Terpyridyl-Imidazole Based Ligand Coordinated to Ln(Hexafluoroacetyl acetonate)3 Core: Synthesis, Structural Characterization, Luminescence Properties, and Thermosensing Behaviors in Solution and PMMA Film

A new array of ternary lanthanide complexes of the form [Ln(hfa)3(tpy-HImzphen)] have been synthesized and thoroughly characterized wherein Ln = LaIII (1), EuIII (2), SmIII (3), and TbIII (4); hfa = hexafluoroacetylacetonate; and tpy-HImzphen = 2-(4-[2,2':6',2″]terpyridin-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole. Incorporation of tpy-HImzphen onto the Ln-hfa moiety induced a bathochromic shift of the absorption window of the complexes into the visible region. Extensive investigations of the luminescence characteristics have been conducted both at RT and at 77 K to understand the deactivation pathways of the complexes. Both steady-state and time-resolved emission spectral behaviors indicate four distinctive behaviors upon incorporation of tpy-HImzphen onto the lanthanide core, viz., a huge red-shift of the ligand-centered peak for LaIII; almost complete energy transfer for EuIII; very little energy transfer for SmIII, while reverse energy transfer in the case of TbIII. In addition, the EuIII-complex exhibits its excellence in luminescence thermometry in the solution state as well as in poly(methyl methacrylate) (PMMA) thin films. The thermosensitive luminescence response in solution was further utilized to mimic set-reset flip-flop logic operation. A plausible energy transfer scheme has been devised to explain dissimilar luminescence behaviors in the complexes. The role of LMCT was also considered for the observed thermosensing property of the Eu(III) complex.

Synthesis, characterization, luminescence properties and deciphering the role of a terpyridyl-imidazole based ligand in the dissimilar luminescence sensitization of ternary lanthanide(III) tris-(β-diketonate) complexes

We designed four ternary lanthanide tris-(β-diketonate) complexes of the form [Ln(tta)3(tpy-HImzphen)], where Ln = LaIII, EuIII, SmIII and TbIII; tta = (2-theonyltrifluoroacetonate) and tpy-HImzphen = 2-(4-[2,2':6',2'']terpyridin-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole. All the complexes have been thoroughly characterized by standard analytical tools and spectroscopic techniques including single crystal X-ray diffraction. In situ generation of the complexes was also monitored via absorption and emission spectroscopy upon incremental addition of the respective lanthanide precursor {Ln(tta)3(H2O)2} to the dichloromethane solution of the terpyridyl-imidazole ligand. The photophysical behaviors of all the complexes were thoroughly investigated via absorption and both steady-state and time-resolved emission spectroscopic techniques. The emission spectral measurements were carried out at both room temperature and 77 K to understand the deactivation dynamics of the excited states and elucidate the distinctive luminescence responses from the four lanthanide metal ions owing to the introduction of the terpyridyl-based ancillary ligand.

Organometallic Ir(III) complexes: post-synthetic modification, photophysical properties and binuclear complex construction

Two methods of post-synthetic modification (Suzuki coupling and CuAAC click-reaction) were applied to Ir(III) complexes [Ir(C^{^}N)₂N^{^}N]⁺ to provide the second highly selective donor site. One family of functionalized complexes was used to demonstrate the potential of post-synthetic modification for controlled construction of d-d and d-f binuclear complexes. The complexes obtained were characterized by CHN elemental analysis, NMR spectroscopy, ESI mass-spectrometry, FTIR spectroscopy and single crystal X-ray diffraction analysis. By means of XPS and NEXAFS spectroscopy the coordination of diimine donor site to the Ln(III) centre has been definitely confirmed. The photophysical properties of mono- and binuclear complexes were carefully investigated, and the evolution of luminescent characteristics during the formation of a system of connected metallocenters is also discussed. TDDFT calculations were used to describe the luminescence mechanism and to confirm the conclusions made on the basis of experimental data.

Perfluoroalkyl Chain Length Effect on Crystal Packing and [LnO8] Coordination Geometry in Lanthanide-Lithium β-Diketonates: Luminescence and Single-Ion Magnet Behavior

Functionalized perfluoroalkyl lithium β-diketonates (LiL) react with lanthanide(III) salts (Ln = Eu, Gd, Tb, Dy) in methanol to give heterobimetallic Ln-Li complexes of general formula [(LnL₃)(LiL)(MeOH)]. The length of fluoroalkyl substituent in ligand was found to affect the crystal packing of complexes. Photoluminescent and magnetic properties of heterobimetallic β-diketonates in the solid state are reported. The effect of the geometry of the [LnO₈] coordination environment of heterometallic β-diketonates on the luminescent properties (quantum yields, phosphorescence lifetimes for Eu, Tb, Dy complexes) and single-ion magnet behavior (U_eff for Dy complexes) is revealed.

Variable Dimensionality of Europium(III) and Terbium(III) Coordination Compounds with a Flexible Hexacarboxylate Ligand

A reaction between 4,4',4″-(benzene-1,3,5-triyltris(oxy))triphthalic acid (H₆L) and lanthanide(III) nitrates (Ln = Eu³⁺, Tb³⁺) in water under the same conditions gave a molecular coordination compound [Tb(H_4.5L)₂(H₂O)₅]∙6H₂O in the case of terbium(III) and a one-dimensional linear coordination polymer {[Eu₂(H₃L)₂(H₂O)₆]∙8H₂O}_n in the case of europium(III). The crystal structures of both compounds were established by single-crystal X-ray diffraction, and they were further characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. The compounds demonstrated characteristic lanthanide-centered photoluminescence. The lanthanide-dependent dimensionality of the synthesized compounds, which are the first examples of the coordination compounds of hexacarboxylic acid H₆L demonstrates its potential as a linker for new coordination polymers.

Optical Multisensor System Based on Lanthanide(III) Complexes as Near-Infrared Light Sources for Analysis of Milk

Optical multisensor systems are easy-to-use and inexpensive analytical devices. In this work, we propose an optical multisensor system based on the luminescence of Nd(III) and Yb(III) complexes in the near-infrared (NIR) spectral region. The observed emission bands play the role of secondary light sources for further analysis of milk—for the determination of fat content and for the recognition of adulteration. The samples for analysis were prepared by putting a drop of milk upon a thin glass covering the powdered mixture of lanthanide complexes, which were excited by a light-emitting diode (LED) in the ultraviolet region (the maximum intensity at 365 nm). The diffuse-reflectance spectra of samples were acquired in the short-wave NIR range 750–1100 nm using a portable NIR spectrometer. The developed optical system was tested using two sets of milk samples with varying concentration levels of fat and added urea. The obtained spectral data were analyzed using a number of multivariate prediction and classification methods of chemometrics and the results were statistically compared. The regression and classification model performances achieved in this proof-of-concept study illustrate the feasibility of the optical multisensor analysis based on luminescent light sources in the short-wave NIR range, in particular, for their application in the dairy.

The Tail Wags the Dog: The Far Periphery of the Coordination Environment Manipulates the Photophysical Properties of Heteroleptic Cu(I) Complexes

In this work we show, using the example of a series of [Cu(Xantphos)(N^N)]+ complexes (N^N being substituted 5-phenyl-bipyridine) with different peripheral N^N ligands, that substituents distant from the main action zone can have a significant effect on the physicochemical properties of the system. By using the C≡C bond on the periphery of the coordination environment, three hybrid molecular systems with -Si(CH3)3, -Au(PR3), and -C2HN3(CH2)C10H7 fragments were produced. The Cu(I) complexes thus obtained demonstrate complicated emission behaviour, which was investigated by spectroscopic, electrochemical, and computational methods in order to understand the mechanism of energy transfer. It was found that the -Si(CH3)3 fragment connected to the peripheral C≡C bond changes luminescence to long-lived intra-ligand phosphorescence, in contrast to MLCT phosphorescence or TADF. The obtained results can be used for the design of new materials based on Cu(I) complexes with controlled optoelectronic properties on the molecular level, as well as for the production of hybrid systems.

Highly luminescent mixed-ligand bimetallic lanthanoid(III) complexes for photovoltaic applications

Six new mixed-ligand bimetallic complexes [Eu₂(bz)₄(tta)₂(phen)₂] (1), [Gd₂(bz)₄(tta)₂(phen)₂] (2), [EuTb(bz)₄(tta)₂(phen)₂] (3), [EuGd(bz)₄(tta)₂(phen)₂] (4), [Eu_1,2Gd_0,8(bz)₄(tta)₂(phen)₂] (5) and [Eu_1,6Gd_0,4(bz)₄(tta)₂(phen)₂] (6) have been prepared with the Eu³⁺, Gd³⁺ and Tb³⁺ ions and the benzoate (bz^-), 2-thenoyltrifluoroacetonate (tta^-) and the 1,10-phenanthroline (phen) ligands. The compounds combine highly efficient antennas to obtain highly luminescent complexes to enhance solar cell efficiency. The benzoate ligand has been chosen to take its advantage as a bridging ligand to end up with bimetallic complexes to study the effect of combining two metal ions in the luminescent molecule. The structure of 1 was obtained by single-crystal X-ray diffraction, and 1-6 were found to be isostructural by powder X-ray diffraction analysis. The photophysical properties were studied by the absorbance and emission spectra and emission lifetimes. The magnetic properties of 2 were studied, and we found intramolecular antiferromagnetic interactions between the Gd³⁺ ions. We prepared luminescent down-shifting layers (LDSL) with the 1, 3-6 complexes embedded in ethylene-vinyl-acetate and studied their effect in the external quantum efficiency (EQE) and intensity-voltage (I-V) plots of a solar mini-module. We found that LDSL containing the bimetallic complexes 3 and 6 enhance the efficiency of the solar mini-module from 11.26(3)% to 11.76(4)% (+0.52%) and to 11.44(2)% (+0.21%), respectively.

Four Dinuclear and One-Dimensional-Chain Dysprosium and Terbium Complexes Based on 2-Hydroxy-3-methoxybenzoic Acid: Structures, Fluorescence, Single-Molecule-Magnet, and Ab Initio Investigation

The unique electronic configurations of lanthanide(III) ions generate abundant electronic energy levels, resulting in the fantastic magnetic and optical multifunctional properties of lanthanide complexes. Here, 2-hydroxy-3-methoxybenzoic acid (H₂MBA) was used to construct four Dy(III) and Tb(III) complexes containing two isostructural dinuclear complexes of [Ln₂(HMBA)₂(MBA)₂(DMF)₂(H₂O)₂]·6H₂O [Ln = Dy (1), Tb (2); DMF = N,N-dimethylformamide] and two other isostructural beltlike one-dimensional-chain complexes of [NH₄][Ln(HMBA)₄] [Ln = Dy (3), Tb (4)]. Fluorescence measurements reveal that H₂MBA can sensitize Dy(III) and Tb(III) characteristic luminescence. Furthermore, complex 3 can emit white light under UV-light irradiation originating from a dichromatic mixture of a blue emission of H₂MBA and a dominating yellow emission of Dy³⁺ ions. Magnetic susceptibility measurements show that two Dy(III) complexes are single-molecule magnets with anisotropy barriers of 90(2) and 31(5) cm^-1 for 1 and 3, respectively. The magnet-luminescence-structure correlations as well as relaxation pathways are investigated by ab initio calculations and fluorescent spectrometry.

Solvatochromic dual luminescence of Eu–Au dyads decorated with chromophore phosphines

Chromophore-containing phosphines produce highly solvatochromic gold(i) fluorophores. Their combination with red-emitting Eu centers offers a facile approach to dual emissive complexes with widely tunable luminescence characteristics.

Understanding the near-infrared fluorescence and field-induced single-molecule-magnetic properties of dinuclear and one-dimensional-chain ytterbium complexes based on 2-hydroxy-3-methoxybenzoic acid

Two Yb(iii) complexes with a dinuclear and belt-like one-dimensional chain structure were reported. Their near-infrared luminescence and single-molecule magnetic properties were investigated in detail.

Photochromic and luminescent switchable iodoargentate hybrids directed by solvated lanthanide cations

A series of photochromic and luminescent switchable iodoargentate hybrids have been constructed by using solvated lanthanide cations as SDAs.

Neodymium β-diketonate showing slow magnetic relaxation and acting as a ratiometric thermometer based on near-infrared emission

Self-assembly of β-diketonate (Htta = thenoyl(trifluoro)acetone) and 4,4′-azopyridine (Azo-py) with neodymium(iii) ions in the presence of methanol resulted in the formation of mononuclear complex [Nd^III(TTA)₃(MeOH)₂]·0.5Azo-py (A) in which two asymmetric units are linked by Azo-py through hydrogen bonding via methanol. A reveals near-infrared emission (NIR) centred at about 895 and 1056 nm, in the 10–370 K temperature range, originating from the two emissive transitions on Nd(iii) from ⁴F_3/2 to ⁴I_9/2 and ⁴I_11/2 levels, respectively. Furthermore, the NIR luminescence intensity of A at room temperature augments two times upon thermal elimination of one coordinated methanol molecule. The thermally activated A exhibits single centre ratiometric thermometer behaviour in a wide temperature range from 10 to 300 K. Moreover, fluorescence properties of A were compared to another mononuclear complex [Nd^III(TTA)₃(4-OHpy)(H₂O)] (B). Assembly A also exhibits field-induced slow magnetic relaxation properties with an energy barrier of ΔE/k_B = 19.7(7) K and an attempt time of relaxation, τ₀ = 3.7(8) × 10⁻⁷ s for fresh sample A, and ΔE/k_B = 27.3 K and τ₀ = 8.5(0) × 10⁻⁸ for assembly A after thermal treatment at 370 K.

In this work, we investigated thermally-induced Nd-based one centred ratiometric thermometer which also exhibit single molecule magnetic properties.