Optical electron transfer through 2,7-diethynylfluorene spacers in mixed-valent complexes containing electron-rich "(η2-dppe)(η5-C5Me5)Fe" endgroups.

International audienceWe report in this communication the study of the intramolecular electron transfer through a 2,7-diethynylfluorenyl spacer in the Fe(II)/Fe(III) mixed-valent (MV) complex [(η(2)-dppe)(η(5)-C(5)Me(5))FeC≡C(2,7-C(21)H(24))C≡CFe(η(5)-C(5)Me(5))(η(2)-dppe)][PF(6)] (1[PF(6)]). The complex is generated in situ by comproportionation from its homovalent dinuclear Fe(II) and Fe(III) parents (1 and 1[PF(6)](2)). It is shown that electronic delocalization is much more effective through a 2,7-fluorenyl than through a 4,4'-biphenyl bridging unit

Assemblages organofers pour l'absorption à deux photons et l'électronique moléculaire

Au cours de cette thèse, nous nous sommes intéressés à des complexes organofers Cp*(dppe)Fe . Une première partie est consacrée à des complexes contenant l unité fluorène, principalement pour des applications en optique. Notamment, nous avons montré que le synthon organométallique éteignait la fluorescence du ligand, quel que soit le degré d oxydation du fer. L étude d une famille de complexes construits autour du fluorène, mais présentant des variations structurales ou des sites redox différents, nous a cependant permis de mettre en évidence l existence d un mécanisme d extinction de la luminescence par transfert d énergie. Par ailleurs, insérée dans des structures bimétalliques, cette unité s est avérée être un bon synthon pour l électronique moléculaire. Une seconde partie est consacrée à l étude de complexes contenant l unité pyridine, en vue d une utilisation comme métallo-ligand pour la construction de fils moléculaires par auto-assemblage. L étude de la délocalisation électronique et de spin dans des complexes pyridine et pyridinium, pris comme modèles extrêmes des unités présentes dans les structures supramoléculaires, a montré que ces complexes permettaient une bonne communication entre leurs extrémités, à l état Fe(II) et Fe(III), ce qui met en évidence le potentiel de ces molécules comme précurseurs pour la synthèse de fils par auto-assemblage. Nous avons alors obtenu une structure supramoléculaire par coordination de deux sur une porphyrine de Ru(II). L étude du complexes trimétallique mono-oxydé a mis en évidence un couplage électronique large entre les extrémités organofer, montrant ainsi que nous avions généré un fil moléculaire efficace.During this work, we have been interested in the study of Cp*(dppe)Fe organoiron complexes. A first part deals essentially with complexes bearing the fluorene unit, specially for potential applications in optics. We demonstrated that this organometallic unit quenches the fluorescence of the ligand, whatever the redox state of the iron. The study of a family of that kind of complexe, build with this unit but having some different structures or redox sites, allowed us to highlight the existence of an energy transfert quenching mecanism. Furthermore this unit appeared to be a good bridge for molecular electronics, when it is inserted in bimetallic structures. A seconde part deals with the study of complexes bearing the pyridine unit with the goal to use them as metallo-ligands to build auto-assembled molecular wires. The detailled study of the electronic and spin delocalisation in pyridine as well as pyridinium complexes (studied as extrem models for the complexation of the units which are in the supramolecular structures) showed that these Cp*(dppe)Fe complexes with an ethynylpyridine unit allowed a good ommunication between its different extremities. This study was run with Fe(II) and Fe(III) complexes and that points the potentiality of these molecules for the buiding of auto-assembled molecular wires. We then could synthesized such a structure by the coordination of two complexes in the apical positions of a Ru(II) porphyrine. The mono-oxydation of this trimetallic complexe points out the existence of a large electronic coupling between both organoiron extremities, and proved we generated a efficient molecular wire.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Design of pyridine-dicarboxamide ligands for the sensitization of europium(III) by two photon antenna effect

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Two-Photon Antenna Effect Induced in Octupolar Europium Complexes

International audienceThe synthesis of new chromophore-based pyridine-dicarboxamide ligands and related D3 symmetric europium(III) complexes is described. The photophysical properties of the ligands and complexes were investigated and interpreted using theoretical calculations (TD-DFT). Finally, the luminescence of Eu(III) was sensitized by two-photon absorption of the ligand, illustrating the two-photon antenna effect

Synthesis, structures, optical properties, and TD-DFT studies of donor-p-conjugated dipicolinic acid/ester/amide ligands

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Topological dependence of the magnetic exchange coupling in arylethynyl-bridged organometallic diradicals containing [(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(III)](+) fragments.

International audienceWe have investigated the spin distribution and determined the magnetic exchange coupling J(ab) (defined according to the following Hamiltonian: H(spin) = -2J(ab)S(a).S(b)) for three arylethynyl-bridged organoiron(III) diradicals containing [(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(III)](+) fragments. Considering the distance separating the Fe(III) centers (>or=11 A), remarkably large intramolecular magnetic interactions between unpaired spins were found for two of them. Thus, an antiferromagnetic coupling (J(ab)) of ca. -190 cm(-1) was experimentally determined for the binuclear Fe(III) species featuring a 1,4-diethynylbenzene bridge 1[PF(6)](2), while a ferromagnetic interaction of over +150 cm(-1) was evidenced for its 1,3-substitued analogue 2[PF(6)](2). We also show that a much weaker interaction (0 > J(ab) >or= -1 cm(-1)) takes place in the 4,4'-biphenyl analogue of 1[PF(6)](2) (3[PF(6)](2)), evidencing that insertion of an additional 1,4-phenylene unit in the bridge severely disrupts the magnetic communication in these diradicals. With the help of NMR and density functional theory, the magnetic properties of these compounds were rationalized and compared to those of the corresponding mononuclear Fe(III) relatives 4[PF(6)] and 5[PF(6)]. Finally, it is shown that, for all of these dinuclear Fe(III) complexes, the structural changes between singlet and triplet spin isomers remain very small regarding the carbon-rich bridge. Thus, even for a strongly coupled diradical such as 1[PF(6)](2), a dominant diradicaloid character dominates the valence-bond description of the singlet state unpaired electrons

New thiocyanato and azido adducts of the redox-active Fe(η5-C5Me5)(η2-dppe) center: Synthesis and study of the Fe(II) and Fe(III) complexes

International audienceThe new thiocyanato- (5) and azido- (6) complexes were synthesized and studied under their Fe(II) and Fe(III) redox states. For the first time among the various [Fe(η5-C5Me5)(η2-dppe)]-based cationic radicals studied so far, the magnitude and spatial orientation of the g-tensor diagonal values were experimentally determined for 5[PF6]. These data are in good agreement with those issued from a DFT modelization. The changes experienced by the electronic structure of the Fe(II) complexes subsequent to oxidation are reminiscent of these previously observed for the known arylalkynyl analogues, albeit some differences can be pointed out. Thus, the differences observed in the 1H NMR spectra of 5[PF6] and 6[PF6] are attributed to a slower electronic spin relaxation and to the differently oriented magnetic anisotropy. The sizeable spin density evidenced by DFT on the terminal atom of the ligands of the Fe(III) complexes renders these new paramagnetic metallo-ligands quite appealing for accessing larger polynuclear molecular assemblies with magnetically interacting centers

Self-assembled molecular wires from organoiron metalloligands and ruthenium tetramesitylporphyrin.

International audienceA trinuclear assembly of two (η(2)-dppe)(η(5)-C(5)Me(5))FeC≡C(4-Py) (Py = pyridyl) metalloligands apically coordinated to a ruthenium(II) tetramesitylporphyrin is demonstrated to behave as a molecular wire in the monooxidized state

Spin Distribution in Electron-Rich Piano-Stool Iron(III) Pyridylalkynyl Radical Cations Containing [(eta(2)-dppe)(eta(5)-C5Me5)FeC C](+) End Groups.

International audienceThis experimental and theoretical contribution is aimed at investigating the electronic structure of cationic electron-rich ethynylpyridyl Fe(III) derivatives of the formula [(η2-dppe)(η5-C5Me5)FeC≡C(x-C5H4N)][PF6] (x = 4, 3, 2; 1a−c[PF6]) and [(η2-dppe)(η5-C5Me5)FeC≡C(2,5-C5H3NX)][PF6] (X = Cl, Br; 2a,b[PF6]). The Mössbauer, NMR, and ESR characterization of these paramagnetic species are reported and discussed in connection with DFT results. Special emphasis is put on the electronic effect of the nitrogen atom and of the halogen substituent on the spin distribution within the pyridyl unit. It is shown that 1H NMR constitutes a straightforward empirical way to investigate the slight changes in spin distribution taking place on the heteroaryl ring

Triarylisocyanurate-Based Fluorescent Two-Photon Absorbers

International audienceThe synthesis and characterization of six triarylisocyanurates, featuring 2,7-fluorenyl or 9,10-anthracenyl groups incorporated in their peripheral arms are reported. Photophysical studies reveal that these new octupolar derivatives are more fluorescent (Φ ≥0.60 for all new compounds except for 1,3,5-tri(9H-fluoren-2-yl)-1,3,5-triazinane-2,4,6-trione 3) and present a red-shifted lowest absorption and emission compared to their known phenyl analogues of comparable size. Depending on the nature of the terminal substituent, fast intramolecular energy transfer among the three arms or localization of the excitation on a single branch occurs after population of their first singlet excited state. The latter effect was only observed in the presence of strongly electron-releasing substituents in polar media. These new chromophores are also better two-photon absorbers than the 1,4-phenylene-based isocyanurates reported so far, with cross sections σ ≥500 GM at 770 nm for 4-NPh the fluorenyl group containing (13) and the anthracenyl group containing (14) chromophores. All these spectroscopic features, analyzed with the help of quantum chemical calculations, are crucial for the design of new biphotonic fluorescent dyes