Artificial photosynthetic systems for e.g. CO2 reduction rely on efficient electron transfer from photosensitizer to catalyst. Perylenediime (PDI) covalently bound to ReI(bpy)(CO)3 (Rebpy) is a prototype system, combining a strong photosensitizer/electron donor with a good catalyst for reductive chemistry. Treatment of the dyad with a mild chemical reductant produces the stable Rebpy–PDI−● radical anion which enhances the spectral coverage and the photoreductive strength of the PDI sensitizer. In this presentation, we will focus on the mechanism of spin-dependent ET resulting from selective excitation of the Rebpy part. Quantum chemical calculations, Marcus theory, and UV-vis transient absorption spectroscopy shows that photoinduced ET from PDI−● to 3*ReI-bpy forms two distinct charge-shifted states, depending on whether the two spin-polarized parts of 3*ReI-bpy–PDI−● are antiferro- or ferromagnetically coupled. Whereas the return to the ground state is spin-allowed in the former case, the latter persists for 67 ns due to spin-forbidden back-electron transfer, constituting a more than thousandfold lifetime enhancement. Exploiting this spin dependency holds promise for artificial photosynthetic systems requiring long-lived reduced states to perform multi-electron chemistry.

Spin-dependent photoinduced electron transfer in a prototype artificial-photosynthesis molecular framework

255th National Meeting (2018)

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