Counterion Effects in [Ru(bpy)<sub>3</sub>](X)<sub>2</sub>-Photocatalyzed Energy Transfer Reactions - Archive ouverte HAL
Article Dans Une Revue JACS Au Année : 2024

Counterion Effects in [Ru(bpy)3](X)2-Photocatalyzed Energy Transfer Reactions

Carine Duhayon
Christophe Coudret
Yves Canac
Olivier Baslé

Résumé

Photocatalysis that uses the energy of light to promote chemical transformations by exploiting the reactivity of excited-state molecules is at the heart of a virtuous dynamic within the chemical community. Visible-light metal-based photosensitizers are most prominent in organic synthesis, thanks to their versatile ligand structure tunability allowing to adjust photocatalytic properties toward specific applications. Nevertheless, a large majority of these photocatalysts are cationic species whose counterion effects remain underestimated and overlooked. In this report, we show that modification of the X counterions constitutive of [Ru(bpy)3](X)2 photocatalysts modulates their catalytic activities in intermolecular [2 + 2] cycloaddition reactions operating through triplet–triplet energy transfer (TTEnT). Particularly noteworthy is the dramatic impact observed in low-dielectric constant solvent over the excited-state quenching coefficient, which varies by two orders of magnitude depending on whether X is a large weakly bound (BAr$^F$4$^–$) or a tightly bound (TsO$^–$) anion. In addition, the counterion identity also greatly affects the photophysical properties of the cationic ruthenium complex, with [Ru(bpy)3](BAr$^F$4)2 exhibiting the shortest 3MLCT excited-state lifetime, highest excited state energy, and highest photostability, enabling remarkably enhanced performance (up to >1000 TON at a low 500 ppm catalyst loading) in TTEnT photocatalysis. These findings supported by density functional theory-based calculations demonstrate that counterions have a critical role in modulating cationic transition metal-based photocatalyst potency, a parameter that should be taken into consideration also when developing energy transfer-triggered processes.
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hal-04687774 , version 1 (15-10-2024)

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Juliette Zanzi, Zachary Pastorel, Carine Duhayon, Elise Lognon, Christophe Coudret, et al.. Counterion Effects in [Ru(bpy)3](X)2-Photocatalyzed Energy Transfer Reactions. JACS Au, 2024, 4 (8), pp.3049-3057. ⟨10.1021/jacsau.4c00384⟩. ⟨hal-04687774⟩
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