%0 Journal Article %A Muller, P.-A. %A Vauthey, E. %T Charge Recombination Dynamics of Geminate Ion Pairs Formed by Electron Transfer Quenching of Molecules in an Upper Excited State %J Journal of Physical Chemistry A %@ 1089-5639 %V 105 %N 25 %P 5994-6000 %D 2001 %U http://pubs.acs.org/doi/abs/10.1021/jp010015z %R 10.1021/jp010015z %U http://archive-ouverte.unige.ch/unige:3338 %X An investigation of the charge recombination (CR) dynamics of geminate ion pairs formed upon electron transfer quenching of azulene, benz[a]azulene, and xanthione in the second singlet excited state by several electron donors, using ultrafast time resolved spectroscopy and photoconductivity is reported. The ion pairs have two possible CR pathways:Â (i) a highly exergonic CR to the neutral ground state or (ii) a moderately exergonic CR leading to the formation of the neutral acceptor in the first singlet excited state. This investigation shows strong evidence of the predominance of the second pathway. CR in ion pairs formed with the azulenes is faster by a factor of more than 50 than in ion pairs having a similar energy but with the first CR pathway only. The electron transfer quenching of xanthione in the second singlet excited state by several weak donors does not lead to a significant reduction of the triplet yield of this molecule. The relevance of these results to explain the absence of the inverted region in highly exergonic bimolecular charge separation reactions is discussed.