Real-time probing of solvent caging effects during IR electron transfers in solution
Résumé
We investigate the real-time probing of nonequilibrium electron transfers in aqueous solutions of disulfide molecules. Our attention is focused on the elementary steps of an IR electron transfer from a charged donor (chloride ion) to a biomolecular acceptor (cystamine dihydrochloride: RSSR, 2HCl, R = (CH2)2 NH2). Following a femtosecond UV excitation of the ionic donor, an ultrafast electron attachment on a SS bond takes place with a time constant of 160 ′ 20 fs at 294K. The determination of a UV signature centered around 3.0 eV and characterized by a half band width of 0.6 eV substantiates the subpicosecond formation of a nascent sulfur-centered radical anion (RS SR-) with a 2σ/1σ* bond. The ultrafast attachment of an IR prehydrated electron on a S-S bond competes with the nonadiabatic radiationless transition of IR p-like electrons. These results raise the fundamental importance of solvent caging effects during the efficient coupling between a p-like IR prehydrated electron and a S-S bond.