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PH-Driven Mechanistic Switching from Electron Transfer to Energy Transfer between [Ru(bpy)3]2+ and Ferrocene Derivatives.


ABSTRACT: The metal-to-ligand charge transfer excited states of [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) may be deactivated via energy transfer or electron transfer with ferrocene derivatives in aqueous conditions. Stern-Volmer quenching analysis revealed that the rate constant for [Ru(bpy)3]2+ excited-state quenching depends on solution pH when a ferrocenyl-amidinium derivative (Fc-am) containing a proton-responsive functionality tethered to the ferrocene center was present. By contrast, the rate constant with which the [Ru(bpy)3]2+ excited state is quenched by an analogous ferrocene derivative (ferrocenyl-trimethylammonium, Fc-mam) that lacks a protonic group does not depend on pH. These results show that the presence (or absence) of a readily transferrable proton modulates quenching rate constants in bimolecular events involving [Ru(bpy)3]2+ and ferrocene. More surprisingly, transient absorption spectroscopy reveals that the mechanism by which the [Ru(bpy)3]2+ excited state is quenched by Fc-am appears to be modulated by solution proton availability, switching from energy transfer at low pH when Fc-am is protonated, to electron transfer at high pH when Fc-am is deprotonated. The mechanistic switching that is observed for this system cannot be aptly explained using a simple driving force dependence argument, suggesting that more subtle factors dictate the pathway by which the [Ru(bpy)3]2+ excited state is deactivated by ferrocene in aqueous solutions.

SUBMITTER: Drolen C 

PROVIDER: S-EPMC6192533 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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pH-Driven Mechanistic Switching from Electron Transfer to Energy Transfer between [Ru(bpy)<sub>3</sub>]<sup>2+</sup> and Ferrocene Derivatives.

Drolen Claire C   Conklin Eric E   Hetterich Stephen J SJ   Krishnamurthy Aditi A   Andrade Gabriel A GA   Dimeglio John L JL   Martin Maxwell I MI   Tran Linh K LK   Yap Glenn P A GPA   Rosenthal Joel J   Young Elizabeth R ER  

Journal of the American Chemical Society 20180802 32


The metal-to-ligand charge transfer excited states of [Ru(bpy)<sub>3</sub>]<sup>2+</sup> (bpy = 2,2'-bipyridine) may be deactivated via energy transfer or electron transfer with ferrocene derivatives in aqueous conditions. Stern-Volmer quenching analysis revealed that the rate constant for [Ru(bpy)<sub>3</sub>]<sup>2+</sup> excited-state quenching depends on solution pH when a ferrocenyl-amidinium derivative (Fc-am) containing a proton-responsive functionality tethered to the ferrocene center wa  ...[more]

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