Charge transfer excited states sensitization of lanthanide emitting from the visible to the near-infra-red

Lanthanide(III)-dependent hydration of the methanol dehydrogenase cofactor, pyrroloquinoline quinone

The mechanism by which pyrroloquinoline quinone (PQQ)-dependent methanol dehydrogenases (MDH), bearing either a Ca2+ or a lanthanide (Ln3+) ion in their active site, oxidize methanol has been intensely debated. In particular, the Ln3+-dependent activity of Ln-MDH remains poorly understood. The lack of experimental evidence represents a significant limitation to improve our understanding of these enzymes. In this work, we propose that insights on Ca- and Ln-MDH reactivity can be gained by examining a model reaction, the hydration of PQQ. Indeed, this reaction is similar to the first step of the putative methanol addition-elimination mechanism and is expected to be similarly influenced by the metal ion. The apparent affinity constants of PQQ for Ca2+ and Ln3+ were determined by UVvis absorption spectroscopy. Ln-PQQ complexes in aqueous solution were analyzed by steady-state and time-resolved fluorescence spectroscopy. The thermodynamic and kinetic parameters describing the equilibrium were obtained by variable-temperature and proton exchange spectroscopy (EXSY) NMR, as well as DFT calculations. Results demonstrated a Ln-dependent exchange rate for PQQ hydration equilibrium, the late and more Lewis acidic Ln3+ having the stronger impact.

Chemical Energy Lights Up Europium-Based Ultra-bright Afterglow for Bioanalysis Application

Photochemical afterglow materials are gaining great attention for the property to continuously emit light after the excitation source is removed. However, their limited luminescence quantum yield (QY) and brightness hinder the use in biological applications. In this study, we introduce a novel photochemical afterglow system that combines a newly designed photoenergy cache unit (PCU) with an emitter through coordination covalent bonds. The PCU boasts a dark state to significantly emit photons only through chemiexcitation in the process of photochemical reactions, facilitating direct energy transfer to the emitter and resulting in bright afterglow. The related mechanisms further guided us to achieve the highest reported afterglow luminescence quantum yield of 27.5 %. The system can be encapsulated and dispersed in aqueous solutions for in vivo bioimaging in living mice under mild and simple conditions (low concentration, low excitation power, short excitation time, short exposure time), and also for in vitro diagnostic through lateral flow immunoassay, enabling the highly sensitive detection of the inflammatory biomarker serum amyloid A (SAA) and demonstrating excellent correlation with clinical test results. This study offers new insights into enhancing luminescence QY and brightness of afterglow, highlighting the potential of such systems for further biomedical applications.

Luminescent Lanthanides in Biorelated Applications: From Molecules to Nanoparticles and Diagnostic Probes to Therapeutics

Lanthanides are particularly effective in their clinical applications in magnetic resonance imaging and diagnostic assays. They have open-shell 4f electrons that give rise to characteristic narrow, line-like emission which is unique from other fluorescent probes in biological systems. Lanthanide luminescence signal offers selection of detection pathways based on the choice of the ion from the visible to the near-infrared with long luminescence lifetimes that lend themselves to time-resolved measurements for optical multiplexing detection schemes and novel bioimaging applications. The delivery of lanthanide agents in cells allows localized bioresponsive activity for novel therapies. Detection in the near-infrared region of the spectrum coupled with technological advances in microscopies opens new avenues for deep-tissue imaging and surgical interventions. This review focuses on the different ways in which lanthanide luminescence can be exploited in nucleic acid and enzyme detection, anion recognition, cellular imaging, tissue imaging, and photoinduced therapeutic applications. We have focused on the hierarchy of designs that include luminescent lanthanides as probes in biology considering coordination complexes, multimetallic lanthanide systems to metal-organic frameworks and nanoparticles highlighting the different strategies in downshifting, and upconversion revealing some of the opportunities and challenges that offer potential for further development in the field.

A Set of Three GdIII Spin Labels with Methanethiosulfonyl Groups for Bioconjugation Covering a Wide Range of EPR Line Widths

Spin labels based on GdIII complexes are important tools for the elucidation of the structure, dynamics and interaction of biomolecules by electron paramagnetic resonance (EPR) spectroscopy. Their EPR spectroscopic properties line width and relaxation times influence their performance in a particular application. To be able to apply a complex well-suited for a specific application, a set of GdIII complexes with different EPR spectroscopic properties ready-made for spin labeling will be highly useful. We prepared three GdIII complexes with DO3APic, NO3Pic, and PyMTA as the basic ligand units. They cover a wide range of EPR line widths but have in common a cysteine-targeting methanethiosulfonyl (MTS) group connected to a pyridine ring, which is an intrinsic part of the ligand. The reaction with a cysteine-containing pentapeptide (0.45 mM in the peptide, pH ∼ 7) was complete within 90 s and chemoselective. The MTS group hydrolyzed with half-lives of >24, 8, 2, and 1 h at pH 5, 6, 7, and 8, respectively. The structurally related nicotinic acid-substituted disulfide (NDS) group was found to be hydrolytically much more stable. However, the MTS spin label clearly won the competition for the pentapeptide over the NDS spin label. If high reactivity is essential, MTS is clearly the better choice.

Bifunctional heterobimetallic 3d-4f [Co(II)-RE, RE = Dy, Eu, and Y] ionic complexes: modulation of the magnetic-luminescence behaviour

This work reports the engineering and functional properties of an emerging class of heterobimetallic 3d-4f ionic complexes designed with cobalt and rare-earth (RE) metals. We present a comprehensive examination of the structural, magnetic, optical, and thermal properties of the heterobimetallic ionic complexes with the general formula [Co(hfa)3]-[RE(hfa)2tetraglyme]+ (RE = Dy, Eu, and Y), where the metal centres are coordinated by hexafluoroacetylacetonate (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), β-diketone and tetraglyme (2,5,8,11,14-pentaoxapentadecane) polyether. Structural analysis reveals an octahedral coordination geometry enveloping the cobalt(II) centre, characterized by inherent symmetry properties consistent across the derivatives, while a capped square-antiprism coordination polyhedron is observed for the RE ions. Electron paramagnetic resonance (EPR) spectroscopy confirms the constancy of the electronic structure of the cobalt(II) moiety and the significant contribution of the lanthanide ions to the magnetic properties of the compounds. The non-trivial single-ion magnetic properties of cobalt(II), dysprosium(III), and europium(III) centres, and the effect of their interactions are investigated by a detailed static and dynamic magnetic susceptibility study. Moreover, optical analyses have been carried out showing the π-π* intraligand (IL) transition of the β-diketonate ligand and the d-d cobalt(II) transitions. Luminescence characterization of dysprosium(III) and europium(III) derivatives exhibits their characteristic emission bands, indicative of the unique photophysical properties conferred by the lanthanide ions. Thermal studies using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveal good thermal stability and volatility properties, underscoring the interesting nature of these ionic complexes for potential deposition on suitable substrates. In summary, these heterobimetallic complexes show intriguing optical and magnetic properties with potential implications across diverse scientific disciplines, including molecular magnetism, optoelectronics, and materials science.

The Many Facets of RuII(dppe)2 Acetylide Compounds

In this contribution, we describe the various research domains in which RuII alkynyl derivatives are involved. Their peculiar molecular properties stem from a strong and intimate overlap between the metal centered d orbitals and the π system of the acetylide ligands, resulting in plethora of fascinating properties such as strong and tunable visible light absorption with a strong MLCT character essential for sensing, photovoltaics, light-harvesting applications or non-linear optical properties. Likewise, the d/π mixing results in tunable redox properties at low potential due to the raising of the HOMO level, and making those compounds particularly suited to achieve redox switching of various properties associated to the acetylide conjugated ligand, such as photochromism, luminescence or magnetism, for charge transport at the molecular level and in field effect transistor devices, or charge storage for memory devices. Altogether, we show in this review the potential of RuII acetylide compounds, insisting on the molecular design and suggesting further research developments for this class of organometallic dyes, including supramolecular chemistry.

Specific smart sensing of electron-rich antibiotics or histidine improves the antenna effect, luminescence, and photodynamic sterilization capabilities of lanthanide polyoxometalates

Excessive discharge of antibiotics seriously threatens human health and is thus a global public health problem. This highlights the urgent need to develop intelligent sensing materials for specific antibiotics that are highly visual, fast, convenient, and inexpensive. Herein, two reverse α-octamolybdate polyoxometalates (POMs; Mo8) were used to chelate lanthanide ions to obtain lanthanide POMs (LnPOMs; LnMo16; Ln = Eu, Sm, Tb, Gd) with highly sensitive smart photoresponses to specific antibiotics (ofloxacin [OFN], norfloxacin [NOR], enrofloxacin [ENR], and oxytetracycline [OTC]) and histidine (His) with luminescence turn-on. Specific antibiotics and His, which has an electron-rich structure, can efficiently enhance the antenna effect, thereby greatly improving the luminescence of EuMo16. Surprisingly, OFN and NOR both enhanced the luminescence of Eu(III) ions and Mo8, whereas ENR and OTC only enhanced the luminescence of Eu(III) ions, showing a differentiated sensitization effect. More notably, the combination of POMs and Ln(III) ions enhanced the ability of LnPOMs to produce reactive oxygen species under light irradiation, and these LnPOMs showed significant sterilization effects on Escherichia coli and Staphylococcus aureus. To our knowledge, this is the first time electron-rich antibiotics or amino acids were used to enhance the luminescence of LnPOMs, achieving luminescence-enhanced photoresponse to specific antibiotics and amino acids.

Unearthing the Real-Time Excited State Dynamics from Antenna to Rare Earth Ions Using Ultrafast Transient Absorption

The conventional energy transfer pathway in organic lanthanide complexes is purported to be from the excited singlet state of the chromophore to the triplet state and subsequently directly to the emitting state of the trivalent lanthanide ion. In this work, we found that the energy transfer occurs from the triplet state to the nearest energy level, instead of directly to the emitting state of the lanthanide ion. The triplet decay rate for different lanthanide ions follows an energy gap law from the triplet level to the receiving level of the lanthanide ion. Three different categories of complexes were synthesized and inspected using different techniques, demonstrating the universality of our findings. This work renews the insights to conventional findings, highlighting the importance of the energy gap between the triplet state and the nearest lanthanide energy level in optimization of light harvesting. The rationale of ligand design of chromophores should be reconsidered, leading to various applications of lanthanide complexes with enhanced quantum yield and brightness.

Energy exchange between Nd3+ and Er3+ centers within molecular complexes

Developing controlled and reproducible molecular assemblies incorporating lanthanide centers is a crucial step for driving forward up- and down-conversion processes. This challenge calls for the development of strategies to facilitate the efficient in situ segregation of different Ln metal ions into distinct positions within the molecule. The unique family of pure [LnLn'Ln] heterometallic coordination compounds previously developed by us represents an ideal platform for studying the desired Ln-to-Ln' energy transfer (ET). In this context, we report here the new pure one-step synthetically produced [ErNdEr] (3) complex, which allows for the first time at the molecular level to study the mechanisms behind Nd-to-Er energy transfer. To further assess the photophysical properties of this complex, the analogous [LuNdLu] (1) and [ErLaEr] (2) complexes have also been prepared and photophysically studied. Efficient sensitization via the two β-diketones employed as main ligands was probed for both Nd3+ and Er3+ ions, resulting in highly resolved emission spectra and sufficiently long excited state lifetimes, which allowed further assessment of the Ln-to-Ln' ET. This intermetallic transfer was first detected by comparing the emission spectra of iso-absorbant solutions and demonstrated by comparing the lifetime values with or without the lanthanide quencher (Er3+), as well as with a deep analysis of the excitation spectrum of the three complexes. Thus, a very unique phenomenon was discovered, consisting of a mutual Nd-to-Er and Er-to-Nd ET with no net increase of brightness by any metal; while Nd3+ transfers the energy received from the antenna to Er3+, the sensitization of the latter results in back-transfer to Nd3+ into a non-emissive, thus silent, state.

NIR-triggered upconversion and sensitized NIR-emission in Yb-based Eosin Y lake doped latex nanoparticles

Here, Yb-based Eosin Y lakes (EOS-Yb) have been encapsulated in organic nanoparticles (NPs) by microemulsion radical polymerization of methacrylate-based copolymers. These photoactive EOS-Yb NPs emit in the visible and near infrared (NIR) upon excitation at 530 nm and can also display NIR-to-visible upconversion emission upon excitation at 980 nm.

Improved Energy Transfer in the Sensitization of Americium Enables Observation of Circularly Polarized Luminescence

The first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and a chiral diphosphine oxide ligand yielded a complex with strong sensitized metal-centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has often been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of 241Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the 5D1→7F1 transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5 f elements.

Effect of Pyrrolidinedithiocarbamate Ligand on the Luminescence Properties of Heteroligand Samarium and Europium Complexes: Experimental and Theoretical Study

The photophysical properties of two isostructural heteroligand lanthanide complexes of general formula Ln(pdtc)3(phen) (pdtc = pyrrolidinedithiocarbamate anion, phen = 1,10-phenanthroline), Ln = Sm3+ (1), Eu3+ (2)) were studied in solid state and dichloromethane (DCM) solution. The two lanthanide complexes were investigated by experimental techniques for structural (single-crystal X-ray diffraction analysis of 1, powder XRD, TG-DTA) and spectroscopic [electron paramagnetic resonance (EPR), infrared (IR), ultraviolet-visible (UV-vis), photoluminescence (PL)] characterization. DFT/TDDFT/ωB97xD and multireference SA-CASSCF/NEVPT2 calculations with perturbative spin-orbit coupling corrections were applied to construct the Jablonski energy diagrams and to discuss the excited state energy transfer mechanism with competing excited state processes and possible sensitized mechanism of metal-centered emission. The first excited state (S1) involved in the excited state energy transfer L(antenna)-to-Ln was predicted to have interligand (pdtc-to-phen) charge transfer character in contrast to the previously predicted ligand-to-metal charge transfer character. The theoretical consideration showed similar relaxation paths and luminescence quenching channels and appropriate Donor*(phen)-Acceptor*(Ln3+) energy gap for 1 and 2. The experimental measurements in the solid state, however, showed efficient luminescence and good ability to convert UV to visible light only for the Sm(pdtc)3(phen) complex. The minor emission of 2 was explained by partial reduction of Eu3+, confirmed by EPR and calculated electron density distribution data.

Highly Efficient and Thermally Durable Luminescence of 1D Eu3+ Coordination Polymers with Arsenic Bridging Ligands

In this work, bisarsine oxides were evaluated as novel bridging ligands, aiming to develop practical and efficient luminescent lanthanide coordination polymers. We have synthesized one-dimensional (1D) Eu3+ coordination polymers that incorporate bisarsine oxide bridging ligands and hexafluoroacetylacetonate anions. These polymers exhibited a denser packing of chains compared to analogous polymers bridged with bisphosphine oxides. The coordination polymers demonstrated exceptional thermal stability and substantial emission quantum yields. Additionally, the bisarsine oxides induced a pronounced polarization effect, facilitating a sensitive electric dipole transition that yields considerably narrow band red emission. Remarkably, the Eu3+ coordination polymers with bisarsine oxides maintained intense emission even at 550 K. A distinctive feature of these polymers is their heating-induced emission enhancement observed when the temperature was increased from 300 K to 400 K.

Finely manipulating room temperature phosphorescence by dynamic lanthanide coordination toward multi-level information security

Room temperature phosphorescence materials have garnered significant attention due to their unique optical properties and promising applications. However, it remains a great challenge to finely manipulate phosphorescent properties to achieve desirable phosphorescent performance on demand. Here, we show a feasible strategy to finely manipulate organic phosphorescent performance by introducing dynamic lanthanide coordination. The organic phosphors of terpyridine phenylboronic acids possessing excellent coordination ability are covalently embedded into a polyvinyl alcohol matrix, leading to ultralong organic room temperature phosphorescence with a lifetime of up to 0.629 s. Notably, such phosphorescent performance, including intensity and lifetime, can be well controlled by varying the lanthanide dopant. Relying on the excellent modulable performance of these lanthanide-manipulated phosphorescence films, multi-level information encryption including attacker-misleading and spatial-time-resolved applications is successfully demonstrated with greatly improved security level. This work opens an avenue for finely manipulating phosphorescent properties to meet versatile uses in optical applications.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Different anion (NO3- and OAc-)-controlled construction of dysprosium clusters with different shapes

The complex hydrolysis process and strong uncertainty of self-assembly rules have led to the precise synthesis of lanthanide clusters still being in the "blind-box" stage and simplifying the self-assembly process and developing reliable regulation strategies have attracted widespread attention. Herein, different anions are used to induce the construction of a series of dysprosium clusters with different shapes and connections. When the selected anion is NO3-, it blocks the coordination of metal sites around the cluster through the terminal group coordination mode, thereby controlling the growth of the cluster. When NO3- was changed to OAc-, OAc- adopted a bridging mode to induce modular units to build dysprosium clusters through an annular growth mechanism. Specifically, we selected 2-amino-6-methoxybenzoic acid, 2-hydroxybenzaldehyde, and Dy(NO3)3·6H2O to react under solvothermal conditions to obtain a pentanuclear dysprosium cluster (1). The five Dy(III) ions in 1 are distributed in upper and lower planes and are formed by the tight connection of nitrogen and oxygen atoms, and μ3-OH- bridges on the ligand. Next, octa-nuclear dysprosium cluster (2) were obtained by only regulating ligand substituents. The eight Dy(III) ions in 2 are tightly connected through ligand oxygen atoms, μ2-OH-, and μ3-OH- bridges, forming an elliptical {Dy/O} cluster core. Furthermore, only by changing NO3- to OAc-, a wheel-shaped tetradeca-nuclear dysprosium cluster (3) was obtained. Cluster 3 is composed of OAc- bridged multiple template Dy3L3 units and pulling of these template units connected by an annular growth mechanism forms a wheel-shaped cluster. The angle of the coordination site on NO3- is ∠ONO = 115°, which leads to the further extension of the metal sites on the periphery of clusters 1 and 2 through the terminal group coordination mode, thereby regulating the structural connection of the clusters. However, the angle of the coordination site on OAc- is ∠OCO = 128°, and a slightly increased angle leads to the formation of a ring-shaped cluster 3 by connecting the template units through bridging. This is a rare example of the controllable construction of lanthanide clusters with different shapes induced by the regulation of different anions, which provides a new method for the precise construction of lanthanide clusters with special shapes.

Metallo-dithiaporphyrin pigments for bulk-heterojunction solar cell applications: ab initio investigation of structural and optoelectronic properties

Metallo-dithiaporphyrin small molecules have been designed by substituting Ru(ii) with various transition metals at the same oxidation state (M = Mn, Fe, Ni, Cu) as donor materials for Bulk Heterojunction Organic Solar Cells (BHJ-OSCs). Density functional theory (DFT) and time-dependent DFT (TD-DFT) have been used to study the optoelectronic properties of metallo-dithiaporphyrin at various functionals and basis sets. We discovered that the open-circuit voltage (VOC) value increases when Ru(ii) in Ru(S2TTP)Cl2 (S2TTP = tetra-p-tolyldithiaporphyrin) is substituted. In addition, the light harvesting efficiency (LHE) of nickel, manganese, and iron complexes was found to be similar to that of ruthenium, and the iron complex furthermore presented a comparable charge transfer in the excited state corresponding to the Q-band, compared to Ru(S2TTP)Cl2. Hence M(S2TTP)Cl2 (M = Mn, Fe, Ni) appear to be potential low cost candidate donor molecules within a bulk heterojunction solar cell. We further propose suitable engineered acceptor pigments, fitted to provide a good overall solar cell efficiency.

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.

The Effect of Linker-to-Metal Energy Transfer on the Photooxidation Performance of an Isostructural Series of Pyrene-Based Rare-Earth Metal-Organic Frameworks

The tetratopic linker, 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4 TBAPy) along with rare-earth (RE) ions is used for the synthesis of 9 isostructures of a metal-organic framework (MOF) with shp topology, named RE-CU-10 (RE = Y(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III)). The synthesis of each RE-CU-10 analogue requires different reaction conditions to achieve phase pure products. Single crystal X-ray diffraction indicates the presence of a RE9 -cluster in Y- to Tm-CU-10, while a RE11 -cluster is observed for Yb- and Lu-CU-10. The photooxidation performance of RE-CU-10 analogues is evaluated, observing competition between linker-to-metal energy transfer versus the generation of singlet oxygen. The singlet oxygen produced is used to detoxify a mustard gas simulant 2-chloroethylethyl sulfide, with half-lives ranging from 4.0 to 5.8 min, some of the fastest reported to date using UV-irradiation and < 1 mol% catalyst, in methanol under O2 saturation.

Mediating Photochemical Reaction Rates at Lewis Acidic Rare Earths by Selective Energy Loss to 4f-Electron States

Manifesting chemical differences in individual rare earth (RE) element complexes is challenging due to the similar sizes of the tripositive cations and the corelike 4f shell. We disclose a new strategy for differentiating between similarly sized Dy³⁺ and Y³⁺ ions through a tailored photochemical reaction of their isostructural complexes in which the f-electron states of Dy³⁺ act as an energy sink. Complexes RE(hfac)₃(NMMO)₂ (RE = Dy (2-Dy) and Y (2-Y), hfac = hexafluoroacetylacetonate, and NMMO = N-methylmorpholine-N-oxide) showed variable rates of oxygen atom transfer (OAT) to triphenylphosphine under ultraviolet (UV) irradiation, as monitored by ¹H and ¹⁹F NMR spectroscopies. Ultrafast transient absorption spectroscopy (TAS) identified the excited state(s) responsible for the photochemical OAT reaction or lack thereof. Competing sensitization pathways leading to excited-state deactivation in 2-Dy through energy transfer to the 4f electron manifold ultimately slows the OAT reaction at this metal cation. The measured rate differences between the open-shell Dy³⁺ and closed-shell Y³⁺ complexes demonstrate that using established principles of 4f ion sensitization may deliver new, selective modalities for differentiating the RE elements that do not depend on cation size.

Design of Bifunctional Pyclen-Based Lanthanide Luminescent Bioprobes for Targeted Two-Photon Imaging

In the past, Lanthanide Luminescent Bioprobes (LLBs) based on pyclen-bearing π-extended picolinate antennas were synthesized and demonstrated well-adapted optical properties for biphotonic microscopy. The objective of this work is to develop a strategy to design bifunctional analogues of the previously studied LLBs presenting an additional reactive chemical group to allow their coupling to biological vectors to reach deep in vivo targeted two-photon bioimaging. Herein, we elaborated a synthetic scheme allowing the introduction of a primary amine on the para position of the macrocyclic pyridine unit. The photophysical and bioimaging studies demonstrate that the introduction of the reactive function does not alter the luminescent properties of the LLBs paving the way for further applications.

A susceptible coordination hybrid based terbium sensibilization coupled ESIPT effects for pattern discrimination of analogues

Multianalyte detection and analogue discrimination are extremely valuable frontier areas for their wide applications in environmental, medical, clinical and industrial analyses. Nowadays, researchers rack their brains on how to develop excellent multianalyte chemosensors that have presented huge challenges in designing high-efficient fluorescent sensing materials and constructing high-throughput detection methods. In this paper, we propose a novel strategy to utilize the dual-emission fluorescent detection platform as a lab-on-a-molecule, arising from the disalicylaldehyde-coordinated hybrid H₂Q_j3/Tb based terbium sensibilization coupled excited-state intramolecular proton transfer effects. Using the statistical analysis (PCA and HCA) for sensing signals of three fluorescence channels (431, 543 and 583 nm), we demonstrate this elaborate chemosensor with multianalyte detection of three species (solvents, anions and cations) and pattern discrimination of analogues. As a result, the H₂Q_j3/Tb shows great lab-on-a-molecule characters for each set of species, resulting in the easier identification of many critical analytes (e.g., H₂O, NO₂^- and Fe³⁺) and discrimination of analogues. In addition, it is also proven to be able to provide reliable content determination for an analyte, especially the NO₂^- (LOD = 0.37 μM), and discrimination for mixed analogues. A combination of easy-to-implement preparation procedure and data analysis technique makes this work promising for not only designing similar lanthanide-based materials but also realizing more high-efficient multianalyte sensing systems towards various potential applications.

Magnetic and optical studies of a new family of multidimensional and multiproperty PO-lanthanide(III) derived systems

A new family of lanthanide compounds has been synthesized using 1,2-bis(diphenylphosphino)ethane dioxide (dppeO₂) as an O-donor ligand through the phosphoryl group to lanthanide(III) cations and structurally, magnetically and optically studied. Depending on the lanthanide, two different topologies appear: the two-dimensional structure [Ln^III(dppeO₂)_1.5(NO₃)₃(H₂O)_0.5]_n (Ln = Ce (1), Sm (2) and Dy (6)) and the one-dimensional structure [Ln(dppeO₂)(NO₃)₃DMF]_n (Ln = Eu (3), Gd (4) and Tb (5)). Some of the Ln-derived complexes have been used as structural probes, while others have been synthesized to use the specific characteristics of each cation to take advantage of their magnetic/luminescence properties. Complex 6 presents slow relaxation of the magnetization while 2, 3 and 5 present emitting properties in the visible range.

Distributive Nd-to-Yb Energy Transfer within Pure [YbNdYb] Heterometallic Molecules

Facile access to site-selective hetero-lanthanide molecules will open new avenues in the search of novel photophysical phenomena based on Ln-to-Ln' energy transfer (ET). This challenge demands strategies to segregate efficiently different Ln metal ions among different positions in a molecule. We report here the one-step synthesis and structure of a pure [YbNdYb] (1) coordination complex featuring short Yb···Nd distances, ideal to investigate a potential distributive (i.e., from one donor to two acceptors) intramolecular ET from one Nd³⁺ ion to two Yb³⁺ centers within a well-characterized molecule. The difference in ionic radius is the mechanism allowing to allocate selectively both types of metal ion within the molecular structure, exploited with the simultaneous use of two β-diketone-type ligands. To assist the photophysical investigation of this heterometallic species, the analogues [YbLaYb] (2) and [LuNdLu] (3) have also been prepared. Sensitization of Yb³⁺ and Nd³⁺ in the last two complexes, respectively, was observed, with remarkably long decay times, facilitating the determination of the Nd-to-Yb ET within the [YbNdYb] composite. This ET was demonstrated by comparing the emission of iso-absorbant solutions of 1, 2, and 3 and through lifetime determinations in solution and solid state. The comparatively high efficiency of this process corroborates the facilitating effect of having two acceptors for the nonradiative decay of Nd³⁺ created within the [YbNdYb] molecule.

Lanthanide Hexacyanidoruthenate Frameworks for Multicolor to White-Light Emission Realized by the Combination of d-d, d-f, and f-f Electronic Transitions

We report an effective strategy toward tunable room-temperature multicolor to white-light emission realized by mixing three different lanthanide ions (Sm³⁺, Tb³⁺, and Ce³⁺) in three-dimensional (3D) coordination frameworks based on hexacyanidoruthenate(II) metalloligands. Mono-lanthanide compounds, K{Ln^III(H₂O)_n[Ru^II(CN)₆]}·mH₂O (1, Ln = La, n = 3, m = 1.2; 2, Ln = Ce, n = 3, m = 1.3; 3, Ln = Sm, n = 2, m = 2.4; 4, Ln = Tb, n = 2, m = 2.4) are 3D cyanido-bridged networks based on the Ln-NC-Ru linkages, with cavities occupied by K⁺ ions and water molecules. They crystallize differently for larger (1, 2) and smaller (3, 4) lanthanides, in the hexagonal P6₃/m or the orthorhombic Cmcm space groups, respectively. All exhibit luminescence under the UV excitation, including weak blue emission in 1 due to the d-d ³T_1g → ¹A_1g electronic transition of Ru^II, as well as much stronger blue emission in 2 related to the d-f ²D_3/2 → ²F_5/2,7/2 transitions of Ce^III, red emission in 3 due to the f-f ⁴G_5/2 → ⁶H_{5/2,7/2,9/2,11/2} transitions of Sm^III, and green emission in 4 related to the f-f ⁵D₄ → ⁷F_6,5,4,3 transitions of Tb^III. The lanthanide emissions, especially those of Sm^III, take advantage of the Ru^II-to-Ln^III energy transfer. The Ce^III and Tb^III emissions are also supported by the excitation of the d-f electronic states. Exploring emission features of the Ln^III-Ru^II networks, two series of heterobi-lanthanide systems, K{Sm_xCe_1-x(H₂O)_n[Ru(CN)₆]}·mH₂O (x = 0.47, 0.88, 0.88, 0.99, 0.998; 5-9) and K{Tb_xCe_1-x(H₂O)_n[Ru(CN)₆]}·mH₂O (x = 0.56, 0.65, 0.93, 0.99, 0.997; 10-14) were prepared. They exhibit the composition- and excitation-dependent tuning of emission from blue to red and blue to green, respectively. Finally, the heterotri-lanthanide system of the K{Sm_0.4Tb_0.599Ce_0.001(H₂O)₂[Ru(CN)₆]}·2.5H₂O (15) composition shows the rich emission spectrum consisting of the peaks related to Ce^III, Tb^III, and Sm^III centers, which gives the emission color tuning from blue to orange and white-light emission of the CIE 1931 xy parameters of 0.325, 0.333.

Using a dual-emission Sm(iii)-macrocycle as the perceptive lab-on-a-molecule chemosensor toward selective and discriminative detection of nitroaromatic explosives

A dual-emission Sm(iii)-macrocycle Sm-2l is designed as the perceptive lab-on-a-molecule toward selective and discriminative detection of nitroaromatic explosives by statistical analysis.

Modulation of the magnetic and photophysical properties in 3d-4f and 4f-4f' heterobimetallic complexes involving a tetrathiafulvalene-based ligand

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1H-benzimidazol-2-yl)-pyridine ligand (L), 1 equivalent of Ln(hfac)3·2H2O/Dy(tta)3·2H2O (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta- = 2-thenoyltrifluoroacetonate) and M(hfac)2·2H2O leads to the formation of heteroleptic 3d-4f dinuclear complexes of formula [MLn(hfac)5(L)]n (M(II) = Cd, Zn, Co, Mn, Ni and Ln(III) = Dy, Yb, Nd) and [ZnDy(tta)2(hfac)3(L)]·(CH2Cl2). Their X-ray structures reveal that the two coordination sites are occupied by one Ln(III) ion and one M(II) transition metal respectively. The M(II) ions are coordinated to the benzoimidazolylpyridine (bzip) moiety in a N2O4 coordination sphere, while the Ln(III) ions are coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety in a N3O6 surrounding. When Dy(III) ion is used a field-induced Single-Molecule Magnet (SMM) behavior is detected with a magnetic relaxation time slightly dependent to the nature of the vicinal divalent transition metal. On the other hand, when the Yb(III) is used, intense, moderated or quenched 2F5/2 → 2F7/2 NIR luminescence is observed when the Yb(III) ion is respectively associated with the Zn(II), Mn(II) and Ni(II)/Co(II) ion. The emission intensity can be modulated in function of the metal-to-ligand charge transfer and d-d transition intensities. The replacement of the divalent transition metal by a trivalent lanthanide leads to the formation of heteroleptic 4f-4f' dinuclear complexes of formula [Ln2-xLn'x(hfac)6(L)]·a(CH2Cl2)·b(C6H14) and [Dy1.11Nd0.89(tta)3(hfac)3(L)]. The coordination selectivity is based on the radius. Among the 4f-4f' series, the Dy(III) derivatives displayed such ion in N2O6 eight-coordinated sphere allowing the observation of SMM behavior. The three compounds [Dy1.21Nd0.79(hfac)6(L)]·2(CH2Cl2)·(C6H14), [Yb1.04Nd0.96(hfac)6(L)] and [YbPr(hfac)6(L)] displayed respectively Nd(III), modarated Yb(III) and intense Yb(III) NIR emissions.

Dual Emission in the Near-Infrared and Visible Regions from a Mixed Cyanido-Bridged EuIII/NdIII(4-OHpy)-CoIII Layered Material

Coordination polymers (CPs) with a dual emission spanning from the visible (vis) to near-infrared (NIR) regions of the electromagnetic spectrum are used for optical sensors, medical diagnostics, and telecommunication technologies. We herein report the synthesis, structural characterization, and optical response of heterometallic cyanido-bridged layered {[Eu_xNd_y(4-OHpy)₂(H₂O)₃][Co(CN)₆]} CPs, where 4-OHpy = 4-hydroxypyridine, with a multicolor emission profile across the vis and NIR regions. The crystals show an efficient energy transfer (ET) from the 4-OHpy ligand and the [Co(CN)₆] ions to the Eu³⁺ and Nd³⁺ ions, resulting in an enhanced photoluminescence (PL) efficiency. We study the ET with steady-state and time-resolved PL, reporting an ET between the Ln³⁺ centers. The excitation-dependent emission of the mixed Ln³⁺ CPs and the control over the PL lifetime yield new insights into the optoelectronic properties of these materials.

High-efficiency solution-processed OLED based on trivalent europium complex by modifying the composition of the multiple-host system

In this work, di-[4-(N,N-ditolylamino)-phenyl]cyclohexane (TAPC); 4,4′,4″-tri (9-carbazoyl)triphenylamine (TcTa); 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi); and 1,3,5-tri (m-pyrid-3-yl-phenyl)benzene (TmPyPB) were used to constitute the multiple-host system and fabricate solution-processed organic light-emitting diodes (s-OLEDs) with europium complex Eu(DBM)₃Phen (DBM, 1,3-diphenylpropane-1,3-dione; Phen,1,10-phenanthroline) as emitter. In order to determine the optimal composition of the multiple-host system, a series of devices with different light-emitting layers (EMLs) were fabricated and compared. Experimental results revealed that removing TmPyPB out of the multiple-host system greatly reduces the turn-on voltage, whereas the addition of TcTa to the multiple-host system helps facilitate the transfer of holes from TAPC to Eu(DBM)₃Phen molecules, thus increasing the recombination probability of carriers on emitter molecules. Finally, high performance solution-processed red OLED (turn-on voltage of 3.8 V) based on the europium complex doped multiple-host system obtained the maximum current efficiency of 2.07 cd A⁻¹, power efficiency of 1.54 lm W⁻¹, external quantum efficiency of 1.2%, and brightness of 945 cd m⁻².

Carbazole-Functionalized Dipicolinato LnIII Complexes Show Two-Photon Excitation and Viscosity-Sensitive Metal-Centered Emission

Eu^III and Yb^III complexes with the carbazole-dipicolinato ligand dpaCbz^2-, namely K₃[Eu(dpaCbz)₃] and K₃[Yb(dpaCbz)₃], were isolated. The Eu^III complex displayed metal-centred emission upon one-photon excitation with a sensitized emission efficiency Φ L Ln of 1.8±0.3 %, corresponding to an intrinsic emission efficiency Φ Ln Ln of 46% and a sensitization efficiency of η_sens 3.9%, with an emission lifetime of the emissive state τ of 1.087±0.005 ms. The Yb^III complex displayed Φ L Ln of 0.010±0.001 %, and a τ of 2.32±0.06 μs. The Eu^III-centred emission was sensitized as well upon two-photon excitation and a two-photon absorption cross-section σ_2PA of 63 GM at 750 nm was determined for the complex. The one- or two-photon sensitized emission intensity of the Eu^III complex changes by more than two-fold when the solvent viscosity is varied in the range 0.5 - 200 cP and the emission is independent of dissolved oxygen. The Yb^III complex displays a change in emission intensity as well. However, in this case, a dependence of the emission intensity on dissolved oxygen content was observed.

Tuning the photophysical properties of lanthanide(iii)/zinc(ii) 'encapsulated sandwich' metallacrowns emitting in the near-infrared range

A family of Zn16Ln(HA)16 metallacrowns (MCs; Ln = YbIII, ErIII, and NdIII; HA = picoline- (picHA2-), pyrazine- (pyzHA2-), and quinaldine- (quinHA2-) hydroximates) with an 'encapsulated sandwich' structure possesses outstanding luminescence properties in the near-infrared (NIR) and suitability for cell imaging. Here, to decipher which parameters affect their functional and photophysical properties and how the nature of the hydroximate ligands can allow their fine tuning, we have completed this Zn16Ln(HA)16 family by synthesizing MCs with two new ligands, naphthyridine- (napHA2-) and quinoxaline- (quinoHA2-) hydroximates. Zn16Ln(napHA)16 and Zn16Ln(quinoHA)16 exhibit absorption bands extended into the visible range and efficiently sensitize the NIR emissions of YbIII, ErIII, and NdIII upon excitation up to 630 nm. The energies of the lowest singlet (S1), triplet (T1) and intra-ligand charge transfer (ILCT) states have been determined. LnIII-centered total (Q L Ln) and intrinsic (Q Ln Ln) quantum yields, sensitization efficiencies (η sens), observed (τ obs) and radiative (τ rad) luminescence lifetimes have been recorded and analyzed in the solid state and in CH3OH and CD3OD solutions for all Zn16Ln(HA)16. We found that, within the Zn16Ln(HA)16 family, τ rad values are not constant for a particular LnIII. The close in energy positions of T1 and ILCT states in Zn16Ln(picHA)16 and Zn16Ln(quinHA)16 are preferred for the sensitization of LnIII NIR emission and η sens values reach 100% for NdIII. Finally, the highest values of Q L Ln are observed for Zn16Ln(quinHA)16 in the solid state or in CD3OD solutions. With these data at hand, we are now capable of creating MCs with desired properties suitable for NIR optical imaging.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (Ln^III). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Schiff Base Tetranuclear Zn2Ln2 Single-Molecule Magnets bridged by Hydroxamic acid in association with Near-Infrared Luminescence

A series of Zn-Ln heteronuclear SMMs formed by hexadentate compartment Schiff base Zn-precursor and lanthanoid ions were structurally and magnetically characterized, in which the two [Zn-Ln] moieties are bridged by...

Improved emission of Yb(iii) ions in triazacyclononane-based macrocyclic ligands compared to cyclen-based ones

Yb(iii) complexes were synthesised from ligands with a 1,4,7-triazacyclononane (tacn) macrocyclic core. Tacn-based compounds equipped with 2 picolinate arms were more emissive than their tricarboxamide-cyclen analogues carrying the same antenna.

Circularly polarized luminescence of Eu(III) complexes with chiral 1,1'-bi-2-naphtol-derived bisphosphate ligands

The interest for lanthanide circularly polarized luminescence (CPL) has been quickly growing for 10 years. However, very few of these studies have involved correlation between the dissymmetry factor (g_lum ) and the chemical modifications in a series of chiral ligands. Four polymeric compounds of Eu(III) were prepared by using a series of binaphtyl derivatives for which the size of the π system as well as the number of stereogenic elements (i.e., the binaphtyl moiety) are modulated. The resulting {[Eu(hfac)₃ ((S)/(R)-L^x )]}_n (x = 1 and 3) and {[Eu(hfac)₃ ((S,S,S)/(R,R,R)-L^x )]}_n (x = 2 and 4) have been characterized by powder X-ray diffraction by comparison with the X-ray structures on single crystal of the Dy(III) analogs. In solution, the structure of the complexes is deeply modified and becomes monomeric. The nature of the ligand induces change in the shape of the CPL spectra in CH₂ Cl₂ solution. Furthermore, a large |g_lum | = 0.12 of the magnetic-dipole transition for the [Eu(hfac)₃ ((S,S,S)/(R,R,R)-L² )] complex involving the ligand with three stereogenic elements and an extended 𝜋 system has been measured. This report also shows CPL measurements in solid state for the series of {[Eu(hfac)₃ ((S)/(R)-L^x )]}_n (x = 1 and 3) and {[Eu(hfac)₃ ((S,S,S)/(R,R,R)-L^x )]}_n (x = 2 and 4) polymers.

Tuning Excited-State Properties of [2.2]Paracyclophane-Based Antennas to Ensure Efficient Sensitization of Lanthanide Ions or Singlet Oxygen Generation

The multistep synthesis of original antennas incorporating substituted [2.2]paracyclophane (pCp) moieties in the π-conjugated skeleton is described. These antennas, functionalized with an electron donor alkoxy fragment (A¹) or with a fused coumarin derivative (A²), are incorporated in a triazacyclonane macrocyclic ligand L¹ or L², respectively, for the design of Eu(III), Yb(III), and Gd(III) complexes. A combined photophysical/theoretical study reveals that A¹ presents a charge transfer character via through-space paracyclophane conjugation, whereas A² presents only local excited states centered on the coumarin-paracyclophane moiety, strongly favoring triplet state population via intersystem crossing. The resulting complexes EuL¹ and YbL² are fully emissive in red and near-infrared, respectively, whereas the GdL² complex acts as a photosensitizer for the generation of singlet oxygen.

Structural Diversity of Lanthanide 3-Nitrotrispyrazolylborates: Tunable Nuclearity and Intra-Ligand Charge Transfer Sensitization of Visible and NIR Ln3+ Emission

Reported are the syntheses, crystal structures, and photophysical properties of 28, novel lanthanide compounds across five structural types, [Ln(3-NO₂Tp)₂(NO₃)] (1-Ln, Ln = La-Tm, except Pm), [Bu₄N][Ln(3-NO₂Tp)(NO₃)₃] (2-Ln, Ln = Yb, Lu), [Eu(3-NO₂Tp)₂Cl(H₂O)]·2ⁱPrOH (3-Eu), [{Ln(3-NO₂Tp)₂}₂(μ₂-CO₃)]·MeOH (4-Ln, Ln = La-Gd, except Pm), and [{Ln(3-NO₂Tp)}₄(μ₂-OMe)₆(μ₄-O)] (5-Ln, Ln = Pr-Tb, except Pm) with the 3-nitrotrispyrazolylborate (3-NO₂Tp^-) ligand. The reaction of methanol or isopropanol solutions of LnX₃ (X = Cl, NO₃) with the tetrabutyl ammonium salt of the flexidentate 3-NO₂Tp^- ([Bu₄N][3-NO₂Tp]) yields Ln(3-NO₂Tp)_x complexes of various nuclearities as either monomers (1-Ln, 2-Ln, 3-Eu), dimers (4-Ln), or tetramers (5-Ln) owing to the efficient conversion of atmospheric CO₂ to CO₃^2- (dimers) or ligand controlled solvolysis of lanthanide ions (tetramers). 3-NO₂Tp^- is an efficient sensitizer for both the visible and near-IR (NIR) emissions of most of the lanthanide series, except thulium. Optical measurements, supported by density functional theory calculations, indicate that the dual visible and NIR Ln³⁺ emission arises from two intraligand charge transfer (ILCT) transitions of 3-NO₂Tp^-. This is the first report of lanthanide complexes with a nitro-functionalized pyrazolylborate ligand. The derivatization of the known Tp^- ligand results in new coordination chemistry governed by the increased denticity of 3-NO₂Tp^-, imparting remarkable structural diversity and charge transfer properties to resultant lanthanide complexes.

Orbital transitions: insight into energy transfer through an antenna for an organo-lanthanide complex

Supported by experimental work, wavefunction theory (WFT) calculations and density functional theory (DFT) calculations employing a range of functionals have been performed for two lanthanide complexes to investigate, in gas and solution phases, the representations of frontier orbitals and the orbital transitions between singlet states. The orbital transitions calculated using CASSCF/NEVTP2 served as reference. Functionals with a higher proportion of Hartree-Fock exchange gave better agreement with WFT. The choice of functional is therefore important for understanding the nature of orbital transitions and this is especially relevant in formulating antenna-metal ion energy transfer (ET) mechanisms.

Field-Induced SMM and Vis/NIR Luminescence on Mononuclear Lanthanide Complexes with 9-Anthracenecarboxylate and 2,2′:6,2″-Terpyridine

Five new mononuclear lanthanide complexes are synthesized by adding the several lanthanide nitrate hexahydrate salts, which for lanthanide (Ln) are Eu, Tb, Dy, Er, and Yb, with 9-anthracenecarboxylic acid (9-Hanthc) and 2,2′:6,2″-terpyridine (TPY) in mixed solution of methanol and dimethylformamide (DMF). The general formula is [Eu(9-anthc)3(TPY)(DMF)]·H2O (1Eu) where Eu(III) is ennea-coordinated or [Ln(9-anthc)3(TPY)(H2O)]·H2O·DMF (Ln = Tb (2Tb), Dy (3Dy), Er (4Er), and Yb (5Yb)) where Ln(III) is octa-coordinated. For compounds 3Dy, 4Er, and 5Yb, the dynamic ac magnetic study indicated field-induced single molecule magnet (SMM) behavior. The photoluminescence studies in the solid state of these complexes show the sensitization of 4f-4f transitions for 4Er and 5Yb in the NIR region.

Excited State Properties of Lanthanide(III) Complexes with a Nonadentate Bispidine Ligand

EuIII , TbIII , GdIII and YbIII complexes of the nonadentate bispidine derivative L2 (bispidine=3,7-diazabicyclo[3.3.1]nonane) were successfully synthesized and their emission properties studied. The X-ray crystallography reveals full encapsulation by the nonadentate ligand L2 that enforces to all LnIII cations a common highly symmetrical capped square antiprismatic (CSAPR) coordination geometry (pseudo C4v symmetry). The well-resolved identical emission spectra in solid state and in solution confirm equal structures in both media. As therefore expected, this results in long-lived excited states and high emission quantum yields ([EuIII L2 ]+ , H2 O, 298 K, τ=1.51 ms, ϕ=0.35; [TbIII L2 ]+ , H2 O, 298 K, τ=1.95 ms, ϕ=0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.

A Water-Stable Tb-MOF As a Rapid, Accurate, and Highly Sensitive Ratiometric Luminescent Sensor for the Discriminative Sensing of Antibiotics and D2O in H2O

The design and development of self-calibrating ratiometric luminescent sensors for the fast, accurate, and sensitive discrimination and determination of pollutants in wastewater is highly desirable for public and environmental health. Herein, a 3D porous Tb(III)-based metal-organic framework (MOF), {[Tb(HL)(H₂O)₂]·x(solv)}_n (1), was facilely synthesized using a urea-functionalized tetracarboxylate ligand, 5,5'-(((1,4-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))diisophthalic acid (H₄L). The activated framework showed a good water stability in both aqueous solutions at a wide pH range of 2-14 and simulated antibiotic wastewaters. Interestingly, this Tb-MOF exhibited dual luminescence owing to the partial energy transfer from the antenna H₄L to Tb³⁺. More importantly, activated 1 (1a) that was dispersed in water showed a fast, accurate, and highly sensitive discrimination ability toward antibiotics with a good recyclability, discriminating three different classes of antibiotics from each other via the quenching or enhancement of the luminescence and tuning the emission intensity ratio between the H₄L ligand and the Tb³⁺ center for the first time. Simultaneously, 1a is a ratiometric luminescent sensor for the rapid, accurate, and quantitative discrimination of D₂O from H₂O. Furthermore, this complex was successfully used for the effective determination of antibiotics and D₂O in real water samples. This work indicates that 1a represents the first ever MOF material for the discriminative sensing of antibiotics and D₂O in H₂O and promotes the practical application of Ln-MOF-based ratiometric luminescent sensors in monitoring water quality and avoiding any major leak situation.