Cd. Clark et Mz. Hoffman, DOES BACK ELECTRON-TRANSFER WITHIN GEMINATE REDOX PAIRS FORMED IN BIMOLECULAR QUENCHING FOLLOW A MARCUS BELL-SHAPED ENERGY-GAP DEPENDENCE, Journal of photochemistry and photobiology. A, Chemistry, 99(1), 1996, pp. 9-11
The temperature dependence of the cage escape yield (eta(ce)) of redox
products from the quenching of Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine
) by aromatic amines in deaerated 1:1 (nu/nu) CH3CN/H2O solutions has
been examined. Values of lambda, the solvent reorganization energy upo
n electron transfer within the geminate redox pairs, have been extract
ed from plots of log((eta(ce)(-1)-1)T-1/2) vs. 1/T; the more stericall
y hindered two-ring amines exhibit a higher value of lambda (1.1 +/- 0
.08 eV) than do most of the one-ring amines (0.82 +/- 0.04 eV). A Marc
us plot of log(eta(ce)(-1)-1) vs. Delta G(bt)(0) shows a correlation w
ithin only the inverted region for systems with the same lambda; the e
arlier identification of the results for the same photosensitizer and
quenchers as a bell-shaped energy-gap curve is due to the coincidental
overlap of two independent segments within the inverted region.