In Solution Sensitization of Er(III) Luminescence by the 4-Tetrathiafulvalene-2,6-pyridinedicarboxylic Acid Dimethyl Antenna Ligand

Solid-State Near-Infrared Circularly Polarized Luminescence from Chiral YbIII -Single-Molecule Magnet

A field-induced chiral Yb^III Single-Molecule Magnet (SMM) displayed an unprecedented near-infrared circularly polarized luminescence (NIR-CPL) in the solid-state. The bridging bis(1,10-phenantro[5,6b])tetrathiafulvalene triad (L) allowed an efficient sensitization of the NIR ² F_5/2 →² F_7/2 emission while the NIR-CPL is associated to the f-f transitions of the Yb^III ion bearing chiral β-diketonate derived-camphorate ancillary ligands.

Pyridine-2,6-Dicarboxylic Acid Esters (pydicR2) as O,N,O-Pincer Ligands in CuII Complexes

The pyridine-2,6-carboxylic esters pydicR2 with R = Me or Ph form the unprecedented mononuclear CuII complexes [Cu(pydicR2)Cl3]− in one-pot reactions starting from pyridine-2,6-carboxychloride pydicCl2, CuII chloride, and NEt3 in MeOH or PhOH solution under non-aqueous conditions. The triethylammonium salts (HNEt3)[Cu(pydicR2)Cl3] were isolated. The methyl derivative could be crystallized to allow a XRD structure determination. Both structures were optimized using DFT calculations in various surroundings ranging from gas phase and the non-coordinating solvent CH2Cl2 to the weakly coordinating acetone and well-coordinating solvents acetonitrile (MeCN) or dimethylformamide (DMF), while detailed calculation showed the charge distribution, dipole moments, and HOMO–LUMO gap energies changing upon solvation. According to these calculations, the ion pairs and the anionic CuII complexes were stable, which shows only Cu–Cl bond elongation and weakening of the charge transfer between the anionic complex and the cation as solvents become polar. Synthesis attempts in the presence of water yielded the CuII complexes [Cu(pydic)(OH2)2]n and [Cu(OH2)6][{Cu(pydic)}2(µ-Cl)2], which results from pydicCl2 hydrolysis. Alternatively, the new pydic(IPh)2 (IPh = 2-iodo-phenyl) ester ligand was synthesized and reacted with anhydrous CuCl2, which yields the new binuclear complex [{Cu(pydic(IPh)2)Cl}2(µ-Cl)2]. EPR spectroscopy of the solid compounds reveals typical axial spectra in line with the observed and DFT calculated geometries. Cyclic voltammetry and UV–vis absorption spectroscopy in solution are in line with un-dissociated complex species [Cu(pydicR2)Cl3]−.

Visible light sensitized near-infrared luminescence of ytterbium via ILCT states in quadruple-stranded helicates

Quadruple-stranded helicates show visible light sensitized near-infrared luminescence of ytterbium via ILCT states.

Lanthanide complexes involving multichelating TTF-based ligands

The TTF-based skeleton could be alkylated with either the di(pyrazol-1-yl)-4-pyridyl (L1) or dimethyl-2,2′-bipyridine (L2) to design multichelating ligands. The ([Yb₂(hfac)₆(L1)]·2(CH₂Cl₂)·C₆H₁₄ (1) and [Ln₂(hfac)₆(L2)]·CH₂Cl₂ (Ln = Yb (2) and Dy (3)) complexes which display either SMM behaviour with the hysteresis loop at 0.5 K or multi-NIR emissions.

Insight into the roles of structures and energy levels of mono- and bis-β-diketones on sensitizing Nd(iii) NIR-luminescence

Three neodymium complexes Nd(TTA)3(DMSO)2 (1, TTA = 2-thenoyltrifluoroacetone), Nd2(BDT)3(DMSO)6 (2, BDT = bis(4,4,4-trifluoro-1,3-dioxobutyl)thiophene) and Nd2(BTT)3(DMSO)4 (3, BTT = bis(4,4,4-trifluoro-1,3-dioxobutyl)(2,2'-bithiophene)) constructed from three thiophene-based β-diketonate ligands, were prepared for the purpose of building the relationships between the structures, energy levels of the complexes and NIR luminescence properties of Nd(iii) ions. X-ray crystallographical analysis reveals that complex 1 is a mononuclear structure, the central Nd(iii) ion is coordinated by eight oxygen atoms from three mono-β-diketones (TTA) and two DMSO, whereas, complexes 2 and 3 adopt triple-stranded dinuclear structures, in which the two Nd(iii) ions are wrapped by three bis-β-diketones, the central Nd(iii) ions are nine and eight coordinated by oxygen atoms from ligands and the coordinated DMSO molecules. The photophysical properties related to the electronic transition are characterized by the absorbance spectra, the excitation spectra, the phosphorescence spectra, the emission spectra, the emission quantum yields, and the emission lifetimes. The luminescence quantum yields experiment reveals that the dinuclear complexes (0.49% and 0.33% for 2 and 3) show higher luminescence efficiencies compared to the mononuclear complex 1 (0.22%). This enhancement is mainly attributed to their binuclear structures, which effectively represses the nonradiative transition caused by high-energy oscillators in ligands and/or solvents. On the other hand, the energy level matching also plays an important role in this enhancement.

Lanthanide ion and tetrathiafulvalene-based ligand as a "magic" couple toward luminescence, single molecule magnets, and magnetostructural correlations

The synthesis of molecules featuring different properties is a perpetual challenge for the chemists' community. The coexistence and even more the synergy of those properties open new perspectives in the field of molecular devices and molecular electronics. In that sense, coordination chemistry contributed to the development of new functional molecules through, for instance, single-molecule magnets (SMMs) and light emitting molecules with potential applications in high capacity data storage and OLEDs, respectively. The appealing combination of both electronic properties into one single object may offer the possibility to have magnetized luminescent entities at nanometric scale. To that end, lanthanides seem to be one of the key ingredients since their peculiar electronic structures endow them with specific magnetic and luminescence properties. Indeed, lanthanides cover a wide range of emission wavelengths, from infrared to UV, which add up to a large variety of magnetic behaviors, from the fully isotropic spin (e.g., Gd(III)) to highly anisotropic magnetic moments (e.g., Dy(III)). In lanthanide complexes, ligands play a fundamental role because on one hand they govern the orientation of the magnetic moment of anisotropic lanthanides and on the other hand they can sensitize efficiently the luminescence. The design of appropriate organic ligands to elaborate such chemical objects with the desired property appears to be essential but remains a perpetual challenge. In this Account, we describe the design of lanthanide-based complexes that emit light, behave as SMMs, or combine both properties. We have paid peculiar attention to the design of ligands based on the tetrathiafulvalene (TTF) moiety. TTF and its derivatives are well-known chemical entities, stable at different oxidation states, and employed mainly in the synthesis of molecular conductors and superconductors. In addition to their redox properties, TTF-based derivatives act as organic chromophores for the sensitization of visible and near-infrared (NIR) luminescence of lanthanides. The mechanism of sensitization involves either antenna effect (energy transfer from the excited state) or photoinduced electron transfer. TTF-based ligands act also as structural agents in the conception of SMM in crystals. Such objects are obtained with the highly anisotropic Dy(III) ion in crystalline phase as well as in frozen solution with magnetic memory at helium-4 temperature (4 K). We highlight the influence of the magnetic dilution (both in amorphous solution and in diamagnetic crystalline matrix) and, particular case of dysprosium based SMMs, the effect of metal-centered isotope enrichment on the SMM properties. Our aim is not only to realize functional molecules but to rationalize both luminescence and magnetic properties on the basis of the structure of the molecules. These two properties are intimately intricate and governed by the electronic structure, which can be calculated and interpreted using modern quantum chemistry tools.

Luminescence and single-molecule magnet behavior in lanthanide complexes involving a tetrathiafulvalene-fused dipyridophenazine ligand

The reaction between the TTF-fused dipyrido[3,2-a:2',3'-c]phenazine (dppz) ligand (L) and 1 equiv of Ln(hfac)3·2H2O (hfac(-) = 1,1,1,5,5,5-hexafluoroacetyacetonate) or 1 equiv of Ln(tta)3·2H2O (tta(-) = 2-thenoyltrifluoroacetonate) (Ln(III) = Dy(III) or Yb(III)) metallic precursors leads to four mononuclear complexes of formula [Ln(hfac)3(L)]·C6H14 (Ln(III) = Dy(III) (1), Yb(III) (2)) and [Ln(tta)3(L)]·C6H14 (Ln(III) = Dy(III) (3), Yb(III) (4)), respectively. Their X-ray structures reveal that the Ln(III) ion is coordinated to the bischelating nitrogenated coordination site and adopts a D4d coordination environment. The dynamic magnetic measurements show a slow relaxation of the Dy(III) magnetization for 1 and 3 with parameters highlighting a slower relaxation for 3 than for 1 (τ0 = 4.14(±1.36) × 10(-6) and 1.32(±0.07) × 10(-6) s with Δ = 39(±3) and 63.7(±0.7) K). This behavior as well as the orientation of the associated magnetic anisotropy axes have been rationalized on the basis of both crystal field splitting parameters and ab initio SA-CASSCF/RASSI-SO calculations. Irradiation of the lowest-energy HOMO → LUMO ILCT absorption band induces a (2)F5/2 → (2)F7/2 Yb-centered emission for 2 and 4. For these Yb(III) compounds, Stevens operators method has been used to fit the thermal variation of the magnetic susceptibilities, and the resulting MJ splittings have been correlated with the emission lines.

Current advances in fused tetrathiafulvalene donor–acceptor systems

Development and applications of tetrathiafulvalene-fused electron donor–acceptor systems will be covered within this tutorial review.

Magnetic and photo-physical investigations into DyIII and YbIII complexes involving tetrathiafulvalene ligand

Three TTF-based complexes have been elaborated using β-diketonate Dy^III and Yb^III precursors. [Yb(tta)₃(L)]·2CH₂Cl₂ enlarges the scarce series of redox-active luminescent single-molecule magnets with correlation between emissive and magnetic properties.

Structural effects on the photophysical properties of mono-β-diketonate and bis-β-diketonate EuIII complexes

Two mononuclear and binuclear europium complexes with similar chemical structures show structure-dependent photophysical properties.

Unprecedented sensitization of visible and near-infrared lanthanide luminescence by using a tetrathiafulvalene-based chromophore

Ligand L was synthesized and then coordinated to [Ln(hfac)3]⋅2 H2O (Ln(III)=Tb, Dy, Er; hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion) and [Ln(tta)3]⋅2 H2O (Ln(III)=Eu, Gd, Tb, Dy, Er, Yb; tta(-)=2-thenoyltrifluoroacetonate) to give two families of dinuclear complexes [Ln2(hfac)6(L)]⋅C6H14 and [Ln2(tta)6(L)]⋅2 CH2Cl2. Irradiation of the ligand at 37,040 cm(-1) and 29,410 cm(-1) leads to tetrathiafulvalene-centered and 2,6-di(pyrazol-1-yl)-4-pyridine-centered fluorescence, respectively. The ligand acts as an organic chromophore for the sensitization of the infrared Er(III) (6535 cm(-1)) and Yb(III) (10,200 cm(-1)) luminescence. The energies of the singlet and triplet states of L are high enough to guarantee an efficient sensitization of the visible Eu(III) luminescence (17,300-14,100 cm(-1)). The Eu(III) luminescence decay can be nicely fitted by a monoexponential function that allows a lifetime estimation of (0.49±0.01) ms. Finally, the magnetic and luminescence properties of [Yb2(hfac)6(L)]⋅C6H14 were correlated, which allowed the determination of the crystal field splitting of the (2)F(7/2) multiplet state with M(J)=±1/2 as ground states.

Multiplicate sensitization of novel near-infrared luminescent linear copolymers based on Er, Nd and Yb-complexes

A series of novel near-infrared (NIR) luminescent linear copolymers (PCzLnQL₂) covalently linked with Ln-complexes were synthesized and characterized. The copolymers show broadband sensitized and highly efficient NIR luminescence.

Chiroptical, linear, and second-order nonlinear optical properties of binaphthol derivatives

We have investigated the chiroptical, linear, and second-order nonlinear optical (NLO) properties of seven binaphthol derivatives and elucidated structure-property relationships from the micromechanism for the first time. The excitation energies, oscillator strengths, and rotational strengths of the 150 lowest energy electron excitations for the most stable conformers have been calculated at TDB3LYP/cc-pVDZ level of theory. The experimental UV-vis absorption energies were reproduced well by our calculations. The simulated circular dichroism (CD) spectra and calculated optical rotation (OR) values are in reasonable agreement with experimental ones. These results demonstrate that TDDFT calculations can not only describe the electron transition property but also can be used to assign the absolute configurations (ACs) of binaphthol derivatives with high confidence. Whereas OR values are more sensitive to the molecular structures than CD spectra. The electron transition property and chiroptical origin have been assigned and analyzed. These derivatives possess remarkably large molecular first hyperpolarizabilities, especially compound 7 which has a value of 241.65 × 10(-30) esu. This value is about 60 times as large as that of highly π-delocalized phenyliminomethyl ferrocene complex. Moreover, compound 6 exhibits pronounced different second-order NLO response values from neutral state to the two cationic states (6(2+) and 6(4+)), which indicates that this compound could act as a potential NLO switch material. The cooperativity of intramolecular charge transfer of the studied compounds was also discussed.