Europium Β-diketonate Complex Research Articles

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.

Thermally induced structural transitions and temperature memory effect in a luminescent vitrified film of an anisometric europium(III) β-diketonate complex

• Vitrified Eu(DK12-14)3phen film (sandwiched between quartz plates) has been fabricated. • Performed weeklong monitoring revealed temperature memory effect. • Proposed model indicates thermally-induced transitions between two local states of film. • These two states are most likely close to crystalline and amorphous local structures. • Effect could be utilized in designing photonic materials equipped with memory function. We report on a temperature memory effect, which is highly unusual for known film-type materials based on lanthanide(III) β-diketonate complexes. It was observed in a 20 µm thick vitrified film fabricated by cooling the melt of a powder of an anisometric europium(III) β-diketonate complex between two quartz plates. The excitation of the film with light in the wavelength range of 280-425 nm causes a bright orange-red emission of Eu 3+ ions (due to efficient ligand-to-metal energy transfer). The memory effect shows itself as ability of the film to be in different states with their own luminescence decay time at the same temperature. In order to study the effect we carried out a weeklong experiment to monitor the evolution of the luminescence decay time in series of temperature treatments (alternating keeping the film at 370 K and storage in the dark at room temperature). We proposed a simple two-state model to simulate the results of the spectroscopic measurements. This made it possible to reveal the memory effect mechanism, which is thermally induced transitions between two different local states of the film. They are most likely in their nature close to crystalline and amorphous local structures. The obtained and analyzed data clearly indicate that the memory effect observed in the film opens broad perspectives in designing of new type luminescent photonic materials having memory function.

A reusable and self-recoverable vitrified film of an anisometric europium(III) β-diketonate complex with UV light-responsive Eu3+ emission

We report on photophysical properties of a 20 µm thick vitrified film (fabricated from a powder of an anisometric europium(III) β-diketonate complex through a melt-processing technique and sandwiched between two quartz plates), which are highly unusual for known film-type materials based on non-mesogenic lanthanide(III) β-diketonate complexes. The film excited by light in the wavelength range of 280–425 nm exhibits a bright orange-red narrow-band emission of Eu3+ ions (due to efficient ligand-to-metal energy transfer) with 530 µs decay time. The prolonged irradiation of the film with a 337 nm nitrogen laser decreases the luminescence brightness of the Eu3+ ions without decomposition of the anisometric complexes. Then the luminescence gradually recovers during storage of the film in the dark for at least 19 h at room temperature. Interestingly, the film is capable of repeatedly reversible changing the luminescence brightness upon alternating UV laser irradiation and dark storage. The observed self-recovery phenomenon can be presented as an elastic photodeformation of local structures of the film with following changes in the Eu3+ ions emission parameters. We believe that the found film properties are promising for the design and development of novel reusable luminescent sensors or dosimeters of UV radiation.

Thermally Induced Structural Transitions and Temperature Memory Effect in a Luminescent Vitrified Film of an Anisometric Europium(Iii) Β-Diketonate Complex

Thermally Induced Structural Transitions and Temperature Memory Effect in a Luminescent Vitrified Film of an Anisometric Europium(Iii) Β-Diketonate Complex

Dependence of the Operational Characteristics of a Luminescent Temperature Probe Based on a Vitrified Film of a Europium(III) β-Diketonate Complex on the Fixing Technology

Dependence of the Operational Characteristics of a Luminescent Temperature Probe Based on a Vitrified Film of a Europium(III) β-Diketonate Complex on the Fixing Technology

In Situ Interactions of Eu(TTA)3(H2O)2 with Latent Fingermark Components-A Time-Gated Visualization of Latent Fingermarks on Paper.

We introduce a new latent fingermark (LFM) development method, where compounds showing long lifetime luminescence are generated in situ by the reactions of Eu(TTA)3(H2O)2 with LFM components. Until now, time-gated imaging could not be used to develop LFM on porous surfaces due to the difficulties with selective binding of the developing agents to the fingermark ridges. The nature of the interactions of Eu(TTA)3(H2O)2 with the LFM material has been investigated for three model compounds commonly found in the LFM composition-oleic acid, l-serine, and squalene. The LFMs developed with the europium β-diketonate complex have been successfully photographed using a time-gated imaging scheme. The presented new approach has been demonstrated to give similar or better results than developing agents commonly used for paper samples (ninhydrin and 1,2-indanedione). Moreover, contrary to the methods mentioned above, the new approach allows for the development of amino acid-poor LFM on paper.

Elastic changes in luminescence intensity of vitrified film of europium(III) β-diketonate complex

We have observed an elastic change in luminescent properties of a 20 µm thick vitrified film (prepared from an amorphous powder of an anisometric europium(III) β-diketonate complex through a melt-processing technique and sandwiched between two quartz plates) caused by the prolonged UV irradiation. The film under UV light irradiation exhibits a typical Eu3+ ion emission peaked at 611 nm. The irradiation of the film by a 337 nm pulsed nitrogen laser with 0.2 mW average output power for 80 min leads to 1.5-fold decrease in the luminescence intensity at 611 nm. Despite the fact that in the case of traditional film-type materials based on lanthanide(III) β-diketonate complexes such effect is attributed to irreversible ligand photofragmentation, we have observed no photodecomposition of the anisometric complexes in the vitrified film. Moreover, we detected full reversibility of the luminescence intensity by keeping the film in the dark for 21 h. It is worth noting that this feature can be used for the design of new reusable luminescent dosimeters for UV light.

Oxide ancillary ligand-based europium β-diketonate complexes and their enhanced luminosity

Ternary materials of europium complex with 2,2,6,6-tetramethyl-3,5-heptanedione (tmhd) ligand and aqua ligand as ancillary ligands have been prepared and characterized for various optoelectronic characteristics. Reactions of hydrated complex [Eu(tmhd)3(H2O)2] proceeded with triphenylphosphine oxide (TPPO) and pyridine-N-oxide (PNO) ancillary ligands were studied to develop novel complexes. The prepared complexes show good thermal stability. A comparative investigation of prepared materials [Eu(tmhd)3(H2O)2], [Eu(tmhd)3(TPPO)2] and [Eu(tmhd)3(PNO)2] was conducted for their luminescent behaviors in order to obtain the role of ancillary ligand in the enhancement of illumination amount generated from europium (Eu3+) ion. Color coordinates of prepared ternary complexes such as [Eu(tmhd)3(H2O)2] with (x = 0.54, y = 0.32), [Eu(tmhd)3(TPPO)2] with (x = 0.56, y = 0.32) and [Eu(tmhd)3(PNO)2] with (x = 0.57, y = 0.33) indicated that these materials exhibited bright red emission in visible region spectrum. The complexes show a proficient energy transport pathway from the ligands to the innermost Eu3+ by means of an ancillary ligand-sensitized luminescence process. Interaction between the metal and ligand results in a distinguished effect on quantum efficiency (η) as well as on Judd–Ofelt intensity factor (Ω2) of the prepared materials.

Modeling the Kinetics of Luminescence in the 1,4-Dimethylnaphthalene Endoperoxide/Eu(fod)3 System

A study was made of the kinetics of the luminescence of europium(III) β-diketonate complex [Eu(fod)3] in the presence of in situ generated O2(1Δg) at thermal decomposition of the 1,4-dimethylnaphthalene endoperoxide. A scheme was proposed in which the luminescence of Eu(III) (λmax = 615 nm) is determined by the stepwise oxidation of the ligands of the complex, resulting in electronically excited heptafluoro-2-oxo-pentanal and the subsequent transfer of energy to the central cation.

A vitrified film of an anisometric europium(iii) β-diketonate complex with a low melting point as a reusable luminescent temperature probe with excellent sensitivity in the range of 270–370 K

Vitrified film of europium(iii) β-diketonate complex as reusable highly sensitive luminescent temperature probe suitable for long-term monitoring in range of 270–370 K.

Novel trivalent europium β-diketonate complexes with N-(pyridine-2-yl)amides and N-(pyrimidine-2-yl)amides as ancillary ligands: Photophysical properties and theoretical structural modeling

Eighteen new Eu3+ complexes and their Gd3+ analogues with 1,3-diketonate as main ligands and N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands were synthesized. The replacement of water molecules by those amides in the Eu3+ complexes increase the intrinsic quantum yields of luminescence, making them comparable or even more efficient than Eu3+ complexes with standard ancillary ligands such as 2,2′-bipyridine. The luminescence spectra of Gd3+ complexes in comparison with the Eu3+ ones show that efficient ligand-to-metal intramolecular energy transfer processes take place. In most cases the experimental Judd-Ofelt intensity parameters (Ω2 and Ω4) for the Eu3+ complexes show variations as a function of the temperature (77 and 300 K) that overall apparently does not follow clearly any trend. For this reason, geometric variations (on the azimuthal angle φ and ancillary ligands distances) were carried out in the coordination polyhedron for simulating thermally induced structural changes. It has been observed that, in this way, the Ω2 and Ω4 can be satisfactorily reproduced by in silico experiments. It was concluded that, at low-temperature, the ancillary ligands become closer to the Eu3+ ion and the angular variations affect more Ω2 than Ω4, in agreement to the theoretical calculations. The use of N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands in Eu3+ 1,3-diketonates looks to be a good strategy for obtaining highly luminescent complexes.

New insights into UV laser irradiation effect on luminescent behavior of vitrified films based on mesogenic lanthanide(III) β-diketonate complexes

We revealed the effect of the prolonged UV laser irradiation on luminescent behavior of photonic materials based on mesogenic lanthanide(III) β-diketonate complexes by using a novel 3 μm vitrified film of an europium(III) β-diketonate complex. We used the Eu3+ ions to monitor the UV laser-induced photophysical processes in the film. Despite the fact that usually prolonged UV irradiation leads to irreversible photofragmentation of ligands, we had observed no photodecomposition of the complexes after the irradiation of the film with the 337 nm laser for 5 h. The spectroscopic study revealed (i) a 16.5-fold luminescence intensity decrease due to laser-induced changes in inner coordination spheres of the Eu3+ ions and (ii) the main channel of non-radiative energy losses from the Eu3+ ions through the multiphonon relaxation. These features open up new possibilities for designing advanced photonics materials with excellent photostability and luminescent properties controlled during operation.

Luminescent Vesicles and Lyotropic Liquid Crystals in Ethylammonium Nitrate from a Partially Amphiphilic Eu Complex.

Soft luminescent materials have attracted much attention because of their self-assembled and controllable properties. To explore their facile and effective fabrication ways, we report here the self-assembling of luminescent vesicles and lyotropic liquid crystals (LLCs) in a protic ionic liquid, ethylammonium nitrate, by a partially amphiphilic europium β-diketonate complex (Eu(III)) with a 1-dodecyl-3-methylimidazolium cation as the counter ion. An interesting result came from the complex-induced vesicle formation of corresponding amphiphile, 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br), which has been rarely reported in the past. It was the interaction between the Eu(III) and imidazolium group that changed the critical packing parameter of [C12mim]Br, which finally resulted in the occurrence of vesicles. The obtained vesicle aggregates exhibited enhanced fluorescence intensity and lifetime compared to those of Eu(III) solution. Meanwhile, a hexagonal LLC phase with better fluorescence properties was found at higher [C12mim]Br concentration. The obtained photophysical data confirmed that the order degree of Eu(III)-containing aggregates could effectively increase the energy transition efficiency of ligands. The better luminescent properties of LLC resulted from the stronger stabilizing and binding effects on Eu(III) in LLC than that in vesicles, which might be caused by closer molecular packing in LLC. The results presented here will not only expand the strategy of constructing lanthanide-containing luminescent soft materials in ionic liquids but also provide reference to better understand the effect of organized aggregates on luminescence properties.

Temperature-sensitive luminescent photopolymer activated by europium β-diketonate complexes

Photopolymer luminescent compositions containing chelate complexes of Eu3 + with 2-naphthoyltrifluoroacetone and trioctylphosphine oxide as a luminescent dopant have been developed for the photopolymer-based 3-D printing techniques. Photocured samples of photopolymer compositions are transparent in the visible range and have bright red luminescence under the UV excitation. Photophysical studies have revealed that photocured samples possess high quantum yields of luminescence up to 0.59 and monoexponential luminescence decay with 640 μs lifetime at 293 K. It was found that the luminescence of photocured samples is temperature-dependent; the luminescence lifetime of Eu3 + ions decreases threefold during the heating from 293 to 373 K. The combination of monoexponential luminescence decay and high quantum yield is very promising for printing of temperature sensors.

Light-controlled efficient photoluminescence based on an europium β-diketonate complex with single-crystal-to-single-crystal [2+2] cycloaddition.

A brand new europium(iii) β-diketonate complex undergoes a single-crystal-to-single-crystal transformation via [2+2] cycloaddition after UV irradiation, triggering strong Eu(iii) red emission turn-on, which is highly photostable even after 50 hours of irradiation. A photo-patterning process is successfully conducted for security printing application in materials science.

Influence of Europium(III) β-Diketonate Complex on Orientational Responses in Ultrafast Optical Kerr Effect

Experiments on recording the ultrafast optical Kerr effect (OKE) in solution of europium(III) β‑diketonate complexes in toluene at a concentration of 10–2 mol/L showed that the total OKE signal is not a superposition of two contributions, one of which is related to the vibrational–rotational dynamics of toluene molecules, while the other is due to the vibrational–rotational dynamics of the europium(III) complexes. This immediately indicates that the europium(III) complexes essentially change the structure of liquid toluene, which is reflected in the character of an orientational response in picosecond range.

Optical and Chromatic Evaluation of Fluorescent Orthodontic Bonding Materials Doped with a Europium β-diketonate Complex

Optical and Chromatic Evaluation of Fluorescent Orthodontic Bonding Materials Doped with a Europium β-diketonate Complex

Room temperature molecular electrophosphorescence detection in organic LEDs with (Gd, Eu)-β-diketonate complexes blend

In this work is reported the fabrication and characterization of the triple-layer electroluminescent organic devices using a mixture of the gadolinium and europium β-diketonate complexes [GdxEuy(TTA)3 (TPPO)2] as emitting layer. The OLED devices contained the 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1′-diphenylhydrazone (MTCD) as hole-transporting layer and tris(8-hydroxyquinoline aluminum) (Alq3) as electron transporting layer. The electroluminescence spectra present emission narrow bands from 5D1 → 7F1,2 and 5D0 → 7F0,1,2,3,4 transitions characteristics of the Eu3+ ion. These sharp lines are overlapped with a broad band attributed to the electrophosphorescence due to the T1 → S0 transition from TTA ligand. The intermolecular energy transfer from Gd-chelate to Eu-chelate is discussed based on this electrophosphorescence appearance.

Colour tunable emission from Eu0.5Sm0.5(TTA)3 dpphen β-diketonate hybrid organic complex in various organic solvents

We propose the synthesis and charaterization of an orange-red light emitting binuclear Samarium and Europium β-diketonate complex (Sm0.5Eu0.5(TTA)3dpphen) [Sm:Samarium, Eu: Europium, TTA: Thenoyl Trifluoro Acetone, dpphen: bathophenanthroline] by cost effective precipitation technique at pH 7.0, maintaining the stichiometric ratio by mole percentage. The XRD spectrum reveals low crystallinity of the complex and FTIR spectra confirms the structure formation of the complex. Thermogram unveils the thermal stability of the complex as 273.76 °C, while DTA reveals a peak at 507.66 °C, corresponding to the melting point of the complex. UV-Visible absorption spectra of the solvated complex in different basic solvents registers wide band absorption spectra with two sets of peaks, one peaking in the range of 249 - 314 nm and 379-386 nm. PL spectra of the complex in solid state and in solvated state reveal tunable emission from 614 nm to 443 nm when excited at 385 nm. Various photo physical parameters such as absorbance, optical band gap, stokes shift, radiative life time, CIE and CCT were evaluated. These results proved that the synthesized complex have potential as tunable orange-red to blue emissive material for OLED devices, flat panel displays and solid state lighting.

Influence of fluorinated chain length on luminescent properties of [formula omitted][formula omitted]-diketonate complexes

Five novel europium β-diketonate complexes containing a pyrazole fragment were investigated. The influence of the number of fluorine atoms in diketonate ligands on luminescent properties was analyzed. Luminescence intensity of Eu3+ complexes increases significantly when CH bonds with high oscillation energy are replaced with CF bonds with low oscillation energy as the efficiency of energy transfer is improved. Further extension of the fluorinated chain length results in a substantial decrease in non-radiative relaxation rates while the increase in luminescence decay rates is observed. The theoretical results elaborated in terms of Judd-Ofelt theory are in good agreement with the experimental data obtained by time-resolved luminescence spectroscopy.