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Early photophysical events of a ruthenium(II) molecular dyad capable of performing photochemical water oxidation and of its model compounds

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Abstract

The early photophysical events occurring in the dinuclear metal complex [(ttb-terpy)(I)Ru(μ-dntpz)Ru(bpy)2]3+ (2; ttb-terpy = 4,4′,4′′-tri-tert-butyl-terpy; bpy = 2,2′-bipyridine; dntpz = 2,5-di-(1,8-dinaphthyrid-2-yl)pyrazine) – a species containing the chromophoric {(bpy)2Ru(μ-dntpz)}2+ subunit and the catalytic {(I)(ttb-terpy)Ru(μ-dntpz)}+ unit, already reported to be able to perform photocatalytic water oxidation – have been studied by ultrafast pump–probe spectroscopy in acetonitrile solution. The model species [Ru(bpy)2(dntpz)]2+ (1), [(bpy)2Ru(μ-dntpz)Ru(bpy)2]4+ (3), and [(ttb-terpy)(I)Ru((μ-dntpz)Ru[(ttb-terpy)(I)]2+ (4) have also been studied. For completeness, the absorption spectra, redox behavior of 1–4 and the spectroelectrochemistry of the dinuclear species 2–4 have been investigated. The usual 3MLCT (metal-to-ligand charge transfer) decay, characterized by relatively long lifetimes on the ns timescale, takes place in 1 and 3, whose lowest-energy level involves a {(bpy)2Ru(dntpz)}2+ unit, whereas for 2 and 4, whose lowest-energy excited state involves a 3MLCT centered on the {(I)(ttb-terpy)Ru(μ-dntpz)}+ subunit, the excited-state lifetimes are on the ps timescale, possibly involving population of a low-lying 3MC (metal-centered) level. Compound 2 also exhibits a fast process, with a time constant of 170 fs, which is attributed to intercomponent energy transfer from the MLCT state centered in the {(bpy)2Ru(μ-dntpz)}2+ unit to the MLCT state involving the {(I)(ttb-terpy)Ru(μ-dntpz)}+ unit. Both the intercomponent energy transfer and the MLCT-to-MC activation process take place from non-equilibrated MLCT states.

Graphical abstract: Early photophysical events of a ruthenium(ii) molecular dyad capable of performing photochemical water oxidation and of its model compounds

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Publication details

The article was received on 19 Nov 2018, accepted on 15 Feb 2019 and first published on 18 Feb 2019


Article type: Paper
DOI: 10.1039/C8PP00530C
Citation: Photochem. Photobiol. Sci., 2019, Advance Article

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    Early photophysical events of a ruthenium(II) molecular dyad capable of performing photochemical water oxidation and of its model compounds

    F. Nastasi, A. Santoro, S. Serroni, S. Campagna, N. Kaveevivitchai and R. P. Thummel, Photochem. Photobiol. Sci., 2019, Advance Article , DOI: 10.1039/C8PP00530C

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