TY - JOUR
AU - Vauthey, E.
TI - Direct Measurements of the Charge-Recombination Dynamics of Geminate Ion Pairs Formed upon Electron-Transfer Quenching at High Donor Concentration
PY - 2001
JF - Journal of Physical Chemistry A
JA - J. Phys. Chem. A
SN - 1089-5639
VL - 105
IS - 2
SP - 340
EP - 348
L1 - http://pubs.acs.org/doi/pdf/10.1021/jp0023260
L2 - http://pubs.acs.org/doi/full/10.1021/jp0023260
L3 - http://pubs.acs.org/doi/abs/10.1021/jp0023260
M3 - 10.1021/jp0023260
UR - http://dx.doi.org/10.1021/jp0023260
N2 - The rate constants of back-electron-transfer (BET) reaction within geminate ion pairs generated upon static ET quenching of cyano-substituted anthracenes by aromatic amines and methoxy-substituted benzenes (MSB) at high concentration in acetonitrile have been measured directly using ultrafast multiplex transient grating spectroscopy. The free energy of BET, ΔGBET, was varied between −3.0 and −0.6 eV, a range corresponding, in principle, to the inverted, barrierless, and normal regimes. When plotted vs ΔGBET, the measured rate constants, kBET, exhibit a large scattering. Good fits of the semiclassical expression for nonadiabatic ET are obtained if the rate constants are sorted according to the electron donor. The resulting electronic coupling matrix elements V are larger and the solvent reorganization energies smaller than those reported for BET within solvent-separated ion pairs, suggesting that BET takes place between ions in contact. However, in the low exergonicity region, the observed BET rate constants are slower than those reported for contact ion pairs formed by charge-transfer excitation. The dynamics of BET within radical pairs generated upon ET quenching of the N-methylacridinium cation has also been investigated, and the role of the electrostatic interaction within geminate ion pairs is discussed.
ID - 88
ER -

TY - JOUR
AU - Muller, P.-A.
AU - Vauthey, E.
TI - Charge Recombination Dynamics of Geminate Ion Pairs Formed by Electron Transfer Quenching of Molecules in an Upper Excited State
PY - 2001
JF - Journal of Physical Chemistry A
JA - J. Phys. Chem. A
SN - 1089-5639
VL - 105
IS - 25
SP - 5994
EP - 6000
L1 - http://pubs.acs.org/doi/pdf/10.1021/jp010015z
L2 - http://pubs.acs.org/doi/full/10.1021/jp010015z
L3 - http://pubs.acs.org/doi/abs/10.1021/jp010015z
M3 - 10.1021/jp010015z
UR - http://dx.doi.org/10.1021/jp010015z
N2 - 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:  (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.
ID - 87
ER -

TY - JOUR
AU - Brodard, Pierre
AU - Sarbach, Alexandre
AU - Gumy, Jean-Claude
AU - Bally, Thomas
AU - Vauthey, Eric
TI - Excited-State Dynamics of Organic Radical Ions in Liquids and in Low-Temperature Matrices
PY - 2001
JF - Journal of Physical Chemistry A
JA - J. Phys. Chem. A
SN - 1089-5639
VL - 105
IS - 27
SP - 6594
EP - 6601
L1 - http://pubs.acs.org/doi/pdf/10.1021/jp010808l
L2 - http://pubs.acs.org/doi/full/10.1021/jp010808l
L3 - http://pubs.acs.org/doi/abs/10.1021/jp010808l
M3 - 10.1021/jp010808l
UR - http://dx.doi.org/10.1021/jp010808l
N2 - The excited-state dynamics of the radical cations of perylene (PE•+), tetracene (TE•+), and thianthrene (TH•+), as well as the radical anions of anthraquinone (AQ•-) and tetracenequinone (TQ•-), formed by γ irradiation in low-temperature matrices (PE•+, TH•+, AQ•-, and TQ•-) or by oxidation in sulfuric acid (PE•+, TE•+, and TH•+) have been investigated using ultrafast pump−probe spectroscopy. The longest ground-state recovery time measured was 100 ps. The excited-state lifetime of PE•+ is substantially longer in low-temperature matrices than in H2SO4, where the effects of perdeuteration and of temperature on the ground-state recovery dynamics indicate that internal conversion is not the major decay channel of PE•+*. The data suggest that both PE•+* and TE•+* decay mainly through an intermolecular quenching process, most probably a reversible charge transfer reaction. Contrarily to AQ•-*, TQ•-* exhibits an emission in the visible which, according to theoretical calculations, occurs from an upper excited state.
ID - 86
ER -