Multiphoton Processes and Directional Charge-Transfer in Ferrocene-Polyoxometalate Dyads and Triads

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Molecular metal oxides, so-called polyoxometalates (POMs) are versatile platform molecules for the design of multifunctional light-triggered reaction systems. POMs can act as platform molecules for the design of light-harvesting dyads as they are amenable for covalent functionalization with light-absorbing metal complexes, here ferrocene (Fc), as well as proton/electron donors. Ferrocene-POM dyads are ideal model systems as electronic coupling and charge-transfer between both components has recently been demonstrated by the applicants. In addition, the electronic structures and redox properties of ferrocene and POM can be adapted on the molecular level. Also, POMs can delocalize electrons across multiple metal centers, thereby offering ample opportunities for the design of dyads with long-lived charge-separated states. In addition, chemical modification of the ferrocene enables tuning of the (photo-)redox-properties and thus control light-absorption and charge transfer to the POM. Thus, these systems are of immense interest for the light-harvesting and energy conversion communities, and light-driven multi-electron charge-accumulation on POM dyads, as well as subsequent charge transfer, e.g. to photoelectrodes, has been demonstrated. Their roles in applications such as photovoltaics, photo-electrochemistry and light-driven water splitting are actively explored.In this proposal, we will study the fundamental photophysical and light-induced supramolecular properties of Fc-POM dyads and triads. Our specific focus is to rationalize the visible-light-induced formation and properties of charge-separated states and use time-resolved spectroscopic and spectro-electrochemical insights to direct component tuning efforts. This will lead to systems capable of directional (multiple) electron transfer from the peripheral groups to the POM. A specific advantage and challenge will be the coupling of electron and counter-cation (e.g. proton) transfer. We propose that this concept can reduce energetic electron-transfer barriers, resulting in efficient charge-separation, long charge-separated state lifetimes, and enable the study of multi-photon, multi-electron transfers in Fc-POM dyads and triads.