Concerted proton-electron transfer reactions in the Marcus inverted region

Protons venture into the inverted region One of the most counterintuitive features of electron transfer kinetics is the inverted region. As Marcus theory predicts and experiments have borne out, electron transfer slows down once the driving force for it becomes especially favorable. Parada et al. now offer evidence for such inverted behavior in proton-coupled electron transfer (see the Perspective by Dempsey). Specifically, they examined a series of compounds with phenol bridging anthracene (electron acceptor) and pyridine (proton acceptor) derivatives. Time-resolved spectroscopy and accompanying theory revealed slower rates at higher driving forces in the back reaction that follows light-induced intramolecular proton and electron transfer. Science , this issue p. 471 ; see also p. 436