Early photophysical events of a ruthenium(ii) molecular dyad capable of performing photochemical water oxidation and of its model compounds. Issue 9 (22nd February 2019)

• Record Type: Journal Article
• Authors: Nastasi, Francesco; Santoro, Antonio; Serroni, Scolastica; Campagna, Sebastiano; Kaveevivitchai, Nattawut; Thummel, Randolph P.
• Is Part Of: Photochemical & photobiological sciences. Volume 18:Issue 9(2019)
• Page Start: 2164
• Page End: 2173
• Publication Date: 2019-02-22
• Subjects: Photochemistry -- Periodicals; Photobiology -- Periodicals; 541.35
• DOI: 10.1039/c8pp00530c
• Languages: English
• ISSNs: 1474-905X

Abstract

Abstract : Early events in a water oxidation chromophore-catalyst species are studied; ultrafast energy transfer occurs from the chromophore to the catalytic unit. 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)2 Ru(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)2 Ru(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 of1–4 and the spectroelectrochemistry of the dinuclear species2–4 have been investigated. The usual 3 MLCT (metal-to-ligand charge transfer) decay, characterized by relatively long lifetimes on the ns timescale, takes place in1 and3, whose lowest-energy level involves a {(bpy)2 Ru(dntpz)} 2+ unit, whereas for2 and4, whose lowest-energy excited state involves a 3 MLCT 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 3 MC (metal-centered) level. Compound2 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)2 Ru(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.