Supramolecular Control of Photoinduced Electron Transfer between Tungsten Halide Clusters and Polyoxometalates in Water

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Abstract
Identifying systems composed of earth-abundant elements capable of photoinduced electron-transfer represents a major breakthrough for the development of sustainable photocatalytic processes. Herein, we demonstrate that octahedral tungsten-halide clusters constitute a promising new class of robust photosensitizers, owing to their exceptional chemical stability, intense luminescence, and long-lived triplet excited states. Upon irradiation in aqueous solution, these species transfer an electron to polyoxometalates (POMs), well-known molecular catalysts capable of multielectron redox chemistry. More specifically, we investigate the photophysical properties of supramolecular systems combining the cluster-based motif [{W6Ii8}Cla6]2– and a series of archetypal POMs ([PW12O40]3–, [SiW12O40]4–, [BW12O40]5–, [P2W18O62]6–) as electron-acceptor units, in the presence of γ-cyclodextrin (γ-CD), which acts as both a supramolecular assembly scaffold and a stabilizing agent. The photoinduced electron-transfer process was investigated using steady-state and time-resolved optical spectroscopy, complemented by spectro-electrochemical measurements, which unambiguously confirm electron transfer from the excited cluster to the POMs. Furthermore, we demonstrate that both the ionic charge of the POMs and the presence of γ-CD significantly influence the efficiency of the process. This work highlights the dual role of γ-CD, which facilitates the association of two negatively charged inorganic units and stabilizes the charge-separated state by maintaining an appropriate spatial arrangement within the supramolecular assembly.
Funding Information
  • Agence Nationale de la Recherche (ANR-22-CE50-0007-01)

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