New insights into structure and luminescence of Eu(III) and Sm(III) complexes of the 3,4,3-LI(1,2-HOPO) ligand

Lanthanide-Dependent Photochemical and Photophysical Properties of Lanthanide-Anthracene Complexes: Experimental and Theoretical Approaches

The structural, photophysical, and photochemical properties of Ln(depma)(hmpa)2(NO3)3 (Ln = La, Ce, Nd, Sm, Eu, Tb, Ho, Er, and Yb) complexes 1-Ln were investigated with a multidisciplinary approach involving synthesis, photocycloaddition-based crystal engineering, spectroscopic analytical techniques and quantum chemical ab initio calculations. Depending on the Ln3+ ion the isostructural 1-Ln complexes exhibit quite different behavior upon excitation at 350-400 nm. Some 1-Ln complexes (Ln = La, Ce, Sm, Tb, Yb) emit a broad and strong band near 533 nm arising from paired anthracene moieties, whereas others (Ln = Nd, Eu, Ho, Er) do not. 1-Eu is not emissive at all, whereas 1-Nd, 1-Ho, and 1-Er exhibit a Ln3+ based luminescence. Upon irradiation with 365 nm ultraviolet (UV) light 1-Ln (Ln = La, Ce, Sm, Tb, Yb) dimerize by means of a photochemically induced [4 + 4] cycloaddition of the anthracene moieties, whereas 1-Ln (Ln = Nd, Eu, Ho, Er) remain monomers. We propose three models, based on the matching of the energy levels between the Ln3+ ion and the paired or dimerized anthracene units in the energy-resonance crossing region, as well as on internal conversion-driven and intersystem crossing-driven energy transfer, which explain the Ln3+ ion regulated photophysics and photochemistry of the 1-Ln complexes.

Luminescence-Based Infrared Thermal Sensors: Comprehensive Insights

Recent chronological breakthroughs in materials innovation, their fabrication, and structural designs for disparate applications have paved transformational ways to subversively digitalize infrared (IR) thermal imaging sensors from traditional to smart. The noninvasive IR thermal imaging sensors are at the cutting edge of developments, exploiting the abilities of nanomaterials to acquire arbitrary, targeted, and tunable responses suitable for integration with host materials and devices, intimately disintegrate variegated signals from the target onto depiction without any discomfort, eliminating motional artifacts and collects precise physiological and physiochemical information in natural contexts. Highlighting several typical examples from recent literature, this review article summarizes an accessible, critical, and authoritative summary of an emerging class of advancement in the modalities of nano and micro-scale materials and devices, their fabrication designs and applications in infrared thermal sensors. Introduction is begun covering the importance of IR sensors, followed by a survey on sensing capabilities of various nano and micro structural materials, their design architects, and then culminating an overview of their diverse application swaths. The review concludes with a stimulating frontier debate on the opportunities, difficulties, and future approaches in the vibrant sector of infrared thermal imaging sensors.

Electron Paramagnetic Resonance, Electronic Ground State, and Electron Spin Relaxation of Seven Lanthanide Ions Bound to Lanmodulin and the Bioinspired Chelator, 3,4,3-LI(1,2-HOPO)

The electron paramagnetic resonance (EPR) spectra of lanthanide(III) ions besides Gd3+ , bound to small-molecule and protein chelators, are uncharacterized. Here, the EPR properties of 7 lanthanide(III) ions bound to the natural lanthanide-binding protein, lanmodulin (LanM), and the synthetic small-molecule chelator, 3,4,3-LI(1,2-HOPO) ("HOPO"), were systematically investigated. Echo-detected pulsed EPR spectra reveal intense signals from ions for which the normal continuous-wave first-derivative spectra are negligibly different from zero. Spectra of Kramers lanthanide ions Ce3+ , Nd3+ , Sm3+ , Er3+ , and Yb3+ , and non-Kramers Tb3+ and Tm3+ , bound to LanM are more similar to the ions in dilute aqueous:ethanol solution than to those coordinated with HOPO. Lanmodulins from two bacteria, with distinct metal-binding sites, had similar spectra for Tb3+ but different spectra for Nd3+ . Spin echo dephasing rates (1/Tm ) are faster for lanthanides than for most transition metals and limited detection of echoes to temperatures below ~6 to 12 K. Dephasing rates were environment dependent and decreased in the order water:ethanol>LanM>HOPO, which is attributed to decreasing librational motion. These results demonstrate that the EPR spectra and relaxation times of lanthanide(III) ions are sensitive to coordination environment, motivating wider application of these methods for characterization of both small-molecule and biomolecule interactions with lanthanides.

Sc-HOPO: A Potential Construct for Use in Radioscandium-Based Radiopharmaceuticals

Three isotopes of scandium─43Sc, 44Sc, and 47Sc─have attracted increasing attention as potential candidates for use in imaging and therapy, respectively, as well as for possible theranostic use as an elementally matched pair. Here, we present the octadentate chelator 3,4,3-(LI-1,2-HOPO) (or HOPO), an effective chelator for hard cations, as a potential ligand for use in radioscandium constructs with simple radiolabeling under mild conditions. HOPO forms a 1:1 Sc-HOPO complex that was fully characterized, both experimentally and theoretically. [47Sc]Sc-HOPO exhibited good stability in chemical and biological challenges over 7 days. In healthy mice, [43,47Sc]Sc-HOPO cleared the body rapidly with no signs of demetalation. HOPO is a strong candidate for use in radioscandium-based radiopharmaceuticals.

Metal-Ligand Interactions in Scandium Complexes with Radiopharmaceutical Applications

The radioisotopes of scandium (43Sc, 44Sc, and 47Sc) are potential candidates for use in imaging and therapy both separately and as elementally matched pairs for radiotheranostics. In the present study the bonding interactions of Sc3+ with 18 hepta- to decadentate ligands are compared using density functional theory (DFT) calculations. The bonding analysis is based on the natural bond orbital (NBO) model. The main contributions to the bonding were assessed using natural energy decomposition analysis (NEDA). Most of the ligands have anionic character (charges from 2- to 8-); thus the electrical term determines the major differences in the interaction energies. However, interesting features were found in the covalent contributions manifested by the ligand → Sc3+ charge transfer (CT) interactions. Significant differences could be observed in the energetic contributions of the N and O donors to the total CT.

Chelation Behaviors of 3,4,3-LI(1,2-HOPO) with Lanthanides and Actinides Implicated by Molecular Dynamics Simulations

The hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (denoted as t-HOPO) is a potential chelator agent for decorporation of in vivo actinides (An), while its coordination modes with actinides and the dynamics of the complexes (An(t-HOPO)) in aqueous phase remain unclear. Here, we report molecular dynamics simulations of the complexes with key actinides (Am³⁺, Cm³⁺, Th⁴⁺, U⁴⁺, Np⁴⁺, Pu⁴⁺) to study their coordination and dynamic behaviors. For comparison, the complexation of the ligand with a ferric ion and key lanthanides (Sm³⁺, Eu³⁺, Gd³⁺) was also studied. The simulations show that the nature of metal ions determines the properties of the complexes. The t-HOPO in the Fe^III(t-HOPO)^1- complex ion formed a compact and rigid cage to encapsulate the ferric ion, which was hexa-coordinated. Ln³⁺/An³⁺ cations were ennea-coordinated with eight ligating oxygen atoms from t-HOPO and one from an aqua ligand, and An⁴⁺ cations were deca-coordinated with a second aqua ligand. The t-HOPO shows strong affinity for metal ions (stronger for An⁴⁺ than Ln³⁺/An³⁺) benefited from its high denticity and its flexible backbone. Meanwhile, the complexes displayed different dynamic flexibilities, with the An^IV(t-HOPO) complexes more significant than the others, and in the An^IV(t-HOPO) complexes, the fluctuation of the t-HOPO ligand was highly correlated with that of the eight ligating O atoms. This is attributed to the more compact conformation of the ligand, which raises backbone tension, and the competition of the aqua ligand against the t-HOPO ligand in coordinating with the tetravalent actinides. This work enriches our understanding on the structures and conformational dynamics of the complexes of actinides with t-HOPO and is expected to benefit the design of HOPO analogues for actinide sequestering.

Magnet-Free Time-Resolved Magnetic Circular Dichroism with Pulsed Vector Beams

Magnetic circular dichroism (MCD) is a widely used spectroscopic technique which reveals valuable information about molecular geometry and electronic structure. However, the weak signal and the necessary strong magnets impose major limitations on its application. We propose a novel protocol to overcome these limitations by using pulsed vector beams (VBs), which consist of nanosecond gigahertz pump and femtosecond UV-vis probe pulses. By virtue of the strong longitudinal electromagnetic fields, the MCD signal detected by using the pulsed VBs is greatly enhanced compared to conventional MCD performed with plane waves. Furthermore, varying the pump-probe time delay allows monitoring the ultrafast variation of molecular properties.

Excited-State Dynamics of Crossing-Controlled Energy Transfer in Europium Complexes

Photosensitized energy transfer (EnT) phenomena occur frequently in a variety of photophysical and photochemical processes and have traditionally been treated with the donor-acceptor distance-dependent Förster and Dexter models. However, incorrect arguments and formulae were employed by ignoring energy resonance conditions and the selection rules of the state-to-state transition in special cases, especially for the sensitive intramolecular EnT of lanthanide complexes. Herein, we proposed an innovative model of energy-degeneracy-crossing-controlled EnT, which can be experimentally confirmed by time-resolved two-dimensional photoluminescence measurements. The computationally determined energy resonance region provides the most effective channel to achieve metal-to-ligand EnT beyond the distance-dependent model and sensitively bifurcates into symmetry-allowed or -forbidden channels for some representative europium antenna complexes. The outcomes of the multidisciplinary treatment contribute to a complementary EnT model that can be tuned by introducing a phosphorescence modulator and altering the antenna-related parameters of the ligand-centered energy level of the ³ππ* state and its spin-orbit coupling for the ³ππ* → S₀ ^* transition through mechanism-guided crystal engineering and should motivate further development of mechanistic models and applications.

Combining the Best of Two Chelating Titans: A Hydroxypyridinone-Decorated Macrocyclic Ligand for Efficient and Concomitant Complexation and Sensitized Luminescence of f-Elements

An ideal chelator for f-elements features rapid kinetics of complexation, high thermodynamic stability, and slow kinetics of dissociation. Here we present the facile synthesis of a macrocyclic ligand bearing four 1-hydroxy-2-pyridinone units linked to a cyclen scaffold that rapidly forms thermodynamically stable complexes with lanthanides (Sm³⁺ , Eu³⁺ , Tb³⁺ , Dy³⁺ ) and a representative late actinide (Cm³⁺ ) in aqueous media and concurrently sensitizes them. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed an increase in the Ln/An-O bond lengths following the trend Cm>Eu>Tb and EXAFS data were compatible with time-resolved luminescence studies, which indicated one to two water molecules in the inner metal coordination sphere of Eu(III) and two water molecules for the Cm(III) complex. Spectrofluorimetric ligand competition titrations against DTPA confirmed the high thermodynamic stability of DOTHOPO complexes, with pM values between 19.9(1) and 21.9(2).

Structural and spectroscopic characterization of an einsteinium complex

The transplutonium elements (atomic numbers 95-103) are a group of metals that lie at the edge of the periodic table. As a result, the patterns and trends used to predict and control the physics and chemistry for transition metals, main-group elements and lanthanides are less applicable to transplutonium elements. Furthermore, understanding the properties of these heavy elements has been restricted by their scarcity and radioactivity. This is especially true for einsteinium (Es), the heaviest element on the periodic table that can currently be generated in quantities sufficient to enable classical macroscale studies¹. Here we characterize a coordination complex of einsteinium, using less than 200 nanograms of ²⁵⁴Es (with half-life of 275.7(5) days), with an organic hydroxypyridinone-based chelating ligand. X-ray absorption spectroscopic and structural studies are used to determine the energy of the L₃-edge and a bond distance of einsteinium. Photophysical measurements show antenna sensitization of Es^III luminescence; they also reveal a hypsochromic shift on metal complexation, which had not previously been observed in lower-atomic-number actinide elements. These findings are indicative of an intermediate spin-orbit coupling scheme in which j-j coupling (whereby single-electron orbital angular momentum and spin are first coupled to form a total angular momentum, j) prevails over Russell-Saunders coupling. Together with previous actinide complexation studies², our results highlight the need to continue studying the unusual behaviour of the actinide elements, especially those that are scarce and short-lived.

Two-Photon Antenna Sensitization of Curium: Evidencing Metal-Driven Effects on Absorption Cross Section in f-Element Complexes

Two-photon-excited fluorescence spectroscopy is a powerful tool to study the structural and electronic properties of optically active complexes and molecules. Although numerous lanthanide complexes have been characterized by two-photon-excited fluorescence in solution, this report is the first to apply such a technique to actinide compounds. Contrasting with previous observations in lanthanides, we demonstrate that the two-photon absorption properties of the complexes significantly depend on the metal (4f vs 5f), with Cm(III) complexes showing significantly higher two-photon absorption cross sections than lanthanide analogues and up to 200-fold stronger emission intensities. These results are consistent with electronic and structural differences between the lanthanide and actinide systems studied. Hence, the described methodology can provide valuable insights into the interactions between f-elements and ligands, along with promising prospects on the characterization of scarce compounds.

Rapid Detection of Gadolinium-Based Contrast Agents in Urine with a Chelated Europium Luminescent Probe

Gadolinium-based contrast agents are widely used in magnetic resonance imaging procedures to enhance image contrast. Despite their ubiquitous use in clinical settings, gadolinium is not an innocuous element, as suggested by several disorders associated with its use. Therefore, novel analytical technologies capable of tracking contrast agent excretion through urine are necessary for optimizing patient safety after imaging procedures. Here, we describe an assay to detect and quantify contrast agents in urine based on the luminescence quenching of a metal chelate probe, Eu³⁺-3,4,3-LI(1,2-HOPO), which only requires 10 min incubation before measurement. Gadolinium-based contrast agents prevent the formation of the Eu³⁺-3,4,3-LI(1,2-HOPO) complex, subsequently decreasing the luminescence of the assay solution. Three commercial contrast agents, Magnevist, Multihance, and Omniscan, were used to demonstrate the analytical concept in synthetic human urine, and subsequent quantification of mouse urine samples. To the best of our knowledge, this is the first assay capable of detecting and quantifying gadolinium-based contrast agents in urine without sample preparation or digestion.

Developing scandium and yttrium coordination chemistry to advance theranostic radiopharmaceuticals

The octadentate siderophore analog 3,4,3-LI(1,2-HOPO), denoted 343-HOPO hereafter, is known to have high affinity for both trivalent and tetravalent lanthanide and actinide cations. Here we extend its coordination chemistry to the rare-earth cations Sc³⁺ and Y³⁺ and characterize fundamental metal-chelator binding interactions in solution via UV-Vis spectrophotometry, nuclear magnetic resonance spectroscopy, and spectrofluorimetric metal-competition titrations, as well as in the solid-state via single crystal X-ray diffraction. Sc³⁺ and Y³⁺ binding with 343-HOPO is found to be robust, with both high thermodynamic stability and fast room temperature radiolabeling, indicating that 343-HOPO is likely a promising chelator for in vivo applications with both metals. As a proof of concept, we prepared a ⁸⁶Y-343-HOPO complex for in vivo PET imaging, and the results presented herein highlight the potential of 343-HOPO chelated trivalent metal cations for therapeutic and theranostic applications.

Selective Lanthanide Sensing with Gold Nanoparticles and Hydroxypyridinone Chelators

The octadentate hydroxypyridinone chelator 3,4,3-LI(1,2-HOPO) is a promising therapeutic agent because of its high affinity for f-block elements and noncytotoxicity at medical dosages. The interaction between 3,4,3-LI(1,2-HOPO) and other biomedically relevant metals such as gold, however, has not been explored. Gold nanoparticles functionalized with chelators have demonstrated great potential in theranostics, yet thus far, no protocol that combines 3,4,3-LI(1,2-HOPO) and colloidal gold has been developed. Here, we characterize the solution thermodynamic properties of the complexes formed between 3,4,3-LI(1,2-HOPO) and Au³⁺ ions and demonstrate how under specific pH conditions the chelator promotes the growth of gold nanoparticles, acting as both reducing and stabilizing agent. 3,4,3-LI(1,2-HOPO) ligands on the nanoparticle surface remain active and selective toward f-block elements, as evidenced by gold nanoparticle selective aggregation. Finally, a new colorimetric assay capable of reaching the detection levels necessary for the quantification of lanthanides in waste from industrial processes is developed based on the inhibition of particle growth by lanthanides.

Series of Highly Luminescent Macrocyclic Sm(III) Complexes: Functional Group Modifications Together with Luminescence Performances in Solid-State, Solution, and Doped Poly(methylmethacrylate) Film

Here, we report our trials to regulate the luminescence performance of the macrocyclic samarium(III) complex and prepare four excellent luminescent Sm(III) complex-doped poly(methylmethacrylate) (PMMA) composites. Four 23-membered [1 + 1] Schiff-base macrocyclic mononuclear Sm(III) complexes, Sm-2 _a -Sm-2 _d , originating from dialdehydes with different pendant arms and 1,2-bis(2-aminoethoxy)ethane, have been constructed by the template method. Crystal structures reveal that every Sm(III) ion with the coordination geometry of a distorted bicapped square antiprism is capsulated by the macrocyclic cavity environment forming the "lasso-type" protection. Relative photophysical properties of macrocyclic Sm(III) complexes are carefully investigated in solid-state, methanol solution, and doped PMMA film, and all these show characteristic emissions of the Sm(III) ion associated with satisfactory lifetimes and quantum yields in all media, which could be comparable to reported outstanding examples. Especially, the luminescence performance for this type of Sm(III) complex could be regulated in the solid state by the use of different functional groups in the pendant arm while it is not achieved in solution and the doped PMMA composite. High emitting and air-stable plastic materials could be obtained when these Sm(III) complexes are doped in PMMA with 0.1 wt % mixing ratio, and the corresponding maximum lifetime and quantum yield are 61.2 μs and 0.63% in the case of complex Sm-2 _a , respectively. We believe that these highly luminescent "lasso-type" Sm(III) complexes and doped PMMA composites are valuable references in the design of luminescent lanthanide(III) hybrid materials.

Combinatorial design of multimeric chelating peptoids for selective metal coordination

The combinatorial synthesis of a new library of tetrameric peptoid ligands is introduced, enabling coordination and characterization of f-block metals.

Current methods for metal chelation are generally based on multidentate organic ligands, which are generated through cumbersome multistep synthetic processes that lack flexibility for systematically varying metal-binding motifs. Octadentate ligands incorporating hydroxypyridinone or catecholamide binding moieties onto a spermine scaffold are known to display some of the highest affinities towards f-elements. Enhancing binding affinity for specific lanthanide or actinide ions however, necessitates ligand architectures that allow for modular and high throughput synthesis. Here we introduce a high-throughput combinatorial library of 16 tetrameric N-substituted glycine oligomers (peptoids) containing hydroxypyridinone or catecholamide chelating units linked via an ethylenediamine bridge and, for comparison, we also synthesized the corresponding mixed ligands derived from the spermine scaffold: 3,4,3-LI(1,2-HOPO)₂(CAM)₂ and 3,4,3-LI(CAM)₂(1,2-HOPO)₂. Coordination-based luminescence studies were carried out with Eu³⁺ and Tb³⁺ to begin probing the properties of the new ligand architecture and revealed higher sensitization efficiency with the spermine scaffold as well as different spectroscopic features among the structural peptoid isomers. Solution thermodynamic properties of selected ligands revealed different coordination properties between the spermine and peptoid analogues with Eu³⁺ stability constants log β₁₁₀ ranging from 28.88 ± 3.45 to 43.97 ± 0.49. The general synthetic strategy presented here paves the way for precision design of new specific and versatile ligands, with a variety of applications tailored towards the use of f-elements, including separations, optical device optimization, and pharmaceutical development.

Breaking the 1,2-HOPO barrier with a cyclen backbone for more efficient sensitization of Eu(iii) luminescence and unprecedented two-photon excitation properties

A cyclen backbone was utilized to study the effect of backbone rigidity on Eu(iii) luminescence sensitization using a 1,2-HOPO derivative and 2-thenoyltrifluoroacetonate (TTA) as chromophores. The restriction of molecular movement of Eu-Cy-HOPO brought about by the increased rigidity provided a tightly packed coordination environment for the octadentate Eu(iii) center which resulted in the highest overall quantum yield (30.2%) and sensitization efficiency (64.6%) among 1,2-HOPO sensitized Eu(iii) complexes. Eu-Cy-HOPO is also the first 1,2-HOPO-based lanthanide complex to emit Eu(iii) luminescence under two-photon excitation.

Inducing selectivity and chirality in group IV metal coordination with high-denticity hydroxypyridinones

The solution- and solid-state interactions between the octadentate siderophore mimic 3,4,3-LI(1,2-HOPO) (343HOPO) and group IV metal ions were investigated using high-resolution mass spectrometry, liquid chromatography, UV-visible spectrophotometry, metal-competition batch titrations, and single crystal X-ray diffraction. 343HOPO forms a neutral 1 : 1 complex, [HfIV343HOPO], that exhibits extreme stability in aqueous solution, with a log β110 value reaching 42.3. These results affirm the remarkable charge-based selectivity of 343HOPO for octacoordinated tetravalent cations with a Hf(iv) complex 1021 more stable than its Lu(iii) analogue. Moreover, [HfIV343HOPO] and its Zr(iv) counterpart show exceptional robustness, with the ligand remaining bound to the cation over a very broad pH range: from pH ∼ 11 to acidic conditions as strong as 10 M HCl. In stark contrast, Ti(iv)-343HOPO species are far less stable and undergo hydrolysis at pH as low as ∼6, likely due to the mismatch between the preferred hexacoordinated Ti(iv) ion and octadentate 343HOPO ligand. The extreme charge-based and denticity-driven selectivity of 343HOPO, now observed across the periodic table, paves the way for new selective sequestration systems for radionuclides including medical 44Ti, 89Zr or 177Lu/Hf isotopes, toxic polonium (Po) contaminants, as well as rutherfordium (Rf) research isotopes. Furthermore, despite the lack of a chiral center in 343HOPO, its complexes with metal ions are chiral and appear to form a single set of enantiomers.

An excellent colorimetric and “turn off” fluorescent probe for tetrahydrofuran based on a luminescent macrocyclic samarium(iii) complex

We designed and prepared a macrocyclic samarium(iii) complex which served as an excellent colorimetric and “turn-off” fluorescent probe for sensing tetrahydrofuran.

An efficient approach to modulate the coordination number of yttrium ions for diverse network formation

Hidden role of water! It acts as a key to determine the coordination number of yttrium by controlling the active ligand concentration.

Ultrahigh luminescence quantum yield lanthanide coordination polymer as a multifunctional sensor

The investigation and development of advanced multifunctional and sensitive sensors with high luminescent quantum yield and the capability of detecting different analytes, such as metal ions, is imperative. Due to its inherent properties the lanthanide coordination complex is one candidate for sensing applications, particularly for multifunctional sensors. Herein, we present two series of alkali ion decorated lanthanide coordination polymers (Ln-CPs), which show ultrahigh luminescence quantum yields (QYs) of 77% (1a) and 92% (2a). To the best of our knowledge, 1a represents the first trifunctional lanthanide complex sensor that can simultaneous detect and discriminate three different analytes, namely H+/Cd2+/Cr3+ through a multimode optical response. Furthermore, the limit of detection (LOD) for Cr3+ is an ultralow value of 2.0 × 10-9 M with a sensing time of 2 h, which is comparable to the most sensitive Cr3+ chemosensor. More interestingly, 92% (2a) is an unprecedented luminescence QY among the reported lanthanide coordination complexes.

The coordination chemistry of lanthanide and actinide metal ions with hydroxypyridinone-based decorporation agents: orbital and density based analyses

In the context of the mitigation of the biological effects of internal radionuclide contamination and for efficient decorporation, the design and development of efficient chelators for lanthanide and actinide metal ions has become a central issue. The pioneering work of Raymond and coworkers (Chem. Rev., 2003, 103, 4207-4282) led to the development of siderophore-related hydroxypyridinonate ligands for possible treatment of internalized radionuclides. However, the structure-function relationship of Ln/An bound to these ligands, particularly the bonding and coordination aspects are not clearly understood at the atomic level. Here, we have investigated the structure, binding and energetics of trivalent and tetravalent Ln/An (Sm3+, Eu3+, Am3+, Cm3+, Th4+, Pu4+) ions with spermine-based octadentate hydroxypyridinonate chelators, namely 3,4,3-LI(1,2-HOPO) and its 3,3,3 variant, using relativistic density functional theory (DFT). Furthermore, we have performed orbital and density based analyses to elucidate the nature of bonding in these complexes. In accordance with the experimental stability constant, we found the maximum binding free energy for An4+ (Pu4+, Th4+) as compared to trivalent metal ions. CDA and ECDA analyses along with orbital-based population analyses confirmed the higher ligand to metal charge transfer for An4+ than for trivalent metal ions. Furthermore, the aromaticity index analysis suggested the presence of crucial chelatoaromatic stabilization for all these metal ions with the maximum for An4+. QTAIM descriptors indicated that the binding of An/Ln with the hard oxygen donor of the ligands is of the donor-acceptor type but a higher degree of covalency exists for actinides as compared to lanthanides. Furthermore, QTAIM and molecular orbital analysis confirmed that such covalency is of the energy-driven type and strictly originates from the orbital mixing event of An-5f orbitals with the ligand orbitals.

Chiral BINAPO-Controlled Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Triple-Stranded Europium(III) Podates

Chiral lanthanide helical architectures have received intense attentions in recent years because of their potential applications as chiral probes and sensors and as circularly polarized luminescence (CPL) materials. However, stereoselectivity control in the self-assembly of lanthanide helicate is challenging due to the poor stereochemical preference and variable coordination numbers of Ln(III) ions. Herein, we reported the employing chiral ancillary ligand R/S-BINAPO to induce achiral tripodal ligand to form a pair of homochiral lanthanide triple-helical podates [Eu(TTEA)((R/S)-BINAPO); R/S-1] {(R/S)-BINAPO = ( R/ S)-2,2'-bis(diphenylphosphoryl)-1,1'-binaphthyl; TTEA = tris[(4-(4,4,4-trifluoro-1,3-dioxobutyl)-benzamido)ethyl]amine}. X-ray crystallographic analysis for rac-1 reveals that the chirality of BINAPO is transferred during the self-assembly process to give either P or M helical architectures in podates. The ¹H and ³¹P NMR and circular dichroism measurements confirm the diastereopurity of the assemblies in solution. A detailed optical and chiroptical characterization reveals that the luminescent enantiopure podates not only exhibit intense CPL with | g_lum| values reaching 0.072 but also show high luminescence quantum yields of 32.8%. Our results provide a feasible strategy for designing homochiral helical lanthanide supramolecular architecture and synthesizing excellent CPL materials.

Correlation of Structural and Magnetic Properties in a Set of Mononuclear Lanthanide Complexes

The electronic and magnetic properties of a set of mononuclear terbium(III) and dysprosium(III) complexes with two tetradentate 1-hydroxy-pyridin-2-one (1,2-HOPO) ligands are reported. Two primary coordination geometries are observed, depending on the length of the linker between the 1,2-HOPO donor moieties and the resulting arrangements of the linker. Fine details of the magnetic circular dichroism (MCD) spectra of the dysprosium(III) complexes illustrate differences in the splitting of the J multiplets and allow for a thorough ligand field analysis. High frequency electron paramagnetic resonance (HF-EPR) studies of the terbium(III) complexes give insight into the composition of the ground states. Ab initio calculations are utilized to rationalize the experimental results and further illustrate the effect of the structural features on the electronic and magnetic properties of the different complexes.

Intramolecular sensitization of americium luminescence in solution: shining light on short-lived forbidden 5f transitions

The photophysical properties and solution thermodynamics of water soluble trivalent americium (Am(III)) complexes formed with multidentate chromophore-bearing ligands, 3,4,3-LI(1,2-HOPO), Enterobactin, and 5-LIO(Me-3,2-HOPO), were investigated. The three chelators were shown to act as antenna chromophores for Am(III), generating sensitized luminescence emission from the metal upon complexation, with very short lifetimes ranging from 33 to 42 ns and low luminescence quantum yields (10(-3) to 10(-2)%), characteristic of Near Infra-Red emitters in similar systems. The specific emission peak of Am(III) assigned to the (5)D1 → (7)F1 f-f transition was exploited to characterize the high proton-independent stability of the complex formed with the most efficient sensitizer 3,4,3-LI(1,2-HOPO), with a log β110 = 20.4 ± 0.2 value. In addition, the optical and solution thermodynamic features of these Am(III) complexes, combined with density functional theory calculations, were used to probe the influence of electronic structure on coordination properties across the f-element series and to gain insight into ligand field effects.

Toxic heavy metal – Pb, Cd, Sn – complexation by the octadentate hydroxypyridinonate ligand archetype 3,4,3-LI(1,2-HOPO)

The toxicity of heavy metals such as lead (Pb), cadmium (Cd) and tin (Sn) has long been known but accidental exposures of large populations to these elements remain unfortunately a topical issue.

Photophysics of Coumarin and Carbostyril-Sensitized Luminescent Lanthanide Complexes: Implications for Complex Design in Multiplex Detection

Luminescent lanthanide (Ln(III)) complexes with coumarin or carbostyril antennae were synthesized and their photophysical properties evaluated using steady-state and time-resolved UV-vis spectroscopy. Ligands bearing distant hydroxycoumarin-derived antennae attached through triazole linkers were modest sensitizers for Eu(III) and Tb(III), whereas ligands with 7-amidocarbostyrils directly linked to the coordination site could reach good quantum yields for multiple Ln(III), including the visible emitters Sm(III) and Dy(III), and the near-infrared emitters Nd(III) and Yb(III). The highest lanthanide-centered luminescence quantum yields were 35% (Tb), 7.9% (Eu), 0.67% (Dy), and 0.18% (Sm). Antennae providing similar luminescence intensities with 2-4 Ln-emitters were identified. Photoredox quenching of the carbostyril antenna excited states was observed for all Eu(III)-complexes and should be sensitizing in the case of Yb(III); the scope of the process extends to Ln(III) for which it has not been seen previously, specifically Dy(III) and Sm(III). The proposed process is supported by photophysical and electrochemical data. A FRET-type mechanism was identified in architectures with both distant and close antennae for all of the Lns. This mechanism seems to be the only sensitizing one at long distance and probably contributes to the sensitization at shorter distances along with the triplet pathway. The complexes were nontoxic to either bacterial or mammalian cells. Complexes of an ester-functionalized ligand were taken up by bacteria in a concentration-dependent manner. Our results suggest that the effects of FRET and photoredox quenching should be taken into consideration when designing luminescent Ln complexes. These results also establish these Ln(III)-complexes for multiplex detection beyond the available two-color systems.

A luminescent lanthanide approach towards direct visualization of primary cilia in living cells

A simple and direct imaging tool (HGEu001) for primary cilia based on long-lived europium luminescence is firstly presented.

Sonochemical synthesis of a new nano-sized cerium(III) supramolecular compound; Precursor for nanoceria

Using a sonochemical method, nanoparticles of a new Ce(III) supramolecular compound, (NAMH(+))2[Ce4(pydc)6(pydcH)2(H2O)8]·8H2O (1), (H2pydc=2,6-pyridinedicarboxylic acid, NAM=nicotinamide), have been synthesized. Compound 1 was characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), FT-IR spectroscopy and elemental analyses, and its structure was determined by X-ray crystallography. It has been revealed that its structure consists of tetra-nuclear building units that extend to a 3D supramolecular network via non-covalent interactions mainly hydrogen bonding. The thermal stability of complex 1 both for its crystals and nanostructures has been studied by the thermal gravimetric (TG) method and compared with each other. The role of ultrasound irradiation power and the concentration of initial reactants on the size and morphology of the nano-structured complex 1, has been investigated. Ceria nanoparticles were obtained upon the calcination of complex 1 at 800°C under atmospheric air. Furthermore, the fluorescent properties of complex 1 at room temperature were studied.

Hyper-stable organo-Eu(III) luminophore under high temperature for photo-industrial application

Novel organo-Eu(III) luminophores, Eu(hfa)x(CPO)y and Eu(hfa)x(TCPO)y (hfa: hexafluoroacetylacetonate, CPO: 4-carboxyphenyl diphenyl phosphine oxide, TCPO: 4,4',4″-tricarboxyphenyl phosphine oxide), were synthesized by the complexation of Eu(III) ions with hfa moieties and CPO or TCPO ligands. The thermal and luminescent stabilities of the luminophores are extremely high. The decomposition temperature of Eu(hfa)x(CPO)y and Eu(hfa)x(TCPO)y were determined as 200 and 450 °C, respectively. The luminescence of Eu(hfa)x(TCPO)y under UV light irradiation was observed even at a high temperature, 400 °C. The luminescent properties of Eu(hfa)x(CPO)y and Eu(hfa)x(TCPO)y were estimated from emission spectra, quantum yields and lifetime measurements. The energy transfer efficiency from hfa moieties to Eu(III) ions in Eu(hfa)x(TCPO)y was 59%. The photosensitized luminescence of hyper-stable Eu(hfa)x(TCPO)y at 400 °C is demonstrated for future photonic applications.