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·xCH2Cl2, (tta– = 2-thenoyltrifluoroacetonate anion, x = 0.5 for Ln = Eu (1a), 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 DyIII 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 YIII 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 4F3/2→ 4I9/2, 4F3/2→ 4I11/2, and 4F3/2→ 4I13/2 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 NdIII ion upon recombination.