Circularly Polarized Luminescence of Silica-Grafted Europium Chiral Derivatives Prepared through a Sequential Functionalization

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.

Competing excitation paths in luminescent heterobimetallic Ln-Al complexes: Unraveling interactions via experimental and theoretical investigations

The interest for heterometallic lanthanide-d or-p metal (Ln-M) complexes is growing because of a potential cooperative or synergistic effect related to the proximity of two different metals in the same molecular architecture affording special tunable physical properties. To exploit the potentiality of Ln-M complexes, suitable synthetic approaches, and the in-depth understanding of the effect of each building block on their properties are mandatory. Here, we report the study on a family of heterometallic luminescent complexes [Ln(hfac)₃Al(L)₃], Ln= Eu³⁺ and Tb³⁺. Using different L ligands, we investigated the effect of the steric and electronic properties of the Al(L)₃ fragment, highlighting the general validity of the employed synthetic route. A marked difference in the light emission of [Eu(hfac)₃Al(L)₃] and [Tb(hfac)₃Al(L)₃] complexes has been observed. Thanks to photoluminescence experiments and Density Functional Theory calculations, Ln³⁺ emissions are explained with a model involving two non-interacting excitation paths through hfac or Al(L)₃ ligands.

Circularly Polarized Luminescent Chiral Photonic Films Based on the Coassembly of Cellulose Nanocrystals and Gold Nanoclusters

In this work, we studied the formation and properties of composite films coassembled by cellulose nanocrystals (CNCs) and bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs). The influences of the BSA-AuNC concentration on the structure and optical properties of CNC-based composite films were further studied. It was found that the composite film retained the chiral nematic structure and optical activity. The self-assembled CNC and BSA-AuNC helical superstructures can produce strong, left-handed, circularly polarized luminescence with dissymmetry factors up to 0.287. Meanwhile, the third component, polyethylene glycol, was introduced without affecting the structural color and fluorescence characteristics of the composite film to enhance the flexibility of the film. The simplicity of the film preparation, the abundance of CNCs, and the flexibility and stability of the composite films pave the way for the production of functional materials with integrated functions.

Diastereoselective self-assembly of a triple-stranded europium helicate with light modulated chiroptical properties

Chiroptical photoswitches are of increasing interest for their potential in advanced information technologies. Herein, an achiral bis-β-diketonate ligand (o-L) with a photoresponsive diarylethene moiety as a linker was designed, which co-assembled with Eu³⁺ ions and R- and S-bis(diphenylphosphoryl)-1,10-binaphthyl (R/S-BINAPO) as chiral ancillaries to form dinuclear triple-stranded helicates, [Eu₂(o-L)₃(R/S-BINAPO)₂]. The helicates in the enantiopure form were confirmed by ¹H, ¹⁹F, ³¹P NMR and DOSY NMR analyses. Furthermore, the mirror-image CD and CPL spectra also demonstrate the existence of stable ground- and excited-state chiralities in solution. When exposed to alternate ultraviolet and visible light, the helicates showed reversible color variations from colorless to purple, followed by the presence of light-triggered quadruple optical and chiroptical outputs, named CD, PL, CPL and g_lum switches. With these light-modulated optical outputs, the possibility for the fabrication of IMPLICATION and INHIBIT logic gates was discussed.

Understanding Selectivity of Mesoporous Silica-Grafted Diglycolamide-Type Ligands in the Solid-Phase Extraction of Rare Earths

Rare earth elements (REEs) and their compounds are essential for rapidly developing modern technologies. These materials are especially critical in the area of green/sustainable energy; however, only very high-purity fractions are appropriate for these applications. Yet, achieving efficient REE separation and purification in an economically and environmentally effective way remains a challenge. Moreover, current extraction technologies often generate large amounts of undesirable wastes. In that perspective, the development of selective, reusable, and extremely efficient sorbents is needed. Among numerous ligands used in the liquid-liquid extraction (LLE) process, the diglycolamide-based (DGA) ligands play a leading role. Although these ligands display notable extraction performance in the liquid phase, their extractive chemistry is not widely studied when such ligands are tethered to a solid support. A detailed understanding of the relationship between chemical structure and function (i.e., extraction selectivity) at the molecular level is still missing although it is a key factor for the development of advanced sorbents with tailored selectivity. Herein, a series of functionalized mesoporous silica (KIT-6) solid phases were investigated as sorbents for the selective extraction of REEs. To better understand the extraction behavior of these sorbents, different spectroscopic techniques (solid-state NMR, X-ray photoelectron spectroscopy, XPS, and Fourier transform infrared spectroscopy, FT-IR) were implemented. The obtained spectroscopic results provide useful insights into the chemical environment and reactivity of the chelating ligand anchored on the KIT-6 support. Furthermore, it can be suggested that depending on the extracted metal and/or structure of the ligand and its attachment to KIT-6, different functional groups (i.e., C═O, N-H, or silanols) act as the main adsorption centers and preferentially capture targeted elements, which in turn may be associated with the different selectivity of the synthesized sorbents. Thus, by determining how metals interact with different supports, we aim to better understand the solid-phase extraction process of hybrid (organo)silica sorbents and design better extraction materials.

Recent Advances in the Chemistry of Metal Carbamates

Following a related review dating back to 2003, the present review discusses in detail the various synthetic, structural and reactivity aspects of metal species containing one or more carbamato ligands, representing a large family of compounds across all the periodic table. A preliminary overview is provided on the reactivity of carbon dioxide with amines, and emphasis is given to recent findings concerning applications in various fields.

Electronic strain effect on Eu(iii) complexes for enhanced circularly polarized luminescence

The structural and electronic strain of ligands promotes the enhancement of the magnitude of circularly polarized luminescence in chiral Eu(iii) complexes.

Near-infrared emissive Er(iii) and Yb(iii) molecular nanomagnets in metal–organic chains functionalized by octacyanidometallates(iv)

Photoluminescent single-molecule magnets are formed in lanthanide(pyrazine N,N′-dioxide) chains with octacyanidometallate(iv) coordination branches playing a crucial role in sensitized NIR emission.

Near-infrared circularly polarized luminescence from chiral Yb(iii)-diketonates

We report a rare example of near infrared circularly polarized luminescence (NIR-CPL) in the 920–1050 nm region associated with the f–f transitions of Yb diketonate complexes bearing chiral ancillary ligands.

Unprecedented three-dimensional hydrogen-bonded hex topological chiral lanthanide–organic frameworks built from an achiral ligand

The design and preparation of chiral metal–organic frameworks (CMOFs) from achiral ligands are a big challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new linker, a total of eight chiral lanthanide–organic frameworks (LOFs), namely poly[diaquatris[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ2 O:O′]lanthanide(III)], L- and D-[Ln(C12H7N2O4)3(H2O)2] n [(1), Ln = Eu; (2), Ln = Gd; (3), Ln = Dy; (4), Ln = Tb], were hydrothermally synthesized without chiral reagents and determined by X-ray crystallography. Crystal structure analyses show that L-(1)–(4) crystallize in the hexagonal P65 space group and are isomorphous and isostructural, while the enantiomers D-(1)–(4) crystallize in the hexagonal P61 space group. All LnIII ions are octacoordinated by six carboxyl O atoms of six 3-nitro-4-(pyridin-4-yl)benzoate ligands and two water molecules in a dodecahedral geometry. A one-dimensional neutral helical [Ln2(CO2)3] n chain is observed in (1)–(4) as a chiral origin. These helical chains are further interconnected via directional hydrogen-bonding interactions between pyridyl groups and water molecules to construct a three-dimensional (3D) homochiral network with hex topology. The present CMOF structure is the first chiral 3D hydrogen-bonded hex-net and shows good water stability. Solid-state circular dichroism (CD) signals revealed that (1)–(4) crystallized through spontaneous resolution. Furthermore, (1) and (4) display a strong red and green photoluminescence at room temperature, respectively, but their intensities reduce to almost half at 200 °C. Notably, upon excitation under visible light (463 nm), a circularly polarized luminescence (CPL) of (1) in the solid state is observed for the first time, with a g lum value of 2.61 × 10−2.

Chiroptical methods in a wide wavelength range for obtaining Ln3+ complexes with circularly polarized luminescence of practical interest

We studied enantiopure chiral trivalent lanthanide (Ln3+ = La3+, Sm3+, Eu3+, Gd3+, Tm3+, and Yb3+) complexes with two fluorinated achiral tris(β-diketonate) ligands (HFA = hexafluoroacetylacetonate and TTA = 2-thenoyltrifluoroacetonate), incorporating a chiral bis(oxazolinyl)pyridine (PyBox) unit as a neutral ancillary ligand, by the combined use of optical and chiroptical methods, ranging from UV to IR both in absorption and circular dichroism (CD), and including circularly polarized luminescence (CPL). Ultimately, all the spectroscopic information is integrated into a total and a chiroptical super-spectrum, which allows one to characterize a multidimensional chemical space, spanned by the different Ln3+ ions, the acidity and steric demand of the diketone and the chirality of the PyBox ligand. In all cases, the Ln3+ ions endow the systems with peculiar chiroptical properties, either allied to f-f transitions or induced by the metal onto the ligand. In more detail, we found that Sm3+ complexes display interesting CPL features, which partly superimpose and partly integrate the more common Eu3+ properties. Especially, in the context of security tags, the pair Sm/Eu may be a winning choice for chiroptical barcoding.

Easy but not straightforward: base and solvent effect on the synthesis of luminescent europium 1,3-di(thien-2-yl)propane-1,3-dionate coordination complexes

Reaction between EuCl3 and the ligand 1,3-di(thien-2-yl)propane-1,3-dione (L) leads to luminescent coordination compounds [EuL3(EtOH)2] (1), [EuL2(i-PrOH)4]Cl (2) and [EuL3(i-PrOH)2] (3), isolated as single crystals in high yield (70%–95%). The Eu/β-diketonate ratio is tuned from 1:2 to 1:3 through the variation of the alcoholic solvent (ethanol and isopropanol) or the base (pyridine and NaOH). In all compounds, Eu3+ ions are eight-coordinated, and in 2, the molecules are arranged in an H-bond supported supramolecular 1D chain. These compositional and structural differences are reflected also on the absorption and emission properties.