Modulation of intramolecular Fe oxidation with distance and driving force in Ru–Fe photocatalysts

Abstract

In this paper we have investigated the efficiency of the intramolecular electron transfer process in a family of Ru^II–Fe^II dyads, previously shown to perform the light-driven activation of an iron-bound water molecule. The Ru chromophore and Fe catalytic units are connected at different lengths through a triazole group attached to an alkyl chain containing either three or five carbon atoms. The driving force for Fe oxidation is modified by adding ethyl ester substituents on the bipyridines completing the coordination sphere of a [Ru(bpy)₃]²⁺-like chromophore. Transient absorption measurements and simulations were used to obtain the rate constants of internal charge transfer for the different complexes. The parameters governing the electron transfer process, reorganisation energy λ and electronic coupling H_AB were obtained, and the observed variations are discussed within the framework of Marcus theory, which can help in understanding how to optimize the design of molecular photocatalysts.