Luc Jacquet

Spectroelectrochemical characteristics and photophysics of a series of RuII complexes with 1,4,5,8,9,12-hexaazatriphenylene: effects of polycomplexation

A study of the photophysical mechanisms controlling the luminescence lifetimes of a series of RuII complexes based on the same [Ru3+–hat˙–]* luminophore (hat = 1,4,5,8,9,12-hexaazatriphenylene), and extending from monometallic building blocks to polynuclear compounds, is presented, together with the relevant spectroscopic and redox data. The parameters which characterise these different mechanisms, i.e. the radiative and nonradiative deactivation rate constants of the 3MLCT (metal to ligand charge transfer) state and the thermal activation from this state to the 3MC (metal centred) and/or to another 3MLCT state, have been determined from the analyses of the curves obtained by plotting the lifetimes or intensities of luminescence as a function of temperature. The mathematical and experimental limitations of the analysis method have been investigated and determination of the parameters has been improved by using a new global analysis algorithm. Interestingly the comparison of the data for the monometallic and polynuclear complexes indicates that the (Ru3+–hat˙–)* luminophore, which is common for the whole series, presents characteristics that change when the hat becomes a bridging ligand, i.e. those that depend on the vibration modes of the complex. Moreover, for these polynuclear compounds, there is no contribution of the 3MC state to the mechanism of control of the luminescence lifetime.

Photoadduct between tris(1,4,5,8-tetraazaphenanthrene)ruthenium(II) and guanosine monophosphate–a model for a new mode of covalent binding of metal complexes to DNA

Visible light irradiation of [Ru(TAP)3]2+(TAP = 1,4,5,8 -tetraazaphenanthrene) in aqueous solutions containing 5′-guanosine-monophosphate (GMP) and subsequent treatment with 1 mol dm–3 HCl yields Ru(TAP)2(2-TAP-G)2+, in which the guanine moiety is bound via N-2 to C-2 of one of the TAP ligands.

Quenching of excited polyazaaromatic Ru(II) complexes by oxygen: evidence for an electron transfer process by photoelectrochemical study

Abstract The possible contribution of an electron transfer process to the quenching of excited Ru(II) polypyridyl complexes by oxygen has been the subject of controversy for many years; the existence of this process is re-examined in this work with new polyazaaromatic complexes and by a photoelectrochemical (PEC) method. The luminescence quenching rate constants kQ by oxygen in acetonitrile for a series of polyazaaromatic complexes with 1,4,5,8-tetraazaphenanthrene (tap), 1,4,5,8,9,12-hexaazatriphenylene (hat) and 2,2′-bipyridine (bpy) as ancillary ligand, can clearly be correlated with the oxidation potentials in the excited state. A PEC study of the quenching of Ru(bpy)32+* by oxygen in acidic medium allows determination of the quenching rate constant via the measurements of cathodic photocurrents induced at a transparent SnO2 electrode. These two investigations show that the electron transfer mechanism is certainly involved in the luminescence quenching of these Ru(II) complexes by oxygen and that the energy transfer contribution becomes rather weak for the more reducing excited complexes.

Resonance-Raman probing of the interaction between dipyridophenazine complexes of ruthenium(II) and DNA

The resonance-Raman spectroscopic technique is an effective probe of the interaction between dipyridophenazine (dppz) complexes of ruthenium(II) and calf-thymus DNA, providing evidence that DNA addition results in changes to electronic transitions of the intercalating dppz ligand in both ground and excited states.

Formation of a covalently-linked bimetallic compound upon irradiation of tris(1,4,5,8-tetraazaphenanthrene)ruthenium(II) in the presence of 5′-guanosine-monophosphate

Abstract A new type of binuclear Ru(II) complex [Ru(TAP) 2 (TAP-TAP)Ru(TAP) 2 ] 4+ ( 1 ) (TAP-TAP=2,2′-bis(1,4,5,8-tetraazaphenanthrene)) produced by photo-reaction of Ru(TAP) 3 2+ in the presence of 5′-guanosine-monophosphate (5′-GMP) has been isolated and characterised. The formation of 1 is proposed to proceed via mono-reduced Ru(TAP) 3 2+ , i.e. [Ru 2+ (TAP) 2 (TAP ⋅− )] + . The emission lifetime of 1 is much greater than that of Ru(TAP) 3 2+ , consistent with an increased energy gap between the 3 MLCT and 3 MC states in 1 . This arises because of stabilisation of its 3 MLCT state due to the localisation of the excited state electron on the TAP-TAP ligand.

Transient Resonance RamanStudies of Ru(II) Complexes in DNAand in Homogeneous Media

Transient resonance Raman (TR2) spectroscopy has been used to investigate the metalligand charge-transfer (MLCT) excited states of Ru(II) polypyridyl complexes inDNAand in homogeneous solution. In DNA, complexes of the type [Ru(L)2(L′)]2

Excited state properties of bis-tetraazaphenanthrene-Ru (II) diad complexes with a ferrocenyl unit

Abstract The excited state properties of the diad complexes Ru(tap) 2 (ppFe) 2+ and Ru(bpy) 2 (ppFc) 2+ (tap, 1,4,5,8-tetraazaphenanthrene; bpy, 2,2′-bipyridine), bearing a reducing ferrocenyl (Fe) centre on a derivatized (pyridine)pyrazole (pp) ligand, were compared with those of the corresponding complexes without an Fc unit. For these latter complexes, the existence of intermolecular photoelectron transfer with added ferrocene was clearly demonstrated. However, direct evidence for intramolecular photoelectron transfer in Ru(bpy) 2 (ppFc) 2+ and Ru(tap) 2 (ppFc) 2+ could not be obtained unambigously. Although the absence of luminescence in these diad complexes indicated the existence of this intramolecular process, laser flash photolysis did not allow the detection of a reduced complex entity in most experimental conditions. Only flash photolysis of Ru(bpy) 2 (ppFc) 2+ in water generated a long-lived intermediate with the characteristics spectral features of the radical anion bpy − . Indirect arguments, such as the formation of a product on illumination of both diad complexes, were in favour of a photoreaction induced by intramolecular electron transfer.