@Article{JPhysChemA_108_549, author = {S. Pag{\`e}s and B. Lang and E. Vauthey}, title = {{Ultrafast Spectroscopic Investigation of the Charge Recombination Dynamics of Ion Pairs Formed upon Highly Exergonic Bimolecular Electron-Transfer Quenching: Looking for the Normal Region}}, journal= {J. Phys. Chem. A}, ISSN = {1089-5639}, volume= {108}, number= {4}, pages = {549-555}, url = {http://pubs.acs.org/cgi-bin/abstract.cgi/jpcafh/2004/108/i04/abs/jp036796g.html}, doi= {10.1021/jp036796g}, 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 ($\Delta${\em G}$_{CS}$= -2.2 eV), but charge recombination is weakly exergonic ($\Delta${\em G}$_{CR}$ = -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).}}, year = {2004} }