RESUMEN
The 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 (ΦF ≥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 σ2 ≥500â GM at 770â nm for 4-NPh2 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.
RESUMEN
We 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.
RESUMEN
A 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.
RESUMEN
We 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.
RESUMEN
The synthesis of new chromophore-based pyridine-dicarboxamide ligands and related D3 symmetric europium(III) complexes is described. The photophysical properties of the ligands and the complexes were thoroughly investigated and interpreted on the basis of 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 phenomenon.