Photo-CIDNP Reveals Different Protonation Sites Depending on the Primary Step of the Photoinduced Electron-/Proton-Transfer Process with Ru(II) Polyazaaromatic Complexes

Troian-Gautier, Ludovic;Mugeniwabagara, Epiphanie;Fusaro, Luca;Cauët, Emilie;Luhmer, Michel;et.al.
(2017) Journal of the American chemical society — Vol. 139, n° 42, p. 14909-14912 (2017)

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  • Troian-Gautier, Ludovicorcid-logoUCLouvain
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  • Mugeniwabagara, Epiphanie
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  • Fusaro, Luca
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  • Cauët, Emilie
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  • Luhmer, Michelorcid-logo
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Abstract
The excited-state quenching of [Ru(TAP)2(HAT)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, HAT= 1,4,5,8,9,12-hexaazatriphenylene) by hydroquinone (H2Q), N-acetyl-tyrosine (N-Ac-Tyr) or guanosine-5′-monophosphate (GMP) was investigated at various pH values. The quenching occurs via electron/proton transfer, as evidenced by transient absorption spectroscopy and confirmed by 1H photochemically induced dynamic nuclear polarization (photo-CIDNP). Reductive quenching also occurs in strongly acidic solution despite a much shorter lifetime of the protonated excited-state complex. Photo-CIDNP revealed a different mechanism at low pH, involving protonation before electron transfer and yielding a distinct protonated monoreduced complex. The experimental photo-CIDNP patterns are consistent with density functional theory calculations. This work highlights the power of 1H photo-CIDNP for characterizing, at the atomic level, transient species involved in electron-transfer processes.
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Troian-Gautier, L., Mugeniwabagara, E., Fusaro, L., Cauët, E., Kirsch-De Mesmaeker, A., & Luhmer, M. (2017). Photo-CIDNP Reveals Different Protonation Sites Depending on the Primary Step of the Photoinduced Electron-/Proton-Transfer Process with Ru(II) Polyazaaromatic Complexes. Journal of the American chemical society, 139(42), 14909-14912. https://doi.org/10.1021/jacs.7b09513 (Original work published 2017)