Luminescent Lanthanide Complexes Research Articles

EXAFS characterisation of metal bonding in highly luminescent, UV stable, water-soluble and biocompatible lanthanide complexes

The combination of X-ray diffraction with EXAFS was employed to assess the coordination environment of lanthanide complexes in solutions. This method is based on the assumption that the local structure of lanthanide complexes in solution combines elements of the crystal structure of the complex in the solid state (single- or polycrystalline) and the elements of the local structure of a lanthanide salt, completely dissociated in the solvent (usually chlorides). The success of this approach is demonstrated with the lanthanide (III) 2,3,4,5,6-pentafluorobenzoate complexes, where the local structure in aqueous and methanol solutions were estimated. Moreover, the dissociation degree of the complexes in aqueous and methanol solutions was evaluated.

Electrochemical Modulation of Emission and Coloration by Using Luminescent Lanthanide(III) Complex and Viologen Derivatives via Intermolecular Energy Transfer

Electrochemical Modulation of Emission and Coloration by Using Luminescent Lanthanide(III) Complex and Viologen Derivatives via Intermolecular Energy Transfer

Ga(3+)/Ln(3+) Metallacrowns: A Promising Family of Highly Luminescent Lanthanide Complexes That Covers Visible and Near-Infrared Domains.

Luminescent lanthanide(III)-based molecular scaffolds hold great promises for materials science and for biological applications. Their fascinating photophysical properties enable spectral discrimination of emission bands that range from the visible to the near-infrared (NIR) regions. In addition, their strong resistance to photobleaching makes them suitable for long duration or repeated biological experiments using a broad range of sources of excitation including intense and focalized systems such as lasers (e.g., confocal microscopy). A main challenge in the creation of luminescent lanthanide(III) complexes lies in the design of a ligand framework that combines two main features: (i) it must include a chromophoric moiety that possesses a large molar absorptivity and is able to sensitize several different lanthanide(III) ions emitting in the visible and/or in the near-infrared, and (ii) it must protect the Ln(3+) cation by minimizing nonradiative deactivation pathways due to the presence of -OH, -NH and -CH vibrations. Herein, a new family of luminescent Ga(3+)/Ln(3+) metallacrown (MC) complexes is reported. The MCs with the general composition [LnGa4(shi)4(C6H5CO2)4(C5H5N) (CH3OH)] (Ln-1, Ln = Sm(3+)-Yb(3+)) were synthesized in a one pot reaction using salicylhydroxamic acid (H3shi) with Ga(3+) and Ln(3+) nitrates as reagents. The molecular structure of [DyGa4(shi)4(C6H5CO2)4(C5H5N) (CH3OH)] was obtained by X-ray analysis of single crystals and shows that the complex is formed as a [12-MCGa(III)shi-4] core with four benzoate molecules bridging the central Dy(3+) ion to the Ga(3+) ring metals. The powder X-ray diffraction analysis demonstrates that all other isolated complexes are isostructural. The extended analysis of the luminescence properties of these complexes, excited by the electronic states of the chromophoric ligands, showed the presence of characteristic, sharp f-f transitions that can be generated not only in the NIR (Sm, Dy, Ho, Er, Yb) but also in the visible (Sm, Eu, Tb, Dy, Tm). All Ln-1 complexes possess very high quantum yield values with respect to other literature compounds, indicating a good sensitization efficiency of the [12-MCGa(III)shi-4] scaffold. Especially, as of today, the Yb-1 complex exhibits the highest NIR quantum yield reported for a lanthanide(III) complex containing C-H bonds with a value of 5.88(2)% in the solid state. This work is a significant step forward toward versatile, easily prepared luminescent lanthanide(III) complexes suitable for a variety of applications including highly in demand biological imaging, especially in the NIR domain.

Thiacalix[4]monocrowns with terpyridine functional groups as new structural units for luminescent polynuclear lanthanide complexes

The synthesis and structure of thiacalix[4]monocrowns in 1,3-alternate configuration substituted by terpyridyl fragments on the lower rim are being discussed. It has been shown that the number of oxyethylene units in oligoethylene glycol chain affects the distribution of the yields of the cross-linking products leading to either thiacalix[4]monocrowns or bisthiacalix[4]arenes. Their complexation ability towards alkali metal and lanthanide ions has been studied using liquid extraction and MALDI TOF MS, in addition to luminescent properties of ligands and their lanthanide complexes. The NMR titration data discovered the participation of both crown ether and terpyridyl fragment in the coordination of lanthanide cations. The fluorescent titration showed the nonlinear emission response to the amount of lanthanide ions.

Antiphotobleaching: A Type of Structurally Rigid Chromophore Ready for Constructing Highly Luminescent and Highly Photostable Europium Complexes

Antiphotobleaching is a critical challenge in the field of luminescent lanthanide complexes (LLCs) as well as in many disciplines concerning organic luminescent processes. In this work, a type of structurally rigid organic ligand, 4‐hydroxy‐1,5‐naphthyridine (ND), is developed, which can not only efficiently sensitize the europium emission but also demonstrate unique photostability. A series of ND derivatives with different substituent groups are synthesized and their singlet and triplet excited state energy levels are systematically investigated. Photophysical characterizations of the corresponding europium complexes reveal that the sensitization efficiencies (ηsens) are close to 100% and the total photoluminescence quantum yields can reach up to 84%. Most importantly, these structurally rigid luminescent europium complexes exhibit outstanding photostability and thermostability. Unlike the widely used β‐diketone complexes that are easily photodegraded, ND‐based chelates show no obvious degradation during the UV aging test (10 W m−2 340 nm Ultraviolet A irradiation) within 200 h. Such superior UV resistance is even better than that of the famous compound tris(8‐hydroxyquinolate)aluminum (Alq3). Possible reasons are discussed and a general rule for designing photostable LLCs is proposed. Such a chromophore is very promising for introducing luminescent materials with good photostability in potential application in many disciplines.

The conjugate base of methyl 3-oxobutanoate as an antenna ligand in visible-emitting photoluminescent lanthanide complexes

Luminescent lanthanide complexes with the conjugate base of methyl-3-oxobutanoate were synthesized, characterized and used for the preparation of doped poly(methylmethacrylate) samples.

Thermosensitive Luminescent Lanthanide Complex with Two Photosensitized Ligands

Thermosensitive Luminescent Lanthanide Complex with Two Photosensitized Ligands

Versatile pyridine-2,6-bis-tetrazolate scaffolds for the formation of highly luminescent lanthanide complexes.

Here we report the straightforward synthesis of the ligands L(tz), L(tzC8), L(tzPEG), L(tzAnis) and L(≡Anis) presenting the same pyridine-bistetrazolate (pytz, L) chelating scaffold but different substituents on the para position of the pyridine ring. Its substitution allows the tuning of the solubility of the LnIII complexes [Ln(Li)3]3(-). These new ligands form homoleptic nona-coordinated LnIII complexes of analogous structure and comparable stability in water and methanol. The derivatization of the para position with triazole and substituted triazole groups does not lead to a significant shift of the absorption window, but a shift of 40 nm is observed in ligand L(≡Anis) due to the presence of the p-ethynyl anisole fragment. The L(tzX) series sensitize well, both the Eu and the Tb ions with quantum yields up to 98% for Tb and 43% for Eu, while the ligand L(≡Anis) sensitizes well Eu (QY of 48%) but cannot sensitize Tb due to the position of its triplet state.

Optical detection of small biomolecule thiamines at a micromolar level by highly luminescent lanthanide complexes with tridentate N-heterocyclic ligands

Based on the luminescence properties of lanthanide complexes, we found that very fast and extremely sensitive optical detection of thiamines can be achieved for the first time.

Near-IR luminescent lanthanide complexes with 1,8-diaminoanthraquinone-based chromophoric ligands.

Three new chromophoric anthraquinone-based multidentate ligands have been synthesised in a step-wise manner from 1,8-dichloroanthraquinone. The ligands each comprise two dipicolyl amine units and react with trivalent lanthanide ions to form monometallic complexes of the form [Ln(L)](OTf)3 as indicated by MS studies and elemental analyses. Supporting DFT studies show that the monometallic species are highly favoured (>1000 kJ mol(-1)) over the formation of a 2 : 2 dimetallic congener. Both ligands and complexes absorb light efficiently (ε ∼ 10(4) M(-1) cm(-1)) in the visible part of the spectrum, with λabsca. 535-550 nm through an intramolecular charge transfer (ICT) transition localised on the substituted anthraquinone unit. In all cases the complexes show a fluorescence band at ca. 675 nm due to the ICT emitting state. The corresponding Nd(iii), Yb(iii) and Er(iii) complexes also reveal sensitised near-IR emission characteristic of each ion following excitation of the ICT visible absorption band at 535 nm.

Luminescent neutral lanthanide complexes of 5-aryl-2,2′-bipyridine-6-carboxylic acids, synthesis and properties

Luminescent lanthanide complexes of 4-aryl-1-(2-pyridyl)-6,7-dihydro-5H-cyclopenta[c]pyridine-3-carboxylic acids and 5-tolyl-2,2′-bipyridine-6-carboxylic acid were prepared. The ligands were synthesized using the “1,2,4-triazine” methodology. In one case, the opportunity of copper complex preparation, followed by exchange of the metal cation from copper to europium to overcome synthetic difficulties, was demonstrated. The ability of tuning the properties of the complexes by means of varying the structure of the ligands was demonstrated. In particular, the introduction of the cyclopentene moiety allowed the preparation of highly soluble complexes in non-polar organic solvents.

Visible light-induced lanthanide polymer nanocomposites based on clays for bioimaging applications

Lanthanide complexes have attracted increased attention in recent years for their unique photophysical properties such as large Stokes shifts, narrow bandwidth, long radiative lifetimes, and high luminescence quantum yield. However, low photochemical stability and poor mechanical properties limit the technological applicability of lanthanide complexes. Two natural clay minerals, fibrillar palygorskite (Pal) and tubular halloysite nanotubes (HNTs), are known for their extreme stabilities and high surface area and show promise as new carriers of luminescent lanthanide complexes for further applications. In this report, clay-based lanthanide polymer nanocomposites clay–polyethyleneimine (PEI)–MPTP–Eu(DBM)3 have been fabricated by attaching a lanthanide complex onto the surface of PEI-modified Pal or HNTs. The formed nanocomposites display visible light-excitable features with a wide excitation wavelength range from UV to visible light, a long luminescence lifetime, and improved photoluminescence stability. Their excellent luminescence, high suspension stability, and low cytotoxicity in cell studies result in the potential applications of the as-prepared nanocomposites for cell imaging in biological systems.

Development of a visible-light-sensitized THA-based lanthanide nanocomposite for cell imaging

As is well-known, hydroxyapatite (HA, Ca10(PO4)6(OH)2) is a typical green natural material. Due to its good biodegradability and nontoxic properties, it is promising to act as a carrier of luminescent lanthanide complexes for the further applications. In this work, we synthesize the well-dispersed HA nanoparticles (NPs) by using SiO2 as templates (THA), which is subsequently grafted by a terpyridine derivative. Then, lanthanide europium complex Eu(DBM)3(H2O)2 (HDBM= dibenzoylmethane) is employed to covalently couple with modified THA NPs via ligand exchange reaction, generating a novel THA-based ternary europium nanocomposite. The formed nanocomposite has well dispersion stability and high biocompatibility. Furthermore, THA-based lanthanide nanocomposite exhibits the visible-light excitable feature with a wide excitation wavelength range from UV to visible light (a maximum at 397nm), long luminescence lifetime (303μs) and improved exposure durability. The excellent fluorescence and low cytotoxicity in cell study of the nanocomposite may result in the potential applications of cell imaging in biological systems.

Expanding the Versatility of Dipicolinate-Based Luminescent Lanthanide Complexes: A Fast Method for Antenna Testing.

A dipicolinate (dpa)-based platform for the rapid testing of potential lanthanide-sensitizing antennae was developed; 4-methyl-7-O-alkylcoumarin-appended dpa could sensitize four lanthanides. The platform could be used to estimate the photophysical properties of a more difficult-to-prepare 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid based structure carrying the same antenna.

Improvement in fingerprint detection using Tb(III)-dipicolinic acid complex doped nanobeads and time resolved imaging

This paper deals with the synthesis and application of lanthanide complex doped nanobeads used as a luminescent fingerprint powder. Due to their special optical properties, namely a long emission lifetime, sharp emission profiles and large Stokes shifts, luminescent lanthanide complexes are useful for discriminating against signals from background emissions. This is a big advantage because latent fingerprints placed on multicoloured fluorescent surfaces are difficult to develop with conventional powders. The complex of 2,6-dipicolinic acid (DPA) and terbium ([Tb(DPA)3]3−) is used for this purpose. Using the Stöber process, this complex is incorporated into a silica matrix forming nanosized beads (230–630nm). It is shown that the [Tb(DPA)3]3− is successfully incorporated into the beads and that these beads exhibit the wanted optical properties of the complex. A phenyl functionalisation is applied to increase the lipophilicity of the beads and finally the beads are used to develop latent fingerprints. A device for time resolved imaging was built to improve the contrast between developed fingerprint and different background signals, whilst still detecting the long lasting luminescence of the complex. The developed fingerprint powder is therefore promising to develop fingerprints on multicoloured fluorescent surfaces.

Enhanced electric dipole transition in lanthanide complex with organometallic ruthenocene units.

Enhanced luminescence of a lanthanide complex with dynamic polarization of the excited state and molecular motion is introduced. The luminescent lanthanide complex is composed of one Eu(hfa)3 (hfa, hexafluoroacetylacetonate) and two phosphine oxide ligands with ruthenocenyl units Rc, [Eu(hfa)3(RcPO)2] (RcPO = diphenylphosphorylruthenocene). The ruthenocenyl units in the phosphine oxide ligands play an important role of switching for dynamic molecular polarization and motion in liquid media. The oxidation states of the ruthenocenyl unit (Rc(1+)/Rc(1+)) are controlled by potentiostatic polarization. Eu(III) complexes attached with bidentate phosphine oxide ligands containing ruthenocenyl units, [Eu(hfa)3(RcBPO)] (RcBPO = 1,1'-bis(diphenylphosphoryl)ruthenocene), and with bidentate phosphine oxide ligands, [Eu(hfa)3(BIPHEPO)] (BIPHEPO =1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide), were also prepared as references. The coordination structures and electrochemical properties were analyzed using single crystal X-ray analysis, cyclic voltammetry, and absorption spectroscopy measurements. The luminescence properties were estimated using an optoelectrochemical cell. Under potentiostatic polarization, a significant enhancement of luminescence was successfully observed for [Eu(hfa)3(RcPO)2], while no spectral change was observed for [Eu(hfa)3(RcBPO)]. In this study, the remarkable enhanced luminescence phenomena of Eu(III) complex based on the dynamic molecular motion under potentiostatic polarization have been performed.

Visible-near-infrared luminescent lanthanide ternary complexes based on beta-diketonate using visible-light excitation.

We used the synthesized dinaphthylmethane (Hdnm) ligand whose absorption extends to the visible-light wavelength, to prepare a family of ternary lanthanide complexes, named as [Ln(dnm)3 phen] (Ln = Sm, Nd, Yb, Er, Tm, Pr). The properties of these complexes were investigated by Fourier transform infrared (FT-IR) spectroscopy, diffuse reflectance (DR) spectroscopy, thermogravimetric analyses, and excitation and emission spectroscopy. Generally, excitation with visible light is much more advantageous than UV excitation. Importantly, upon excitation with visible light (401-460 nm), the complexes show characteristic visible (Sm(3+)) as well as near-infrared (Sm(3+), Nd(3+), Yb(3+), Er(3+), Tm(3+), Pr(3+)) luminescence of the corresponding lanthanide ions, attributed to the energy transfer from the ligands to the lanthanide ions, an antenna effect. Now, using these near-infrared luminescent lanthanide complexes, the luminescent spectral region from 800 to 1650 nm, can be covered completely, which is of particular interest for biomedical imaging applications, laser systems, and optical amplification applications.

Novel luminescent lanthanide complexes assembling alumina/titania/silica hybrids through 2-phenylmalonic acid linkage

In this paper, a series of novel inorganic/organic rare earth (europium, terbium) hybrid materials through 2-phenylmalonic acid linkage were synthesized by the sol–gel process. The micro-structure and the luminescent properties of the complicated hybrids were studied in detail by Fourier transform infrared spectroscopy, wide angle x-ray diffraction, themogravimetric analysis, scanning electron microscope, and fluorescence spectra. The above research results indicate that the hybrids possess high thermal-stability, amorphous structure features and especially favorable luminescent performances such as long luminescent decay lifetime, and high quantum yield.

An integrated closed-tube 2-plex PCR amplification and hybridization assay with switchable lanthanide luminescence based spatial detection.

Switchable lanthanide luminescence is a binary probe technology that inherently enables a high signal modulation in separation-free detection of DNA targets. A luminescent lanthanide complex is formed only when the two probes hybridize adjacently to their target DNA. We have now further adapted this technology for the first time in the integration of a 2-plex polymerase chain reaction (PCR) amplification and hybridization-based solid-phase detection of the amplification products of the Staphylococcus aureus gyrB gene and an internal amplification control (IAC). The assay was performed in a sealed polypropylene PCR chip containing a flat-bottom reaction chamber with two immobilized capture probe spots. The surface of the reaction chamber was functionalized with NHS-PEG-azide and alkyne-modified capture probes for each amplicon, labeled with a light harvesting antenna ligand, and covalently attached as spots to the azide-modified reaction chamber using a copper(i)-catalyzed azide-alkyne cycloaddition. Asymmetric duplex-PCR was then performed with no template, one template or both templates present and with a europium ion carrier chelate labeled probe for each amplicon in the reaction. After amplification europium fluorescence was measured by scanning the reaction chamber as a 10 × 10 raster with 0.6 mm resolution in time-resolved mode. With this assay we were able to co-amplify and detect the amplification products of the gyrB target from 100, 1000 and 10,000 copies of isolated S. aureus DNA together with the amplification products from the initial 5000 copies of the synthetic IAC template in the same sealed reaction chamber. The addition of 10,000 copies of isolated non-target Escherichia coli DNA in the same reaction with 5000 copies of the synthetic IAC template did not interfere with the amplification or detection of the IAC. The dynamic range of the assay for the synthetic S. aureus gyrB target was three orders of magnitude and the limit of detection of 8 pM was obtained. This proof-of-concept study shows that the switchable lanthanide luminescent probes enable separation-free array-based multiplexed detection of the amplification products in a closed-tube PCR which can enable a higher degree of multiplexing than is currently feasible by using different spectrally separated fluorescent probes.

Photocytotoxic luminescent lanthanide complexes of DTPA–bisamide using quinoline as photosensitizer

Luminescent lanthanide(iii) complexes of DTPA–bisamide quinoline as photosensitizer were studied for their structures, luminescent properties, binding with DNA and protein, photo-induced DNA cleavage, photocytotoxicity and cellular uptake studies.