Luminescent Lanthanide Complexes Research Articles

Unusually Large Ligand Field Splitting in Anionic Europium(III) Complexes Induced by a Small Imidazolic Counterion.

Luminescent trivalent lanthanide (Ln3+) complexes are compounds of technological interest due to their unique photophysical properties, particularly anionic tetrakis complexes, given their higher stability and emission quantum yields. However, structural studies on the cation-anion interaction in these complexes and the relation of such to luminescence are still lacking. Herein, the cation-anion interactions in two luminescent anionic tetrakis(2-thenoyltrifluoroacetonato)europate(III) complexes with alkylimidazolium cations, specifically 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium are investigated. The Eu3+ complexes were synthesized and characterized by elemental analysis, mass spectrometry, and single-crystal X-ray crystallography, and their luminescence spectra were recorded at 77 K. Quantum chemical calculations were also performed. X-ray crystallography revealed hydrogen bonds between the enolate ligands and imidazolium ring hydrogens. The 1-butyl-3-methylimidazolium complex had two crystallographic Eu3+ sites, also confirmed by luminescence spectroscopy. The 1-ethyl-3-methylimidazolium complex exhibited an unusual 300 cm-1 splitting in the 5D0 → 7F1 transition, as reproduced by ligand field calculations, suggesting a stronger hydrogen bonding due to the smaller substituent. We hypothesize that this strong bonding likely causes angular distortions, resulting in high ligand field splittings.

Luminescence of Lanthanide Complexes in Mesoporous Silica Matrices: A Textbook Example of Tris‐Dipicolinate Europium Complex Adsorbed in SBA‐15

AbstractThe incorporation of luminescent lanthanide complexes in inorganic matrices opens appealing possibilities in the rational upstream conception of new luminescent materials with easier recyclability. In this regard, the influence of SBA‐15 mesoporous silica, as a host matrix, on the photophysical properties of europium‐trisdipicolinate cesium salt is investigated. The lanthanide complex can be completely and reversibly adsorbed on the silica, using incipient wetness impregnation (IWI) in WATER, without the need of anchoring groups or covalent bonding on the silica surface. This specific procedure allows the homogeneous dispersion of the lanthanide complex into the host silica matrix. Appropriately assessing the photophysical properties of the targeted luminescent material proved remarkably challenging, demanding utmost caution, particularly due to the strong scattering of the mesoporous matrices. Additionally, while the observations confirm an important increase of luminescence lifetimes of lanthanide complexes upon integration into these mediums, this variation is attributed to the differing refractive indexes and not to specific surface interactions or confinement effect. Indeed, it appeared that previous literature precedents depicted erroneous exhalations of the complexes intrinsic quantum yield due to the repeated use of erroneous refractive index values. In the meantime, the luminance of these materials under UV irradiation improves drastically in comparison to what is obtained with the physical dispersion of micro‐crystals of the lanthanide complex onto silica. It is demonstrated that this improvement is due to a reduced inner filter effect in the adsorbed samples. In this regard, IWI of lanthanide complexes in the mesoporous matrices method could be of interest in the development of recyclable emitting layers, less demanding in terms of emitter quantity.

Comprehensive Photophysical and Nonlinear Spectroscopic Study of Thioanisolyl‐Picolinate Triazacyclononane Lanthanide Complexes

AbstractDetailed photophysical studies of luminescent lanthanide complexes are presented and elaborated using a newly developed thioanisolyl‐picolinate antenna and the related tacn macrocyclic ligand. The new ligand proved to sensitise Nd(III), Sm(III), Eu(III) and Yb(III) emission. Eu(III) complex showed complete energy transfer, yielding high quantum yield (44 %) and brightness, while the Tb(III) analogue underwent a thermally activated back‐energy transfer, resulting in a strong oxygen quenching of the triplet excited state. Transient absorption spectroscopy measurements of Gd(III), Tb(III) and Eu(III) compounds confirmed the sensitization processes upon the charge‐transfer antenna excitation. The triplet excited state lifetime of the Tb(III) complex was 5‐times longer than that of the Gd(III) analogue. In contrast, the triplet state was totally quenched by the energy transfer to the 4f‐metal ion in the Eu(III) species. Nonlinear two‐photon absorption highlighted efficient biphotonic sensitization in Eu(III) and Sm(III) complexes. In case of the Nd(III) compound, one‐photon absorption in 4f–4f transitions was predominant, despite the excitation at the antenna two‐photon band. This phenomenon was due to the Nd(III) 4f–4f transitions overlapping with the wavelength‐doubled absorption of the complex.

Luminescent lanthanide complexes based on 4,5-di(3,5-dicarboxylphenoxy)phthalic acid as enhanced fluorescence probes for highly selective detection of lead(II) ions in water.

Six novel lanthanide complexes ([Nd2(L)(H2O)6]n·4.58n(H2O) (1), [Ln(H3L)(H2O)]n·0.5n(H2O), Ln = Sm (2), Eu (3), Gd (4), Tb (5), Eu0.18Gd0.62Tb0.20 (6)) have been hydrothermally synthesized based on the ligand 4,5-di(3,5-dicarboxylphenoxy)phthalic acid (H6L). Single crystal X-ray diffraction reveals that complexes 1-6 are 2D structures, where 2-6 are isomorphic. Complexes 3 and 5 exhibit the characteristic fluorescence of Eu(III) and Tb(III) ions respectively, while complex 4 shows blue-green light emission based on the ligand. In particular, the ternary Eu/Gd/Tb complex 6 shows white light emission with a CIE (Commission International del'Eclairage) chromaticity coordinate of (0.330, 0.339) and hence close to pure white light emission. Moreover, complexes 3 and 5 display specific fluorescence-enhanced detection performance for Pb2+ ions: The interaction between Pb2+ ions and the ligand enhances the charge transfer efficiency between the ligand and the Eu(III) and Tb(III) ions and thus leads to fluorescence enhancement of complexes 3 and 5. More importantly, complex 3 exhibits the lowest detection limit of 4.72 nM for Pb2+ ions among the existing complex fluorescent probes. In addition, both complexes 3 and 5 show good performance for recycling and for the detection of Pb2+ in real water samples.

A bimodal time-gated luminescence-magnetic resonance imaging nanoprobe based on a europium(III) complex anchored on BSA-coated MnO2 nanosheets for highly selective detection of H2O2.

A novel nanocomposite, [Eu(BTD)3(DPBT)]-BSA@MnO2, is reported to serve as an effective nanoprobe for bimodal time-gated luminescence (TGL) and magnetic resonance (MR) imaging of H2O2in vitro and in vivo. The nanoprobe was fabricated by immobilizing visible-light-excitable Eu3+ complexes in bovine serum albumin (BSA)-coated lamellar MnO2 nanosheets. The TGL of the Eu3+ complex was effectively quenched by the MnO2 nanosheets. Upon exposure to H2O2, the MnO2 nanosheets underwent reduction to Mn2+, which simultaneously triggered rapid, selective and sensitive "turn-on" responses toward H2O2 in both TGL and MR detection modes. The presence of a protective "corona" formed by BSA enables the nanoprobe to withstand high concentrations of glutathione (GSH), a strong reducing agent of MnO2 nanosheets. This capability allows the nanoprobe to be utilized for detecting H2O2 in living biosamples. The combined utilization of TGL and MR detection modes enables the nanoprobe to image H2O2 across a wide range of resolutions, from the subcellular level to the whole body, without any depth limitations. The results obtained from these modes can be cross-validated, enhancing the accuracy of the detection. The capability of the nanoprobe was validated by TGL imaging of endogenous and exogenous H2O2 in live HeLa cells, as well as bimodal TGL-MR imaging of H2O2 in tumor-bearing mice. The research achievements suggest that the integration of luminescent lanthanide complexes with protein-coated MnO2 nanosheets offers a promising bimodal TGL-MR sensing platform for H2O2in vitro and in vivo.

Photoswitchable luminescent lanthanide complexes controlled and interrogated by four orthogonal wavelengths of light.

Optical information storage requires careful control of excitation and emission wavelengths in a reversible and orthogonal manner to enable efficient reading, writing, and erasing of information. Photochromic systems, in which a photoswitch is typcially coupled to an emissive organic fluorophore, have much promise in this regard. However, these suffer from considerable spectral overlap between the switch and fluorophore, such that their emissive and photoswitchable properties are not orthogonal. Here, we overcome this limitation by coupling visible/NIR emissive lanthanide complexes with molecular photoswitches, enabling reversible and orthogonal photoswitching with visible light. Crucially, photoswitching does not lead to sensitised emission from the lanthanide, while excitation of the lanthanide does not induce photoswitching, enabling the state of the system to be probed without perturbation of the switch. This opens up the possibility of developing multi-colour read-write methods for information storage using emissive photoswitches.

Targeted, Molecular Europium(III) Probes Enable Luminescence-Guided Surgery and 1 Photon Post-Surgical Luminescence Microscopy of Solid Tumors.

Discrete luminescent lanthanide complexes represent a potential alternative to organic chromophores due to their tunability of optical properties, insensitivity to photobleaching, and large pseudo-Stokes shifts. Previously, we demonstrated that the lack of depth penetration of UV excitation required to sensitize discrete terbium and europium complexes can be overcome using Cherenkov radiation emitted by clinically employed radioisotopes in situ. Here, we show that the second-generation europium complexes [Eu(III)(pcta-PEPA2)] and [Eu(III)(tacn-pic-PEPA2)] (Φ = 57% and 76%, respectively) lower the limit of detection (LoD) to 1 nmol in the presence of 10 μCi of Cherenkov emitting isotopes, 18F and 68Ga. Bifunctionalization provides access to cysteine-linked peptide conjugates with comparable brightness and LoD. The conjugate, [Eu(tacn-(pic-PSMA)-PEPA2)], displays high binding affinity to prostate-specific membrane antigen (PSMA)-expressing PC-3 prostate cancer cells in vitro and can be visualized in the membrane-bound state using confocal microscopy. Biodistribution studies with the [86Y][Y(III)(tacn-(pic-PSMA)-PEPA2)] analogue in a mouse xenograft model were employed to study pharmacokinetics. Systemic administration of the targeted Cherenkov emitter, [68Ga][Ga(III)(PSMA-617)], followed by intratumoral injection or topical application of 20 or 10 nmol [Eu(III)(tacn-(pic-PSMA)-PEPA2)], respectively, in live mice resulted in statistically significant signal enhancement using conventional small animal imaging (620 nm bandpass filter). Optical imaging informed successful tumor resection. Ex vivo imaging of the fixed tumor tissue with 1 and 2 photon excitation further reveals the accumulation of the administered Eu(III) complex in target tissues. This work represents a significant step toward the application of luminescent lanthanide complexes for optical imaging in a clinical setting.

Quantitative and Multiplexed Chopper-Based Time-Gated Imaging for Bioanalysis on a Smartphone.

Smartphones are emerging platforms for point-of-care diagnostics (POCDs), where the on-board camera is, for example, used to image fluorescence. Many laboratory instruments are capable of time-gated (TG) photoluminescence (PL) measurements─an analytical method leveraged by multiple commercial assay kits. When paired with long-lived PL emitters such as luminescent lanthanide complexes (LLCs), time-gating eliminates background from sample autofluorescence and many other sources. This capability is amenable to minimally processed samples and would thus be useful for POCDs on a smartphone-based platform. Here, we report a double-chopper design for TG PL imaging using a portable, 3D-printed, smartphone-based device. The rotation speed, dimensions, and overlap of the chopper blades and gaps set the timing parameters, with delay times on the order of hundreds of microseconds to milliseconds. The device was capable of quantitative TG imaging of PL from terbium(III) and europium(III) LLCs, including rejection of short-lived PL background from serum and tissue phantoms, spectral and temporal multiplexing, a model time-gated Förster resonance energy transfer (TG-FRET) assay, and imaging of cells. As the first smartphone-based demonstrations of these important analytical capabilities, this work is an important foundation for developing POCD methods based on TG PL imaging.

Thermally-assisted photosensitized emission in a trivalent terbium complex

Luminescent lanthanide complexes containing effective photosensitizers are promising materials for use in displays and sensors. The photosensitizer design strategy has been studied for developing the lanthanide-based luminophores. Herein, we demonstrate a photosensitizer design using dinuclear luminescent lanthanide complex, which exhibits thermally-assisted photosensitized emission. The lanthanide complex comprised Tb(III) ions, six tetramethylheptanedionates, and phosphine oxide bridge containing a phenanthrene frameworks. The phenanthrene ligand and Tb(III) ions are the energy donor (photosensitizer) and acceptor (emission center) parts, respectively. The energy-donating level of the ligand (lowest excited triplet (T1) level = 19,850 cm−1) is lower than the emitting level of the Tb(III) ion (5D4 level = 20,500 cm−1). The long-lived T1 state of the energy-donating ligands promoted an efficient thermally-assisted photosensitized emission of the Tb(III) acceptor (5D4 level), resulting in a pure-green colored emission with a high photosensitized emission quantum yield (73%).

Synthesis, Spectral Characterization and Potential Fluorescent Properties of Three Lanthanide(III) Ions Complexes with Nalidixic Acid.

Three new solid lanthanide complexes with nalidixic acid (HNal) with the stoichiometry [Ln(Nal)3]·5·.5H2O (Ln=Tb, Dy and Ho) were synthesized applying the green synthesis method from the aqueous solutions without the organic solvent addition and fully characterized by the elemental analysis, XRF, complexometric titration, gravimetric analysis, molar conductivity and solubility measurements, powder X-Ray diffraction, UV-Vis and infrared (FT-IR) spectroscopies. Moreover, the luminescent properties of the Tb(III), Dy(III), and Ho(III) complexes in the solid state and in the solutions were investigated. On the basis of the detailed spectral analysis, it was concluded that the nalidixate ligands bind to the lanthanide ions by the bidentate carboxylate and carbonyl groups while water molecules belong to the outer coordination sphere. At the excitation of UV light, the complexes exhibited characteristic emission of central lanthanide ions, the intensity of which depends significantly on the excitation wavelength and/or the solvent. Thus, the application of nalidixic acid (apart from biological activity) for the synthesis of luminescent lanthanide complexes was confirmed which can find potential applications in the field of photonic devices and/or bioimaging agents.

Rapid handheld time-resolved circularly polarised luminescence photography camera for life and material sciences

Circularly polarised luminescence (CPL) is gaining a rapidly increasing following and finding new applications in both life and material sciences. Spurred by recent instrumental advancements, the development of CPL active chiral emitters is going through a renaissance, especially the design and synthesis of CPL active luminescent lanthanide complexes owing to their unique and robust photophysical properties. They possess superior circularly polarised brightness (CPB) and can encode vital chiral molecular fingerprints in their long-lived emission spectrum. However, their application as embedded CPL emitters in intelligent security inks has not yet been fully exploited. This major bottleneck is purely hardware related: there is currently no suitable compact CPL instrumentation available, and handheld CPL photography remains an uncharted territory. Here we present a solution: an all solid-state small footprint CPL camera with no moving parts to facilitate ad hoc time-resolved enantioselective differential chiral contrast (EDCC) based one-shot CPL photography (CPLP).

Impact of chiral ligands on photophysical and electro-optical properties of β-diketonate europium complexes in circularly polarized OLEDs.

Luminescent lanthanide complexes exhibiting chiroptical properties are attracting attention for their application in chiral optoelectronics and photonics, thanks to their unique optical properties, allied to intraconfigurational f-f transitions, which are generally electric-dipole-forbidden and can be magnetic dipole-allowed, which in an appropriate environment can lead to high dissymmetry factors and strong luminescence, in the presence of an antenna ligand. However, because luminescence and chiroptical activity are governed by different selection rules, their successful application in commonly used technologies is still an expectation. Recently, we showed that europium complexes bearing β-diketonates acting as luminescence sensitizers, and chiral bis(oxazolinyl) pyridine derivatives as the chirality inducer, reasonably perform in circularly polarized (CP) organic light-emitting devices (OLEDs). Indeed, europium β-diketonate complexes are an interesting molecular starting point, given their strong luminescence and their established use in conventional (i.e., nonpolarized) OLEDs. In this context, it is interesting to investigate in detail the impact of the ancillary chiral ligand on complex emission properties and the performances of corresponding CP-OLEDs. Here we show that, by incorporating the chiral compound as emitter in the architecture of solution processed electroluminescent devices, CP emission is retained, and the efficiency of the device is comparable to reference unpolarized OLED. The observed remarkable dissymmetry values strengthen the position of chiral lanthanide-OLEDs as CP-emitting devices.

Fabrication of Eu3+-dipicolinic acid complex functionalized nanoSiO2 composites and their Langmuir-Blodgett films as visual fluorescence probe for tetracycline and oxytetracycline

Luminescent lanthanide complexes have attracted growing attention in the visual probe for detection of toxic and dangerous materials. Here, we report an interfacial self-assembly of Eu3+-dipicolinic acid complex functionalized nanoSiO2 composites (nanoSiO2PyTAEu) and their Langmuir-Blodgett (LB) films as well as the luminescent probes to tetracycline (TC) and oxytetracycline (OTC). Organic linkers and Eu3+ ions are anchored on the hydrophilic nanoSiO2 particles’ surface via the surface silanization, substitution and coordination reactions, so they exhibit high stability and well distribution in the solutions and LB films. Both the nanocomposites of nanoSiO2PyTAEu and their LB films show strong and enhanced red fluorescence emissions of Eu3+ ions when they are immersed in the aqueous TC solution, with the detection limit to 3.3 and 0.91 nmol/L, respectively. The present nanocomposites and LB films have the advantages of high sensitivity and stability.

Shape memory luminescent cellulose/chitosan hydrogel for high sensitive detection of formaldehyde

Hybrid hydrogels containing biomacromolecules have been widely used in sensors, fluorescent probes, and other fields due to their high biocompatibility and nontoxicity. In this paper, tough hydrogels with interconnected macro-pores have been fabricated by freeze-induced chemical cross-linking of microfibrillated cellulose (MFC) and organic modified chitosan (CS). In this hydrogel materials, three-dimensional networks were formed by abundant hydrogen bonds and chemical cross-linking. Luminescent lanthanide complexes were covalently bonded to the hydrogel networks through coordination of Eu3+ ions with 2, 3-pyridine dicarboxylic acid modified chitosan. The luminescence of hydrogel materials was further improved by the replacement of coordination water with 2-thiophenyltrifluoroacetone (TTA). The prepared hydrogels showed excellent shape memory properties both under water and in air. The stress of the hybrid hydrogel at 80 % strain can reach 159 kPa, which is much higher than that of the traditional microfibrillated cellulose-based hydrogels. The obtained luminescent hybrid hydrogels exhibited an excellent fluorescence detection effect on formaldehyde. The detection limit for formaldehyde is 45.7 ppb, which is much lower than the WHO standard (80 ppb for indoor air). The novel, facile preparing procedure may extend the potential applications of hybrid lanthanide luminescent hydrogel as fluorescence probes for pollution monitoring, especially for formaldehyde and other organic aldehydes.

Stable chitosan fluorescent nanofiber sensor containing Eu3+ complexes for detection of copper ion

In this work, a luminescent lanthanide complex, namely, Eu(tta)3phen (Eu = europium, tta = 2-thenoyltrifluoroacetone, phen = 1, 10-phenanthroline) is used as a luminescent dopant to prepare fluorescent nanofiber films. The resulting nanofibers (CS/PEO-SiO2@Eu(tta)3phen) are composed of chitosan and polyethylene oxide containing silica nanoparticles, encapsulating the Eu(tta)3phen. The nanofibers are stabilized by treatment with sodium bicarbonate (NaHCO3) aqueous solution as neutralizer and then repeatedly washed with deionized water. A more stable Na-CS/PEO-SiO2@Eu(tta)3phen fiber film is obtained as a fluorescence sensor for Cu2+ ions. The Na-CS/PEO-SiO2@Eu(tta)3phen has high sensitivity, and a wide detection range. The response is linear in the concentration range from 10 to 90 μmol/L, and the detection limit is 0.826 μmol/L. In addition, Na-CS/PEO-SiO2@Eu(tta)3phen nanofiber film can be used as a recyclable sensor for the detection of Cu2+ ions in aqueous solution due to its good recyclability, selectivity and rapid optical response.

Multi-stimuli responsive lanthanides-based luminescent hydrogels for advanced information encryption

The development of information storage materials and techniques with enhanced security level is still great challenging. Herein, the luminescent hydrogels were facilely prepared by doping luminescent lanthanide complexes into non-covalent cross-linked gelatin/poly(vinyl alcohol) hydrogels. The acquired luminescent hydrogels exhibited reversible luminescent switching behavior upon HCl/NH3 and Fe3+/EDTA2− stimuli, respectively. Remarkably, such reversible luminescent switching property of the hydrogels allows themselves as good candidates for rewritable information security storage. The written patterns were invisible under daylight, however can be clearly observed under UV light, suggesting their potential applications in information protection. Moreover, luminescent hydrogels with low toxicity possessed appealing shape memory and self-healing properties simultaneously. The combination of shape memory and self-healing properties with reversible luminescent switching property can access advanced information encryption effectively. Such encrypted information can only be decrypted by specific predesigned procedures with multi-steps. This work provides an alternative strategy to design and fabricate smart optical soft materials for advanced information encryption.

Eu3+/Tb3+ bimetallic complex-doped siloxane-polyether hybrid film for luminescent thermometry

Developing a contactless ratiometric luminescent thermometry with high sensitivity, widely available temperature range, and reliable performance is still a challenge in materials science. Herein, we adopted an in-situ formation strategy to synthesize luminescent lanthanide complexes in siloxane-polyether matrix by the reaction between 4′-(4-carboxyphenyl)- 2,2′:6′,2″- terpyridine (Hcptpy) ligand and lanthanide ions (Eu3+/Tb3+) to realize a ratiometric luminescent thermometer. The unique energy cascade from Hcptpy → Tb3+ → Eu3+ in siloxane-polyether enables the luminescent films to be not only the multi-color emission, but also provide highly temperature-sensitive over the wide temperature range. The EuTb15@SP film for luminescent thermometry performance is fine-tuned to reach a maximum relative sensitivity of 7.26% K−1 at 397 K and shows repeated utilization without sensitivity loss. Furthermore, the multi-color emission ranging from red through yellow to green can be achieved by tuning the Eu3+/Tb3+ molar ratio. Consequently, utilizing siloxane-polyether as matrix has been proven to be an effective strategy for constructing lanthanide-based hybrid films with temperature sensor properties. We believe that the reported strategies for preparing a bimetallic complex-doped siloxane-polyether hybrid film will broaden potential applications.

Nanoarchitectonics of Ln3+ (Eu3+/Tb3+)-induced polyelectrolyte aggregates (LIPAs) for multicolor luminescence in 3D-printed poly(Lactic acid)

Reversible bright-dark luminescence nanomaterials have been developed for information storage and anti-counterfeiting in recent years, however, their monochrome characteristic and 2D patterning impose limits on the effective information storage density. In this work, a new strategy for producing ultraviolet switchable and stable luminescent patterns is proposed, based on Ln3+ (Eu3+/Tb3+) induced-polyelectrolyte aggregates (LIPAs) with sharp multi-color optical properties. Under 365 nm excitation, a multicolor pattern can be observed using both red and green, which is not visible when this excitation light source is off. The LIPAs enable the luminescent lanthanide complexes to be compatibilized with poly(lactic acid) (PLA). Functional anti-counterfeiting patterns were prepared by 3D printing using luminescent PLA containing by Ln3+ (Eu3+/Tb3+) LIPAs. Invisible, adjustable and ultra-stable multicolor luminescent patterns well enable information storage and enhance information security for anti-counterfeiting applications.

Effect of disubstitution pattern of the terminal alkyl chains on the mesophase of liquid crystals based on lanthanide(III) complexes: A study of the thermal, emission and dielectric behavior

In the present work, new luminescent lanthanide complexes with extended mesomorphic range were prepared by coordination to lanthanide ions (Eu3+, Sm3+ and Tb3+) of the new 4-pyridone based organic ligands (L) with 3,4- (7-n) and 3,5-di(alkyloxy)benzyl (8-n) mesogenic groups and variable length (n = 12 or 14 carbon atoms) onto the benzyl unit. The cumulative results of the elemental analyses as well as the 1H, 13C NMR and IR spectroscopies support the structure of the organic derivatives and their lanthanide complexes [LnL3(NO3)3] (9-n/Ln and 10-n/Ln) described in this work. These complexes show characteristic lanthanide solid state emission, both at room and elevated temperatures corresponding to crystalline, glassy or liquid crystal states. The long range SmA phases displayed by all complexes were supported by a combination of characterization methods, including: differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature powder X-ray diffraction (XRD). This work shows that the number, substitution pattern and length of flexible alkoxy chains are important parameters to control the phase-transition characteristics of the lanthanide complexes. Complexes with 3,4-disubstituted pattern (9-n/Ln) show higher clearing temperatures (nearly 60 °C for Eu3+, 70 °C for Sm3+ and 85 °C for Tb3+ complexes) compared to their counterparts with 3,5-disubstituted pattern (10-n/Ln). Moreover, complexes 9-n/Ln crystallize when cooling their LC phase while complexes 10-n/Ln are stable in glassy state at room temperature as a consequence of the different close interdigitated molecular packing evidenced by XRD measurements. Dielectric spectroscopy was employed to detect the changes of order degree specific to each phases (crystalline, LC or isotropic). The variation of dielectric constant and the electrical conductivity versus temperature shows three transition intervals for selected complexes 10-14/Sm and 10-14/Tb, which delimit the main intervals: 45–60 °C, 90–110 °C; 140–160 °C corresponding to the Cr1-Cr2, Cr2 – SmA and SmA-Iso transitions, and agree very well with the DSC results. The change of characteristic time, obtained by Havriliak-Negami fit function, with temperature also provides a very good correlation with the DSC and POM results.

Metal Ion-Directed Specific DNA Structures and Their Functions.

Various DNA structures, including specific metal ion complexes, have been designed based on the knowledge of canonical base pairing as well as general coordination chemistry. The role of metal ions in these studies is quite broad and diverse. Metal ions can be targets themselves in analytical applications, essential building blocks of certain DNA structures that one wishes to construct, or they can be responsible for signal generation, such as luminescence or redox. Using DNA conjugates with metal chelators, one can more freely design DNA complexes with diverse structures and functions by following the simple HSAB rule. In this short review, the authors summarize a part of their DNA chemistries involving specific metal ion coordination. It consists of three topics: (1) significant stabilization of DNA triple helix by silver ion; (2) metal ion-directed dynamic sequence edition through global conformational change by intramolecular complexation; and (3) reconstruction of luminescent lanthanide complexes on DNA and their analytical applications.