Influence of Eu(III) Complexes Structural Anisotropy on Luminescence of Doped Conjugated Polymer Blends

Composites Based on Polylactide Doped with Amorphous Europium(III) Complex as Perspective Thermosensitive Luminescent Materials

This work reports fabrication of polylactide (PLA) films doped with various additives of an amorphous Eu(III) complex. We study the temperature behavior of the luminescence intensity and lifetime of the PLA-Eu(III) composites in the range of 298–353 K and investigate the mechanism of luminescence temperature quenching. The peak relative sensitivity of the films reaches 20.1 %×K−1 and exceeds the respective characteristics of all known lanthanide-containing thermosensors designed for the range of physiological temperatures. The produced films can be potential novel materials for luminescent thermosensors.

Temperature-Sensitive Chameleon Luminescent Films Based on PMMA Doped with Europium(III) and Terbium(III) Anisometric Complexes

The spin-coating technique was used to produce composite films consisting of PMMA polymer doped with anisometric complexes of Eu(III) and Tb(III). It was found that an increase in the content of Tb3+ complexes intensifies emission of both ions due to the intermolecular energy transfer from the Tb(III) complex to the Eu(III) complex, which results in the increase in the relative luminescence quantum yield of Eu(III) ion by 36%. The temperature sensitivity of the film luminescence intensity and lifetime in the range of 296–363 K was investigated. The maximum relative sensitivity of the films reaches 5.44% × K−1 and exceeds that of all known lanthanide-containing thermal sensors designed for measuring physiological temperatures. In combination with changing luminescence color, such a sensitivity makes these films promising colorimetric thermal sensors for in situ temperature measurements.

Smart Mn7+ Sensing via Quenching on Dual Fluorescence of Eu3+ Complex-Modified TiO2 Nanoparticles

In this work, titania (TiO₂) nanoparticles modified by Eu(TTA)₃Phen complexes (ETP) were prepared by a simple solvothermal method developing a fluorescence Mn⁷⁺ pollutant sensing system. The characterization results indicate that the ETP cause structural deformation and redshifts of the UV-visible light absorptions of host TiO₂ nanoparticles. The ETP also reduce the crystallinity and crystallite size of TiO₂ nanoparticles. Compared with TiO₂ nanoparticles modified with Eu³⁺ (TiO₂-Eu³⁺), TiO₂ nanoparticles modified with ETP (TiO₂-ETP) exhibit significantly stronger photoluminescence under the excitation of 394 nm. Under UV excitation, TiO₂-ETP nanoparticles showed blue and red emission corresponding to TiO₂ and Eu³⁺. In addition, as the concentration of ETP in TiO₂ nanoparticles increases, the PL intensity at 612 nm also increases. When ETP-modified TiO₂ nanoparticles are added to an aqueous solution containing Mn⁷⁺, the fluorescence intensity of both TiO₂ and ETP decreases. The evolution of the fluorescence intensity ratio (I₁/I₂) of TiO₂ and ETP is linearly related to the concentration of Mn⁷⁺. The sensitivity of fluorescence intensity to Mn⁷⁺ concentration enables the design of dual fluorescence ratio solid particle sensors. The method proposed here is simple, accurate, efficient, and not affected by the environmental conditions.

Eu-phen Bonded Titanium Oxo-Clusters, Precursors for a Facile Preparation of High Luminescent Materials and Films

Incorporation of Eu complexes into various organic or inorganic matrixes is one of the acceptable strategies to obtain displaying materials having practical applications. In this work, we report a convenient approach to preparing high luminescent organic-inorganic hybrid materials and films from the europium-titanium oxo-clusters (EuTOCs) having photoactive antenna ligands. Three Eu₂Ti₄ oxo-clusters were synthesized and crystallographically characterized. They are the first reported lanthanide-TOCs coordinated with 1,10-phenanthroline (phen) and 2,2'-bipyridine (bpy) as photoactive ligands, Eu₂Ti₄O₆(phen)₂(pa)₁₀ (1) (pa = propionate), Eu₂Ti₄O₆(bpy)₂(pa)₁₀ (2), and Eu₂Ti₄O₆(phen)₂(MA)₁₀ (3) (MA = methacrylate). Benefitting from the photoactive antenna ligands and the rigid cluster structures, these clusters showed bright red luminescence with quantum yield in the range of 60-80% and long lifetime up to 3.0 ms. Unlike those physically mixed polymeric materials, the MA coordinated compound 3 can be self-polymerized to form a brilliant luminescent film. The film coated slide was used to develop a fluorescence sensor for biomolecule ascorbic acid (AA). The low detection limit and reusable properties suggest great potential for such EuTOC films in real applications.

Europium-functionalized luminescent titania nanotube arrays: Utilizing interactions with glucose, cholesterol and triglycerides for rapid detection application

In this work, titania nanotube arrays (TiO₂-NTs) were prepared by anodization, and the Eu(III) complexes (Eu (TTA)₃ phen with 2-thenoyltrifluoroacetone (TTA) and 1, 10-phenanthroline (phen)) were successfully coated onto the walls of the nanotubes. When a solution of glucose, cholesterol or triglycerides was dropped onto Eu(III) complex-modified TiO₂-NTs, the fluorescence intensity of this material changes (glucose enhances fluorescence, cholesterol and triglycerides quench fluorescence). These phenomena are explained via an energy transfer process. The sensitivity of the fluorescence intensity to glucose, cholesterol or triglycerides concentration enables design of a multifunctional solid sheet-like detector. Under optimized experimental conditions, the change in fluorescence intensity ratio (ΔF/F₀) is linear with the concentration of glucose, cholesterol or triglycerides. To test the utility of the detector, glucose in orange juice, cholesterol in milk powder, and triglycerides in coconut oil were measured using this method and the results were in good agreement analytical data provided by a food testing company. The new method proposed here is simple, sensitive, reliable and suitable for practical applications.

Preorganized helical chirality controlled homochiral self-assembly and circularly polarized luminescence of a quadruple-stranded Eu2L4 helicate

β-Diketones are one of the most widely used ligands for sensitizing the luminescence of lanthanide complexes due to their excellent sensitization abilities. However, the difficulties in introducing chiral groups to take part in the electronic transitions of conjugated systems limit their application in lanthanide circularly polarized luminescence (CPL) materials. In view of the inherent chirality of the helical structure, herein, a pair of homochiral quadruple-stranded helicates, Eu2L4, is assembled based on chiral bis-β-diketonate ligands, wherein the two point chirality centers in the spacer preorganize the helical conformation of the ligand (3S,4S)/(3R,4R)-3,4-bis(4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenoxyl)-1-benzylpyrrolidine, LSS/LRR. X-ray crystallographic analyses reveal that the R,R configurations of the chiral carbons in the spacer induce the M helical sense of the ligand, while the S,S configurations induce the P helical sense. Through the comprehensive spectral characterization in combination with semiempirical geometry optimization using the Sparkle/RM1 model, it is confirmed that the preorganized ligands successfully control the homochirality of the helicates. Moreover, the mirror-image CD and CPL spectra and NMR measurements confirm the formation of enantiomeric pairs and their diastereopurities in solution. Detailed photophysical and chiroptical characterization studies reveal that the helicates not only exhibit intense circularly polarized luminescence (CPL) with |glum| values reaching 0.10, but also show a high luminescence quantum yield of 34%. This study effectively combines the helical chirality of the helicates with the excellent sensitization ability of the β-diketones, providing an effective strategy for the syntheses of chiral lanthanide CPL materials.

Photostable Anisometric Lanthanide Complexes as Promising Materials for Optical Applications

Uniform luminescent films with high optical quality are promising materials for modern molecular photonics. Such film materials based on β-diketonate complexes of lanthanides have the following application problem: rapid luminescence degradation under UV radiation, low thermostability, poor mechanical properties, and aggregation propensity. An alternative approach to solving these problems is the use of anisometric analogues of β-diketonate compounds of lanthanides (III). The main advantage of such compounds is that they do not crystallize because of long hydrocarbon substituents in the structure of complexes, so they can be used to fabricate thin nano-, micro-, and macroscale uniform film materials by a melt-processing technique at relatively low temperatures, as well as by spin-coating. The method of fabrication of microscale luminescent film materials with controlled optical properties from anisometric analogues of Ln(DBM)3Phen and Ln(bzac)3Phen complexes (Ln = Eu, Tb) is proposed in this paper. Within the framework of this research, we developed original films which are highly uniform and transparent. An important advantage of these films is their high photostability and potential for applications as reusable luminescent sensors and light converters.

Optical and structural characteristics of PMMA films doped with a new anisometric EuIII complex

A new film material capable of transforming UV radiation into visible light was obtained from a highly anisometric Eu^III complex with organic ligands in a polymethylmethacrylate (PMMA) matrix and then structurally characterized. An important advantage of the synthesized complex is its good solubility in organic solvents such as dichloromethane, chloroform, THF, toluene, etc. The ligand environment (flexible alkyl and cyclohexyl substituents) of the Eu^III complex was selected to prevent crystallization, to inhibit the formation of defects in the structure of films and to provide its uniform distribution in the polymer during polymerization. As a result we obtain an Eu^III complex of the film with remarkable thermal behavior: the complex melts to isotropic liquid without decomposition, it supercools at ambient temperature and it forms a stable amorphous material at low (up to -30°C) temperatures. The films were prepared by two methods: bulk polymerization and spin coating. A comparison of the differences of luminescent and optical characteristics of micro- and nanosized PMMA films doped with the anisometric Eu^III complex is given. Based on X-ray powder diffraction and small-angle scattering data, it has been supposed that the association of Eu^III complex molecules occurs in the voids of the PMMA matrix and is accompanied by the formation of a nanocrystalline phase. For films obtained by spin coating, a deeper microphase separation is demonstrated than by bulk polymerization. The dimensional characteristics of the nano-associates were determined and a correlation between the method of preparation and the type of distribution of the Eu^III complex in the PMMA matrix is established.