Tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide as Efficient Charge‐Transfer Antenna Ligand for the Sensitization of Yb^III Luminescence in a Series of Lanthanide Paramagnetic Coordination Complexes

Abstract

The tetrathiafulvalene-amido-2-pyridine-N-oxide (L) ligand has been employed to coordinate 4f elements. The architecture of the complexes mainly depends on the ionic radii of the lanthanides. Thus, the reaction of L in the same experimental protocol leads to three different molecular structure series. Binuclear [Ln(2)(hfac)(5)(O(2)CPhCl)(L)(3)]·2 H(2)O (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion, O(2)CPhCl(-)=3-chlorobenzoate anion) and mononuclear [Ln(hfac)(3)(L)(2)] complexes were obtained by using rare-earth ions with either large (Ln(III)=Pr, Gd) or small (Ln(III)=Y, Yb) ionic radius, respectively, whereas the use of Tb(III) that possesses an intermediate ionic radius led to the formation of a binuclear complex of formula [Tb(2)(hfac)(4)(O(2)CPhCl)(2)(L)(2)]. Antiferromagnetic interactions have been observed in the three dinuclear compounds by using an extended empirical method. Photophysical properties of the coordination complexes have been studied by solid-state absorption spectroscopy, whereas time-dependent density functional theory (TD-DFT) calculations have been carried out on the diamagnetic Y(III) derivative to build a molecular orbital diagram and to reproduce the absorption spectrum. For the [Yb(hfac)(3)(L)(2)] complex, the excitation at 19,600 cm(-1) of the HOMO→LUMO+1/LUMO+2 charge-transfer transition induces both line-shape emissions in the near-IR spectral range assigned to the (2)F(5/2)→(2)F(7/2) (9860 cm(-1)) ytterbium-centered transition and a residual charge-transfer emission around 13,150 cm(-1). An efficient antenna effect that proceeds through energy transfer from the singlet excited state of the tetrathiafulvalene-amido-2-pyridine-N-oxide chromophore is evidence of the Yb(III) sensitization.

Single‐Molecule Magnet Behaviour in a Tetrathiafulvalene‐Based Electroactive Antiferromagnetically Coupled Dinuclear Dysprosium(III) Complex

“…In fact the lanthanides are exciting due to their specific luminescence, in addition to their magnetic characteristics. It has been demonstrated that the IR luminescence of the Yb III ion can be sensitised by the antenna effect when the charge transfers of the TTF‐based ligands are activated 11a,e. In our case, the TTF derivatives perform several roles and can act not only as electroactive ligands but also as structural agents to isolate the magnetic centres.…”

Slow Magnetic Relaxation in a Redox‐Active Tetrathiafulvalene‐Based Ferromagnetic Dysprosium Complex

“…The two Dy III ions are bridged by two L 1 ligands in a μ 2 (η 1 ,η 2 ) coordination mode, which could be suitable for the transmission of significant magnetic interactions. Notably, for each monoanionic L 1 ligand coordinated to the lanthanide centre, one tta – anion is removed to guarantee the formation of a neutral dinuclear species 5c. The TTF cores of the L 1 and L 2 ligands are neutral.…”

Field-Induced Dysprosium Single-Molecule Magnet Involving a Fused o-Semiquinone-Extended-Tetrathiafulvalene-o-Semiquinone Bridging Triad

“…Nevertheless, the most important difference between the electronic spectra of free L and 1 was the intensity of the absorption band centered near 300 nm. This absorption band originated from the π-π* excitations localized on the hfac − anions [25]. absorption band centered near 300 nm.…”

“…absorption band centered near 300 nm. This absorption band originated from the π-π* excitations localized on the hfac − anions [25]. …”