Lanthanide Dinuclear Complexes Involving Tetrathiafulvalene-3-pyridine-N-oxide Ligand: Semiconductor Radical Salt, Magnetic, and Photophysical Studies

Centro-symmetric dinuclear complexes of formula [Ln-(tta)(3)(L)](2)center dot xCH(2)Cl(2), (tta(-) = 2-thenoyltrifluoroacetonate anion, x = 0.5 for Ln = Eu (la), Tb (3), and Dy (4) and x = 0 for Ln = Eu (1b) and Nd (2)) have been synthesized using the tetrathiafulvalene-3-pyridine-N-oxide as a bridging ligand (L). X-ray structures have shown the formation of channels with CH2Cl2 solvent inside. 1 is stable with both filled channels (at 150 K) and empty channels (at room temperature). The Dy-III analogue displays a complex butterfly like hysteresis loop at 1.5 K. Photophysical properties of the coordination complexes have been studied by solution and solid-state absorption spectroscopy. Time-dependent density functional theory (TD-DFT) calculations have been carried out on the diamagnetic Y-III derivative to shed light on the absorption spectrum. For 2, the excitation of the charge transfer transitions induces line shape emission in the near-infrared spectral range assigned to F-4(3/2) -> I-4(9/2), F-4(3/2) -> I-4(11/2), and F-4(3/2) -> I-4(13/2) neodymium centered transitions. The reversible redox-activity of the ligand L makes possible an original sensitization process involving a ligand centered charge separation followed by energy transfer to the Nd-III ion upon recombination.