Photochemistry of iron(iii)-lactic acid complex in aqueous solutions

Abstract

Photochemistry of a 1: 1 FeIII-lactic acid complex, [Fe(Lact)]+, in aqueous solutions was studied by stationary photolysis, nanosecond laser flash photolysis (355 nm, 6 ns), and femtosecond pump-probe spectroscopy (400 nm, 200 fs). The quantum yield of photolysis of [Fe(Lact)]+ upon excitation at 355 nm is 0.4 and 0.22 in the deoxygenated and air-saturated solutions, respectively. Weak transient absorption in the range 500–750 nm was observed in the nanosecond experiments. It was assigned to a [FeII...-O-CH(Me)-COO·]+ radical complex. The spectral properties of the ligand-to-metal charge transfer excited state and the characteristic time of formation of the radical complex (1.5 ps) were determined in the femtosecond spectroscopy experiments. A reaction mechanism was proposed, which involves inner-sphere electron transfer in the excited complex with the formation of a radical complex [FeII...-O-CH(Me)-COO·]+ and its subsequent transformation to the end product of the photochemical reaction.