Light Conversion Molecular Devices Research Articles

Syntheses and characterization of Schiff base ligands and their Ir(III) complexes as coating for phosphor-converted LEDs

Ir(III) complexes find several applications in light conversion molecular devices (LCMD) such as in solid-state lighting (SSL). Although, a couple of blue or green-emitting Ir(III) complexes are found so far, there is a lack of near-UV-to-red downshifting converter Ir(III) complexes to be used as coatings of near-UV-excited white-light-emitting diodes (WLEDs). Thus, in this study, we introduce the syntheses of two ligands named as 2-(((3-methyl-1-phenyl-1H-pyrazol-5-yl)imino)methyl)phenol (BS1) and 5-(diethylamino)-2-(((3-methyl-1-phenyl-1H-pyrazol-5-yl)imino)methyl)phenol (BS2) and their use to synthesize two new red-emitting iridium complexes, Ag[Ir(ppz)2(BS1)] and Ag[Ir(ppz)2(BS2)]. BS1 and BS2 structures were deeply investigated theoretically and experimentally, and they display emission in the yellow and green spectral region under UV excitation, respectively. Ag[Ir(ppz)2(BS1)] and Ag[Ir(ppz)2(BS2)] features emission characterized by a broadband centered with color coordinates of (0.659;0.337) and (0.612;0.380), respectively, both in the red spectral region, with 100 % of color purity. To demonstrate their application in SSL, BS1 and Ag[Ir(ppz)2(BS1)] were used to coat commercial near-UV-emitting LEDs (395 nm). The radiant stability of the prototypes overseen for 24 h attests that the emission intensity of the Ag[Ir(ppz)2(BS1)]-LED prototype decreases only 10 %, confirming that the complex matches with the desired photostability and qualifying this complex to be used as coatings of near-UV excited white-light-emitting diodes.

Mononuclear lanthanide(III)-oxamate complexes as new photoluminescent field-induced single-molecule magnets: solid-state photophysical and magnetic properties.

Implementing additional optical (luminescent) properties into the well-known class of single-molecule magnets (SMMs) is considered as a promising route toward obtaining the next generation of optomagnetic materials for quantum information storage and computing. Herein, we report a joint optical and magneto-structural study for the two novel series of lanthanide(iii) complexes of general formula Bu4N[LnIII(HL)4(dmso)]·nH2O where H2L = N-(4-Xphenyl)oxamic acid with X = Cl and n = 2 [Ln = Eu (1_Cl), Gd (2_Cl), Dy (3_Cl), and Tb (4_Cl)] and X = F and n = 3 [Ln = Eu (1_F), Gd (2_F), Dy (3_F), and Tb (4_F)]. All these compounds are mononuclear species with each lanthanide(iii) cation in a low-symmetry nine-coordinate environment (LnO9) which is constituted by four didentate monoprotonated oxamate groups and one dmso molecule. Magnetic measurements show the occurrence of field-induced SMM behavior for the Gd3+ (2_Cl and 2_F), Dy3+ (3_Cl and 3_F), and Tb3+ complexes (4_Cl and 4_F). Solid-state photophysical measurements for the Eu3+ (1_Cl and 1_F) and Tb3+ complexes (4_Cl and 4_F) reveal that both monoprotonated chloro- and fluoro-substituted phenyl(oxamate) ligands are able to sensitize the lanthanide(iii)-based luminescence in the visible region, through an energy transfer process ("antenna effect"), as supported by theoretical calculations for Eu3+ compounds. In particular, 1_Cl and 1_F present a quantum efficiency of approximately 50%, being potentially suitable as efficient light conversion molecular devices (LCMDs).

Luminescent Eu3+–dibenzoylmethanate complex with sulfoxide ligand as sensitizer applied to organic light- emitting diodes

In this work the synthesis, characterization and photoluminescent and electroluminescent behavior of the [Eu(DBM)₃(PTSO)₂] complex have been investigated. The emission spectrum of this Eu³⁺–β– diketonate complex show characteristics narrow bands arising from the ⁵D₀→⁷Fȷ (J = 0–4) transitions, which are split according to the selection rule for Cs, Cn or Cnv site symmetries. Triple and doublelayer organic light-emitting diodes (OLEDs) using NPB as hole transporting layer, Alq₃ as electron transporting layer and [Eu(DBM)₃(PTSO)₂] complex as emitting and electron transporting layer were grown and characterized. We found the presence of two concurrent mechanisms for the electroluminescent behavior: (1) the electroluminescence (EL) from the exciton-ligand-Eu³+ ion energy transfer, responsible for the EL narrow bands; and (2) the molecular electrophosphorescence with an initial energy transfer exciton-ligand and posterior intersystem crossing from the excited singlet S₁ to the triplet T state followed by molecular phosphorescence (T→S₀). The electroluminescent behavior of [Eu(DBM)₃(PTSO)₂] complex suggest that this complex is promising to applied at Light Conversion Molecular Devices (LCMDs) such as in OLED devices.

New photo/electroluminescent europium(III) β-diketonate complex containing a p,p′-disubstituted bipyridine ligand: Synthesis, solid state characterization, theoretical and experimental spectroscopic studies

A new EuIII β-diketonate complex [Eu(btfa)3(dmbpy)] containing the btfa (4,4,4-trifluoro-1-phenyl-1,3-butanedione) and the p,p′-disubstituted bipyridine ligand dmbpy (4,4′-dimethyl-2,2′-bipyridine) have been synthesized and fully characterized. The X-ray crystal structure reveals that the compound crystallize in monoclinic system of space group P21/n, with a classical structure observed in other similar compounds. The molecular structure of the EuIII complex was calculated using the Sparkle/PM6 model, and your optimized ground state geometry were used to calculated all details involved in the energy transfer process and compared with photoluminescence experimental data. These data shows that the triplet→5D1 and triplet→5D0 are the main energy transfer channels and that the photoluminescence mechanism in this complex is proposed to be a ligand sensitized luminescence process. Additionally, red organic light emitting diode (OLED) devices were fabricated using this complex, presenting the characteristic EL emission bands due to 5D0→7FJ (J=0–4) transitions, which gives evidence that the “antenna effect” is operative. Due to its intense red photo/electroluminescence emission, this complex have potential applications as light-conversion molecular devices (LCMDs), mainly to fabricate new OLEDs.

A series of highly quantum efficiency PMMA luminescent films doped with Eu-complex as promising light-conversion molecular devices

In this paper, a series of Eu/PMMA and Eu/PMMA/SiO2 luminescent films have been designed, fabricated and characterized. Thermo-gravimetric analysis and photo-luminescence results indicated the Eu-complex precursor was successfully immobilized in PMMA matrix through the interaction between the Eu-complex and the –C=O groups of the PMMA matrix. The emission spectra of the Eu-complex and Eu/PMMA films recorded at 25 °C exhibited the characteristic bands arising from the 5D0/7FJ. The fact that the quantum efficiencies (η) of the doped film increased significantly indicated that PMMA matrix acted as an efficient co-sensitizer for Eu3+ ions luminescent center, and therefore enhanced the η of the emitter 5D0 level. Especially, with the doping nano-SiO2 into Eu/PMMA-5 % system, the T d-5 % of Eu/PMMA/SiO2 has obviously improved. Due to the carrying effect of nano-SiO2 and interaction between –C=O of PMMA chain and Eu3+ ions, the η of Eu/PMMA/SiO2 films have been greatly enhanced. To the best of our knowledge, the η of Eu/PMMA/SiO2-3 % film (78.57 %) is found to be the highest so far reported in the literature. These Eu/PMMA/SiO2 luminescent films show excellent luminescent properties and therefore have potential applications in light-conversion molecular device.

Synthesis, structure and physical properties of luminescent Pr(III) β-diketonate complexes

Near infrared lanthanide(III)-based light conversion molecular devices (LCMDs) are emerging as a promising class of materials for organic light-emitting diodes (OLEDs) in some niche technologies. Three of these molecular materials -two highly coordinated Pr3+β-diketonate monomers and a dimer- are presented and their structure and properties are discussed. Particular emphasis is placed on the solid-to-solid transformation observed for the homodinuclear compound.

Experimental and Theoretical Studies on the Structure and Photoluminescent Properties of New Mononuclear and Homodinuclear Europium(III)β-Diketonate Complexes

Two novel europium(III) complexes, a monomer and a homodimer, with 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione (Hcbtfa) and 5-chloro-1,10-phenanthroline (cphen) ligands, formulated as [Eu(cbtfa)3(cphen)] and [Eu2(cbtfa)4(cphen)2(CH3O)2], have been synthesized. Their structures have been elucidated by X-ray diffraction and their absorption and emission properties have been studied in the solid state. The experimental data has then been used to test the recently released LUMPAC software, a promising tool which can facilitate the design of more efficient lanthanide light-conversion molecular devices by combining ground state geometry, excited state energy, and luminescent properties calculations.

Mono- and dinuclear europium(III) complexes with thenoyltrifluoroacetone and 1,10-phenanthroline-5,6-dione

The N,N′-coordinated mononuclear complex Eu(TTA)3(pdn), prepared by treating 1,10-phenanthroline-5,6-dione (pdn) with Eu(TTA)3(H2O)2 (HTTA = 2-thenoyltrifluoroacetone), may be used as a benzoquinone-like ligand through the oxygen donor atoms in reaction with an additional Eu(TTA)3(H2O)2 precursor to give the dinuclear complex Eu2(TTA)6(pdn). Both the mono- and dinuclear complexes were characterized by elemental analysis, IR, TG, MS, and 1H NMR spectra. The results indicated that they both exhibited a characteristic red emission peak at 616 nm, corresponding to the 5D0 → 7F2 transition of Eu(III) ions under UV excitation. Compared with the mononuclear complex, the dinuclear complex presented better thermal stability and stronger luminescence, which makes it a promising light-conversion molecular device. .

EVA film doped with β-diketones macromolecular lanthanide complexes: Preparation, characterization and application

In this study, the β-diketones groups functionalized polymer D-HEA-C was first synthesized by chemically attaching D-HEA to the side chains of polycaprolactone and then coordinated with Eu(III) to form β-diketones macromolecular complexes. 1H NMR, FT-IR, GPC, ICP-AES, ultraviolet absorption and florescence emission were used to characterize the polymeric rare earth complex materials composed of D-HEA-C and Eu3+ ion. The synthesized β-diketones macromolecular complexes were doped into EVA film to test the energy conversion efficiency. TGA, Transmittance, UV absorption spectra, florescence emission and SEM were used to study the properties of the doped EVA film. The macromolecular complexes could not only limit the coordination of small molecules to effectively avoid the fluorescence quenching, but also enhance the fluorescence intensity of the complex. Moreover, the β-diketones macromolecular complexes have good compatibility with the EVA matrix, and could increase the photovoltaic conversion efficiency and service life of EVA film. Therefore, the β-diketones macromolecular complexes could act as efficient light conversion molecular devices, and have a broad prospect in the solar packaging film.

Luminescence enhancement by gamma irradiation of nanocomposites for UV dosimetry devices

The aim of this work is to evaluate the influence of gamma radiation on a material constituted by a photonic complex used in a UV dosimetry device embedded in a polymeric composite with multiwalled carbon nanotubes (MWCNT). Films of CNT-free and MWCNT-containing composites were exposed to a gamma radiation beam of 60Co. Characterization was performed by X-ray powder diffraction (XRD), thermogravimetric curves (TGA), and luminescence spectroscopy. The results indicate that the presented self-standing hybrid films show improvements to act as a better light conversion molecular device (LCMD) for UV dosimetry applications. Best results are attained after 50 kGy of gamma irradiation (60Co) for CNT-free composites, and 5 kGy for MWCNT-containing films.

A Comprehensive Strategy to Boost the Quantum Yield of Luminescence of Europium Complexes

Lanthanide luminescence has many important applications in anion sensing, protein recognition, nanosized phosphorescent devices, optoelectronic devices, immunoassays, etc. Luminescent europium complexes, in particular, act as light conversion molecular devices by absorbing ultraviolet (UV) light and by emitting light in the red visible spectral region. The quantum yield of luminescence is defined as the ratio of the number of photons emitted over the number of UV photons absorbed. The higher the quantum yield of luminescence, the higher the sensitivity of the application. Here we advance a conjecture that allows the design of europium complexes with higher values of quantum yields by simply increasing the diversity of good ligands coordinated to the lanthanide ion. Indeed, for the studied cases, the percent boost obtained on the quantum yield proved to be strong: of up to 81%, accompanied by faster radiative rate constants, since the emission becomes less forbidden.

Synthesis, structural characterization and photophysical properties of highly photoluminescent crystals of Eu(III), Tb(III) and Dy(III) with 2,5-thiophenedicarboxylate

Lanthanide compounds of general formula [Ln2(2,5-tdc)3(dmf)2(H2O)2]·2dmf·H2O (Ln=Eu(III) (1), Tb(III) (2), Gd(III) (3) and Dy(III) (4), dmf=N,N′-dimethylformamide and 2,5-tdc2−=2,5-thiophedicarboxylate anion) were synthesized and characterized by elemental analysis, X-ray powder diffraction patterns, thermogravimetric analysis and infrared spectroscopy. Phosphorescence data of Gd(III) complex showed that the triplet states (T1) of 2,5-tdc2− ligand have higher energy than the main emitting states of Eu(III), Tb(III) and Dy(III), indicating that 2,5-tdc2− ligand can act as intramolecular energy donor for these metal ions. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal energy transfer. The high value of experimental intensity parameter Ω2 for the Eu(III) complex indicate that the europium ion is in a highly polarizable chemical environment. The emission quantum efficiency (η) of the 5D0 emitting level of Eu(III) was also determined. The complexes act as possible light conversion molecular devices (LCMDs).

Strongly luminescent, highly ionic europium in a lanthanum diphenylphosphinate matrix

A series of insoluble, chemically inert and thermally stable compounds La1−xEux(DPP)3 (x=0.50, 0.20, 0.10, and 0.050; DPP=diphenylphosphinate) was synthesized and characterized by elemental and thermogravimetric analysis, FT Infrared spectroscopy and X-ray powder diffraction. Luminescence spectroscopy at both 77 and 298K showed changes in the intensity of the hypersensitive transition 5D0→7F2 of Eu3+ which are dependent of the excitation wavelength, suggesting that the europium occupies two different sites in the compounds. The large quantum efficiency and quantum yield, as well as the long radiative lifetime of the 5D0 Eu3+ level of the series of compounds, which are desirable qualities for light-conversion molecular devices, are discussed in terms of the interactions and the energy transfer process between the ligands and the metal ion.

Synthesis, Structure, Thermal Stability, and Magnetic and Luminescence Properties of Dinuclear Lanthanide(III) Pivalates with Chelating N‐Donor Ligands

AbstractNew dinuclear lanthanide pivalate complexes [Tb2(piv)6(Hpiv)6], [Tb2(piv)6(bpy)2], [Tb2(piv)6(phen)2], [Tb2(piv)6(bath)2]·1.5EtOH, and [Eu2(piv)6(bath)2]·2EtOH, as well as the coordination polymer {Tb(piv)3}n, in which piv = (CH3)3CCO2–, bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline, bath = 4,7‐diphenyl‐1,10‐phenanthroline, and EtOH = ethanol, were synthesized and characterized by X‐ray diffraction. For the terbium complexes, the magnetic properties and the solid‐state thermolysis were investigated. The phase composition of the solid decomposition products was determined by X‐ray powder diffraction. The photophysical properties of these complexes were analyzed by luminescence, excitation, and phosphorescence spectroscopy, and by lifetime measurements. A comparison of the photophysical data for bpy, phen, and bath complexes shows that the supramolecular organization affects the efficiency of the sensitization of Ln3+ luminescence. All the results obtained provide good prospects for the use of dinuclear lanthanide pivalate complexes as efficient light‐conversion molecular devices (LCMD).

Photophysical properties and Judd-Ofelt analysis of a europium complex with 5-amino-1,10-phenanthroline

A europium (III) complex with 5-amino-1,10-phenanthroline and 2-thenoyltrifluoroacetone, Eu(TTA) 3(phenNH 2), was synthesized. Its photophysical properties were studied in detail using UV, luminescence spectra and lifetime measurements. The complex shows a long 5D 0 lifetime (588 μs) and a remarkable luminescence quantum yield (40.95%) at room temperature, which makes it not only a promising light-conversion molecular device but also an excellent luminescent polymer precursor. Moreover, the applicability of the well-known Judd-Ofelt theory to the emissive properties of Eu 3+ complexes is also investigated.

Synthesis and characterization of a Eu-containing polymer precursor featuring thenoyltrifluoroacetone and 5-acrylamido-1,10-phenanthroline

A polymerizable ligand, 5-acrylamido-1,10-phenanthroline ( L), was synthesized. Its Eu(III) complex with 2-thenoyltrifluoroacetone (HTTA) was prepared and characterized by elemental analysis, IR, MS, and 1H NMR spectra. The photophysical properties of the complex were studied in detail by using UV, luminescence spectra, luminescence lifetime and quantum yield. The complex shows a remarkable luminescence quantum yield at room temperature (40.1%) upon ligand excitation and a long 5D 0 lifetime (590 μs), which makes it not only a promising light-conversion molecular device but also an excellent luminescent polymer precursor.

Design, synthesis and characterization of a highly luminescent Eu-complex monomer featuring thenoyltrifluoroacetone and 5-acryloxyethoxymethyl-8-hydroxyquinoline

A multi-functional ligand, 5-acryloxyethoxymethyl-8-hydroxyquinoline (Hamq), was synthesized, which contained a polymerizable C=C double bond for the copolymerization with other vinyl monomers and acted as photon antenna able to transfer energy to Eu 3+ ions effectively. The triplet state energy of Hamq was determined to be 22,370 cm −1 via the phosphorescence spectra of Hamq and its gadolinium complex. The title complex monomer Eu(tta) 2(amq) was prepared by coordination reaction of Hamq with europium isopropoxide and 2-thenoyltrifluoroacetone (Htta) in dry organic solvents under argon atmosphere and characterized by elemental analysis and IR spectrum. The photophysical properties of the complex were studied in detail with UV–vis, luminescence spectra, luminescence lifetime and quantum yield. The complex exhibited nearly monochromatic red emission at 612 nm, a remarkable luminescence quantum yield at room temperature (30.6%) upon ligand excitation and a long 5D 0 lifetime (389 μs), which indicated that the ligand Hamq could sensitize the luminescence of Eu(III) ion efficiently in Eu(tta) 2(amq), resulting in a strong luminescence of its copolymer poly[MMA- co-Eu(TTA) 2(amq)] under UV excitation. The excellent luminescence properties of the complex made it not only a promising light-conversion molecular device but also an excellent luminescent monomer.

Would the Pseudocoordination Centre Method Be Appropriate To Describe the Geometries of Lanthanide Complexes?

The correct prediction of the ground-state geometries of lanthanide complexes is an important step in the development of efficient light conversion molecular devices (LCMD). Considering this, we evaluate here the capability of semiempirical approaches and ab initio effective core potential (ECP) methodology in reproducing the coordination polyhedron geometries of lanthanide complexes. Initially, we compare the facility of two semiempirical approaches: Pseudocoordination centre method (PCC) and Sparkle model. In the first step, we considered only high-quality crystallographic structures and included 633 complexes, and in the last step, we compare the capability of two semiempirical approaches with ab initio/ECP calculations. Because this last methodology was found to be computationally very demanding, we further used a subset containing 91 high-quality crystallographic structures. A total of 91 ab initio full geometry optimizations were performed. Our results suggest that only the semiempirical Sparkle model (hundreds of times faster) present accuracy similar to what can be obtained by present-day ab initio/ECP full geometry optimization calculations on such lanthanide complexes. In addition, it further indicates that the PCC approach has a poor prediction related to the coordination polyhedron geometries of lanthanide complexes.

Synthesis, characterization and spectroscopic investigation of new tetrakis(acetylacetonato)thulate(III) complexes containing alkaline metals as countercations

In this work a series of tetrakis complexes C[Tm(acac) 4 ], where C + =Li + , Na + and K + countercations and acac=acetylacetonate ligand, were synthesized and characterized for photoluminescence investigation. The relevant aspect is that these complexes are water-free in the first coordination sphere. The emission spectra of the tetrakis Tm 3+ -complexes present narrow bands characteristic of the 1 G 4 → 3 H 6 (479 nm), 1 G 4 → 3 F 4 (650 nm) and 1 G 4 → 3 H 5 (779 nm) transitions of the Tm 3+ ion, with the blue emission color at 479 nm as the most prominent one. The lifetime values ( τ ) of the emitting 1 G 4 level of the C[Tm(acac) 4 ] complexes were 344, 360 and 400 ns for the Li + , Na + and K + countercations, respectively, showing an increasing linear behavior versus the ionic radius of the alkaline ion. An efficient intramolecular energy transfer process from the triplet state ( T ) of the ligands to the emitting 1 G 4 state of the Tm 3+ ion is observed. This fact, together with the absence of water molecules in first coordination sphere, allows these tetrakis Tm 3+ -complexes to act as efficient blue light conversion molecular devices.

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE 3+=Eu 3+, Gd 3+ and Tb 3+) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H 2O) 2], [RE(TLA)(H 2O) 4] and [RE(TMA)(H 2O) 6], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd 3+-(BTC) complexes showed that the triplet states (T) of the BTC 3− anions have energy higher than the main emitting states of the Eu 3+ ( 5D 0) and Tb 3+ ( 5D 4), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters ( Ω 2) of Eu 3+-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited 5D 0 and 5D 4 levels of the Eu 3+ and Tb 3+ ions is discussed. The emission quantum efficiencies ( η) of the 5D 0 emitting level of the Eu 3+ ion have been also determined. In the case of the Tb 3+ ion, the photoluminescence data show the high emission intensity of the characteristic transitions 5D 4→ 7F J ( J=0–6), indicating that the BTC ligands are good sensitizers. The RE 3+-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials.