Ultrafast photochemical dynamics of the hexaaquairon(III) ion

Abstract

UV excitation of [Fe(H2O)6]3+ generates hydroxyl radicals in low quantum yield, but the events that compete with this photochemistry are obscure. To elucidate the primary events, acidic, aqueous iron(III) perchlorate solutions were studied by femtosecond pump-probe spectroscopy. We report a new decay channel in which ligand-to-metal charge transfer (LMCT) excitation of [Fe(H2O)6]3+ hydrolyzes a coordinated water molecule, releasing a proton and forming the iron(III) monohydroxy ion in less than 1ps. This efficient channel, which is observed here for the first time, competes with hydroxyl radical generation and represents a novel observation of photoacidity in a metal coordination complex.