- Proton-induced reversible modulation of the luminescent output of rhenium(I), iridium(III), and ruthenium(II) tetrazolate complexes
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One of the distinct features of metal-tetrazolate complexes is the possibility of performing electrophilic additions onto the imine-type nitrogens of the coordinated five-membered ring. These reactions, in particular, provide a useful tool for varying the main structural and electronic properties of the starting tetrazolate complexes. In this paper, we demonstrate how the use of a simple protonation-deprotonation protocol enables us to reversibly change, to a significant extent, the light-emission output and performance of a series of Re(I)-tetrazolate-based phosphors of the general formulation fac-[Re(N ∧N)(CO)3L], where N∧N denotes diimine-type ligands such as 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L represents a series of different 5-aryl tetrazolates. Indeed, upon addition of triflic acid to these neutral Re(I) complexes, a consistent blue shift (Δλmax ca. 50 nm) of the emission maximum is observed and the protonated species also display increased quantum yield values (4-13 times greater than the starting compounds) and longer decay lifetimes. This alteration can be reversed to the initial condition by further treating the protonated Re(I) complex with a base such as triethylamine. Interestingly, the reversible modulation of luminescent features by the same protonation- deprotonation mechanism appears as a quite general characteristic of photoactive metal tetrazolate complexes, even for compounds in which the 2-pyridyl tetrazolate ligands coordinate the metal center with a bidentate mode, such as the corresponding Ir(III) cyclometalates [Ir(C∧N)2L] and the Ru(II) polypyridyl derivatives [Ru(bpy)2L]+. In these cases, the protonation of the starting materials leads to red-shifted and more intense emissions for the Ir(III) complexes, while almost complete quenching is observed in the case of the Ru(II) analogues.
- Werrett, Melissa V.,Muzzioli, Sara,Wright, Phillip J.,Palazzi, Antonio,Raiteri, Paolo,Zacchini, Stefano,Massi, Massimiliano,Stagni, Stefano
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p. 229 - 243
(2014/01/23)
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- Synthesis, photophysical and electrochemical investigation of dinuclear tetrazolato-bridged rhenium complexes
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Starting from anionic tetrazole-based ligands, namely, 5-(4′- cyanophenyl)tetrazolate and 5-(4′-pyridyl)tetrazolate, mononuclear and dinuclear complexes of fac-[Re(CO)3(phen)]+ (phen = 1,10-phenanthroline) were prepared and characterized. For the mononuclear complexes, regioselective coordination of the metal fragments on the negatively charged tetrazolato ring is exclusively obtained. Coordination to the benzonitrile and pyridine groups was achieved by previous alkylation of the tetrazole ring. Dinuclear complexes were obtained by treatment of the corresponding mononuclear tetrazole-bound complexes with fac-[Re(CO) 3(phen)(THF)]+. The second rhenium fragment coordinated either to the pyridine ring or, in the case of the benzonitrile ligand, to the tetrazole ring. The electrochemical properties were probed in an imidazolium ionic liquid, highlighting reduction processes centered on the phen ligand and oxidation processes localized on the metal. The photophysical properties of the complexes are characterized by phosphorescent emission from triplet metal-to-ligand charge transfer excited states, with trends in the lifetime and quantum yield in qualitative agreement with the energy gap law. The two dinuclear complexes show almost superimposable emission profiles: in the 5-(4′-cyanophenyl)tetrazolate-bridged complex, the two metal fragments coordinated to the tetrazole are equivalent and share a positive charge of +1. On the other hand, the photophysical properties of the 5-(4′-pyridyl) tetrazolate-bridged dinuclear complex suggest energy transfer between the two metal centers.
- Wright, Phillip J.,Muzzioli, Sara,Werrett, Melissa V.,Raiteri, Paolo,Skelton, Brian W.,Silvester, Debbie S.,Stagni, Stefano,Massi, Massimiliano
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p. 7566 - 7578
(2013/01/15)
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