4, p. 549-555
Publication date2004
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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Citation (ISO format)
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: The journal of physical chemistry. A, 2004, vol. 108, n° 4, p. 549–555. doi: 10.1021/jp036796g
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ISSN of the journal1089-5639
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