Novel iridium complexes as high-efficiency yellow and red phosphorescent light emitters for organic light-emitting diodes

A series of novel biscyclometallated iridium complexes based on spirobifluorene ligands and acetyl acetonate (acac) ancillary ligands have been synthesized and characterized. Their electrochemical properties were investigated by cyclic voltammetry (CV). HOMO, LUMO, and energy band gaps of all the complexes were calculated by the combination of UV-vis absorption spectra and CV results. TGA and DSC results indicated their excellent thermal stability and amorphous structure. All the iridium complexes were fabricated into organic light-emitting devices with the device configuration of ITO/PEDOT:PSS (50 nm)/PVK (50 wt %):PBD (40 wt %):Ir complex (10 wt %) (45 nm)/TPBI (40 nm)/LiF (0.5 nm)/Ca (20 nm)/Ag (150 nm). Yellow to red light emission has been achieved from the iridium complexes guest materials. Complex C1 (yellow light emission) achieved an efficiency of 36.4 cd/A (10.1%) at 198 cd/m² and complex C4 (red light emission) reached external quantum efficiency of 4.6%. The slight decrease of external quantum efficiency at high current density revealed that the triplet-triplet (T₁-T₁) annihilation was effectively suppressed by the new developed complexes.     

A europium(II) complex with bis-pyridino-18-crown-6

A new Eu(II) complex, bis(perchlorato)(bis-pyridino-18-crown)europium(II), has been obtained in the crystalline form by electrolytic reduction. The metal ion is 10-coordinated and its surrounding consists of four macrocycle O atoms, two N ones and four O atoms from perchlorate anions. The compound shows a very broad absorption band, starting gently from 600 nm towards the UV region, and two weak luminescence bands with maxima at 430 and 500 nm. The performed density functional theory (DFT) calculations have shown that the absorption results from mixed f–d, f–s and charge transfer transitions. The possible mechanism of luminescence is also discussed.     

Photophysical properties and photostability of novel unsymmetric polycyclicphenazine-type D-π-A fluorescent dyes and the dye-doped films

Structural isomers of unsymmetric polycyclicphenazine-type D-π-A fluorescent dyes have been newly synthesized and characterized in both solution and polymer films. The dyes exhibited two strong absorption bands at around 328-401 nm and 516-532 nm, and an intense fluorescence band at around 595-629 nm (Φ = 0.32-0.84) in 1,4-dioxane. The dye-doped polymer films showed good ability of wavelength conversion; the films can efficiently convert ultraviolet and green-yellow lights into red light (Φ = 0.43-0.86). Moreover, the photostability of the dyes-doped PS, PMMA, and PLA films has been investigated.     

Highly efficient iridium(III) complexes with diphenylquinoline ligands for organic light-emitting diodes: Synthesis and effect of fluorinated substitutes on electrochemistry, photophysics and electroluminescence

A series of novel cyclometalated iridium(III) complexes bearing 2,4-diphenylquinoline ligands with fluorinated substituent were prepared and characterized by elemental analysis, NMR and mass spectroscopy. The cyclic voltammetry, absorption, emission and electroluminescent properties of these complexes were systematically investigated. Electrochemical studies showed that the oxidation of the fluorinated complexes occurred at more positive potentials (in the range 0.57-0.69 V) than the unfluorinated complex 1 (0.42 V). In view of the energy level, the lowering of the LUMO by fluorination is significantly less than that of the HOMO. The weak and low energies absorption bands in the range of 300-600 nm are well resolved, likely associated with MLCT and ³π-π^∗ transitions. These complexes show strong orange red emission both in the solution and solid state. The emission maxima of the fluorinated complexes showed blue shift by 9, 24 and 15 nm for 2, 3 and 4, respectively, with respect to the unfluorinated analogous 1. Multilayered organic light-emitting diodes (OLEDs) were fabricated by using the complexes as dopant materials. Significantly higher performance and lower turn-on voltage were achieved using the fluorinated complexes as the emitter than that using the unfluorinated counterpart 1 under the same doping level. OLED devices using complexes 2 and 3 as the phosphorescent dopant at 3 wt% doping level exhibit very high performance. To complex 2, the maximum luminance is 16 410 cd/m² at a current density of 210 mA/cm², and the maximum luminance efficiency and power efficiency are 9.34 cd/A and 5.20 lm/W, respectively, with the emission of 605 nm. To complex 3, those data are 16 797 cd/m² at a current density of 211 mA/cm², 11.12 cd/A and 4.97 lm/W, respectively, with the emission of 593 nm.     

Synthesis,One‐ and Two‐Photon Photophysical and Excited‐State Properties,and Sensing Application of a New Phosphorescent Dinuclear Cationic Iridium(III) Complex

A new phosphorescent dinuclear cationic iridium(III) complex ( Ir1 ) with a donor–acceptor–π‐bridge–acceptor–donor (D? A? π? A? D)‐conjugated oligomer ( L1 ) as a N^N ligand and a triarylboron compound as a C^N ligand has been synthesized. The photophysical and excited‐state properties of Ir1 and L1 were investigated by UV/Vis absorption spectroscopy, photoluminescence spectroscopy, and molecular‐orbital calculations, and they were compared with those of the mononuclear iridium(III) complex [Ir(Bpq)₂(bpy)]⁺PF₆^? ( Ir0 ). Compared with Ir0 , complex Ir1 shows a more‐intense optical‐absorption capability, especially in the visible‐light region. For example, complex Ir1 shows an intense absorption band that is centered at λ=448 nm with a molar extinction coefficient (ε) of about 10⁴, which is rarely observed for iridium(III) complexes. Complex Ir1 displays highly efficient orange–red phosphorescent emission with an emission wavelength of 606 nm and a quantum efficiency of 0.13 at room temperature. We also investigated the two‐photon‐absorption properties of complexes Ir0 , Ir1 , and L1 . The free ligand ( L1 ) has a relatively small two‐photon absorption cross‐section (δ_max=195 GM), but, when complexed with iridium(III) to afford dinuclear complex Ir1 , it exhibits a higher two‐photon‐absorption cross‐section than ligand L1 in the near‐infrared region and an intense two‐photon‐excited phosphorescent emission. The maximum two‐photon‐absorption cross‐section of Ir1 is 481 GM, which is also significantly larger than that of Ir0 . In addition, because the strong B? F interaction between the dimesitylboryl groups and F^? ions interrupts the extended π‐conjugation, complex Ir1 can be used as an excellent one‐ and two‐photon‐excited “ON–OFF” phosphorescent probe for F^? ions.     

Comparative spectroscopic and electrochemical properties of bis(octakis(dodecylthio)naphthalocyaninato)europium(III) and bis(tetra-tert-butylnaphthalocyaninato)europium(III) complexes

Bis(substituted-2,3-naphthalocyaninato)europium(III) complexes: bis(octakis(dodecylthio)-2,3-naphthalocyaninato)europium(III) (Eu[2,3-Nc(SC12H25)8]2, 1) and bis(tetra-tert-butyl-2,3- naphthalocyaninato)europium(III) (Eu[2,3-Nc(t-Bu)4]2, 2) have been synthesized by cyclic tetramerization of naphthalonitriles with Eu(acac)3.H2O in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in refluxing n-octanol. These compounds were characterized by UV-visible, magnetic circular dichroism (MCD), near-IR, IR, EPR, and mass spectroscopies. The absorption and MCD spectra of 1 showed splitting of the Q band, with peaks at 700 and 784 nm, red shifted from the Q band of 2 at 763 nm. The absorption and MCD spectral band deconvolution calculations of complex 1 gave two A terms in the Q-band region. The A terms are assigned to 2A2-->2E1 transitions. Cyclic voltammograms of 1 and 2 showed reversible oxidation couples at E1/2 = -0.28 V (for 2) and -0.25 V (for 1) vs ferrocenium/ferrocene (Fc+/Fc). The second oxidation exhibited a complicated behavior for both complexes. The reduction couples for 2 were observed at E1/2 = -0.61, -1.64, -1.97, and -2.42 V, and for 1 they were observed at E1/2 = -0.62, -1.60, -1.86, and -2.27 V vs Fc+/Fc. Spectral changes observed on chemical oxidation and reduction of the complexes are presented, and the behaviors of 1 and 2 are compared.     

Formation and dissociation kinetics of Eu(III) complexes with H5do3ap and similar dota-like ligands

Complexation kinetics of the europium(III)-H₅do3ap complex (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-(methylphosphonic acid)) was studied at 25 °C and I = 0.1 M KCl and compared with the analogous H₄dota-like ligands. The mechanism of the formation reactions between the europium(III) ion and H₃do3a, H₄dota and H₄dota analogs having one methylphosphonic (H₅do3ap) or phosphinic acid pendant arms with a propionate side chain (H₅do3ap^PrA) was proposed on the basis of TRLIFS measurements. The experimental data of the dissociation kinetics of the europium(III) complexes with H₅do3ap and H₅do3ap^PrA ligands show that there is no change in reactivity of the complexes due to the side chain of the phosphinic acid bifunctional chelate. The TRLIFS study of the proton-assisted decomplexation reaction of the europium(III) complexes with H₃do3a, H₄dota, H₅do3ap and H₅do3ap^PrA demonstrates different behaviour influenced by a change in the number of water molecules during the reaction. The advantages and disadvantages of the TRLIFS methodology as a new experimental technique for simultaneous evaluation of kinetics and reaction mechanisms are discussed.     

Simultaneous determination of Al(III) and Fe(III) in post-hemodialysis fluids by spectrophotometry and multivariate calibration

A multivariate calibration model (PLS) was developed for the simultaneous spectrophotometric determination of Al(III) and Fe(III) in post-hemodialysis fluids with pyrocathecol violet (PCV) as chromogenic reagent. The analytes build stable complexes with PCV in presence of hexamine buffered medium at pH 6.1. The complexes show overlapped absorption bands in the spectral range of 220-800 nm so that absorptions of 580 wavelengths were necessary for the calibrations. Determinations of Al(III) and Fe(III) were done without masking agents. The best calibration model was obtained by using PLS-1 regression with three components after data mean centering. The spectrophotometric method applied to assay the analytes in real post-hemodialysis samples containing no desferrioxamine B presented good agreement with voltammetric measurements used as reference. Concentrations ranging from 0.20 to 0.60 mg L⁻¹ for Al(III) and for Fe(III) were determined in real samples. The multivariate detection limits for Al(III) and Fe(III) were 0.044 and 0.052 mg L⁻¹, respectively, and the calculated values of sensitivity were 6.33 for Al(III) and 3.44 for Fe(III). The proposed method showed to be straightforward and useful to follow the hemodialysis progress for patients under treatment. Interferents were also investigated.     

Simultaneous capillary electrophoretic determination of Sc(III) and Y(III) based on the complex-formation with a lacunary Keggin-type [PW11O39] complex

Trace amounts of Sc(III) and Y(III) can react with [PW₁₁O₃₉]⁷⁻ to form the ternary Keggin-type complexes: [P(Sc^IIIW₁₁)O₄₀]⁶⁻ and [P(Y^IIIW₁₁)O₄₀]⁶⁻ having high molar absorptivities in the UV region. Since the rate of the complex-formation was very rapid and the kinetically stable ternary anions migrated in the capillary with different electrophoretic mobilities, the complex-formation reaction was applied to the simultaneous CE determination of Sc(III) and Y(III) with direct UV detection at 250 nm. For both Sc(III) and Y(III), the pre-column method provided linear calibration curves in the range of 2 × 10⁻⁷ to 1 × 10⁻⁵ M; the respective detection limits were 1 × 10⁻⁷ M (the signal-to-noise ratio = 3). The proposed method was successfully applied to the determination of Sc(III) and Y(III) in river water.     

Polysiloxane‐Based Luminescent Elastomers Prepared by Thiol–ene “Click” Chemistry

Side‐chain vinyl poly(dimethylsiloxane) has been modified with mercaptopropionic acid, methyl 3‐mercaptopropionate, and mercaptosuccinic acid. Coordinative bonding of Eu^III to the functionalized polysiloxanes was then carried out and crosslinked silicone elastomers were prepared by thiol–ene curing reactions of these composites. All these europium complexes could be cast to form transparent, uniform, thin elastomers with good flexibility and thermal stability. The networks were characterized by FTIR, NMR, UV/Vis, and luminescence spectroscopy as well as by scanning electron microscopy, thermogravimetric analysis, and X‐ray photoelectron spectroscopy. The europium elastomer luminophores exhibited intense red light at 617 nm under UV excitation at room temperature due to the ⁵D₀→⁷F₂ transition in Eu^III ions. The newly synthesized luminescent materials offer many advantages, including the desired mechanical flexibility. They cannot be dissolved or fused, and so they have potential for use in optical and electronic applications.     

Absorption and emission spectroscopic characterization of some azo dyes and a diamino-maleonitrile dye

A linear and nonlinear optical spectroscopic characterization is carried out on three azo dyes (Reactive orange 1, Reactive violet 8, and Acidproof purplish red), and on N-(p-hydroxybenzylidene)-diamino-maleonitrile. Fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes are measured. The saturable absorption is studied by nonlinear transmission measurements with intense picosecond laser pulses. The ground-state absorption recovery is studied by picosecond time-resolved pump and probe measurements. Absolute ground-state absorption cross-sections, excited-state absorption cross-sections, and dye concentrations are extracted from saturable absorption studies. The azo dyes have fluorescence lifetimes and ground-state absorption recovery times of around 2 ps and their excited-state absorption cross-sections are small (measured at 527 nm) making them good mode-locking dyes for picosecond and femtosecond lasers. The investigated diamino-maleonitrile dye exhibits sub-picosecond fluorescence lifetime and slow ground-state absorption recovery (>1 ns).     

Sensitive miniature single-particle immunoassay of prostate-specific antigen using time-resolved fluorescence

The present study describes the development of a quantitative miniaturized single microparticle immunoassay. The main objective of the study was to evaluate the performance of a miniature heterogeneous immunoassay on a single microparticle in respect to assay kinetics, volume, and sensitivity, binding capacity of microparticles and sensitivity using europium(III) nanoparticle labels. The performance of the single microparticle assay of prostate-specific antigen (PSA) was investigated using different-sized microparticles (60-920 μm in diameter) and microtiter well as a solid-phase. Equilibration time of the assay was shown to be dependent in a linear manner on surface-to-volume ratio, i.e. larger surface-to-volume translated to a faster reaction. However, no correlation between PSA binding capacity and equilibration time was observed in these kinetic studies. Only moderate improvement in assay kinetics was found when PSA binding capacity was increased on a microparticle. Using europium(III) nanoparticle labels, 107 nm in diameter, coated with streptavidin a detection sensitivity of 30 ng l⁻¹ (0.1 amol) was achieved in 1 μl total assay volume per microparticle. This was 50-fold higher compared to the same assay performed with intrinsically fluorescent europium(III) labels.     

Synthesis and characterization of alternative donor-acceptor arranged poly(arylene ethynylene)s derived from 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP)

A series of donor-acceptor type poly(arylene ethynylene)s (PAEs) have been synthesized through Sonogashira polycondensation. The polymers consist of an electron donating 9,9-bis(2-ethylhexyl)-9H-fluorene, triphenylamine, 1,4-dialkoxybenzene or 9-(2-ethylhexyl)-9H-carbazole unit and an electron accepting 2,5-bis(2-ethylhexyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (EH-DPP) unit, alternately connected through ethynyl bridge. The polymers exhibit weight-average molecular weights (M_w) up to 68, 500 and are soluble in chlorobenzene, dichlorobenzene, THF, chloroform and toluene. A brilliant red solution with absorption maxima between 491 and 500 nm was observed for all the polymers. An intense red fluorescent with photoemission maxima between 551 and 571 nm was observed from polymer solutions. The polymers showed good thermal stability with decomposition temperature more than 260 °C at 5% weight loss. Onset oxidation potentials of the polymers were observed between 1.30 and 1.58 V with HOMO energy levels in the range of −6.10 to −6.38 eV. The OLED devices were fabricated with configuration of ITO/PEDOT:PSS/polymer/LiF/Al for all the polymers and EL maxima between 666 and 684 nm were observed.     

脂肪酸铕配合物掺杂聚乙烯、聚丙烯和聚苯乙烯光致发光复合材料

合成了正己酸铕、正辛酸铕、月桂酸铕和硬脂酸铕4种不同碳链链长的脂肪酸铕配合物,通过哈克转矩流变仪将铕配合物(质量分数1%)机械掺杂于3种不同透明度的聚乙烯(PE)、聚丙烯(PP)和聚苯乙烯(PS)通用树脂中,制备了系列铕配合物掺杂聚合物光致发光复合材料,考察了配体、配合物、聚合物基体对复合材料的外观、透明性及其荧光性能的影响。 结果表明,4种脂肪酸铕配合物及其掺杂的复合材料在紫外光的激发下均在593、617 nm处发射强的Eu3+离子5D0→7F1、5D0→7F2跃迁的特征荧光;脂肪酸配体的碳链长短对铕配合物及复合材料的发光影响较小;PE、PP复合材料发光颜色与红光铕配合物相同,PS复合材料因基体PS和Eu3+离子的发光共同作用而呈现了玫瑰红的荧光发射。     

Photophysical properties of gatifloxacin in aqueous solution by laser flash photolysis and pulse radiolysis

GFX in water, at pH 7.0, shows intense absorption bands with peaks at 284 and 333 nm, (ε=24,670 and 12,670 M⁻¹ cm⁻¹). Both the absorption and emission properties of GFX were pH-dependent; the pK_a values for the protonation equilibria of the ground state (5.7 and 8.9) and excited singlet state (3.6 and 7.5) of GFX were determined spectroscopically. GFX fluoresces weakly, with a maximum quantum yield for fluorescence emission (0.06) at pH 4.7. A series of experiments were performed to characterize the transient species of GFX in aqueous solution using laser flash photolysis and pulse radiolysis. GFX undergoes monophotonic photoionization with a quantum yield of 0.16 on a 355 nm laser excitation. This process leads to the formation of a long-lived cation radical with a maximum absorption at 380 nm. Triplet-triplet absorption had maximum absorption at 510 nm. The reaction of GFX with one-electron oxidant N₃• was investigated and the bimolecular rate constant was determined to be 3.1×10⁹ M⁻¹ s⁻¹.     

Optical characteristics of europium and terbium doped strontium orthogermanate phosphors

In this work, europium and terbium activated Sr₂GeO₄ phosphors were successfully developed by traditional solid state method. Powders XRD, FESEM, EDS, FTIR, DRS and PL techniques have been used to probe the as prepared phosphors. Powder XRD patterns of the phosphors are indexed. The elemental composition of phosphors was obtained from their EDS. FTIR spectra are employed to detect different vibrational groups in phosphor compositions. The DRS profiles of both pristine and Eu³⁺ (Tb³⁺) substituted samples exhibit broad and strong band in the 230–370 ​nm region. The photoluminescence studies of europium and terbium doped phosphors exhibited optimistic red emission at 617 ​nm (⁵D₀ → ⁷F₂ of Eu³⁺ ions) and intense green emission at 543 ​nm (⁵D₄ → ⁷F₅ of Tb³⁺ ions) upon ultraviolet (UV) excitations respectively. The CIE chromaticity co-ordinates are produced in deep red and green regions. Therefore, these materials may become potential alternatives for red and green phosphors in the display devices and in lamp industry.     

Luminescent Properties of Europium(III) Complexes with Quinaldic Acid and Sulfur–Containing Neutral Ligands

The luminescent heteroligand complexes of europium(III) with quinaldic acid and sulfur-containing neutral ligands Eu(Quin)3∙D∙3H2O (Quin–quinaldic acid, D–dimethyl sulfoxide or dihexyl sulfoxide) and Eu(Quin)3∙3H2O have been obtained. Their composition and structure have been determined. The thermal and spectral-luminescent properties of the heteroligand europium(III) complexes have been studied. The quinaldate ion has been found to coordinate to the europium(III) ion as a bidentate ligand. The Stark structure of 5D0–7Fj (j = 0, 1, 2) transitions in the low-temperature luminescence spectra of the europium(III) complexes has been analyzed     

Red Emission of Eu(III) Complex Based on 1-(7-(tert-butyl)-9-ethyl-9H- carbazol-2-yl)-4,4,4-trifluorobutane-1,3-dione Excited by Blue Light

A new Eu(III) complex, EuL3(phen), was synthesized, where L is the abbreviation of de-protonated 1-(7-(tert-butyl)-9-ethyl-9H-carbazol-2-yl)-4,4,4-trifluorobutane-1,3-dione (HL), phen is the abbreviation of 1,10-phenanthroline. The Eu(III) complex was characterized by element analysis, IR, 1H NMR, UV-visible absorption spectroscopy, thermogravimetric anal-ysis (TGA), and photoluminescence measurements (PL). TGA shows that thermal stability of the complex is up to 325 oC. PL measurement indicates that the Eu(III) complex exhibits intense red-emission and extends their excitation bands to visible region. LEDs device was successfully fabricated by precoating complex EuL3(phen) onto 460 nm blue-emitting InGaN chip. The emission of device shows that the complex can act as red phosphor in combination with 460 nm blue-emitting chips. This europium complex based on 1-(7-(tert-butyl)-9-ethyl-9H-carbazol-2-yl)-4,4,4-trifluorobutane-1,3-dione is a kind of interesting red-emitting material excited by blue light, which could avoid the damage of excitation by UV light.     

Photochemical behavior of luminescent compositions based on antimony(III) and europium(III) complexes in high-pressure polyethylene

Luminescent and photochemical properties of polymer compositions based on the Eu(NO₃)₃(Phen)₂ complex and complexes of antimony(III) halides with diphenylguanidine are investigated. It is found that high-pressure polyethylene (HPPE) containing europium(III) and antimony(III) complexes in combination exhibits efficient transfer of electronic excitation energy from antimony(III) levels to europium(III) levels and photosensitization of europium(III) luminescence. It is shown that the europium(III) and antimony(III) complexes increase the stability of HPPE to UV radiation.     

Novel photoluminescent lanthanidomesogens forming bilayer smectic phase derived from blue light emitting liquid crystalline, one ring O-donor Schiff-base ligands

A series of new mononuclear lanthanide(III)-salicylaldimine complexes of the type [Ln(LH)₃(NO₃)₃] (Ln = La, Pr, Sm and Gd; LH = N-(2-hydroxyethyl)-4n-alkoxysalicylaldimine, n = 14, 18) have been synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, UV-Vis, FAB-mass and magnetic susceptibility measurements. The ligand (LH) coordinate to lanthanide ions in zwitterionic form via the phenolic-oxygen with the proton shifted to the imine-nitrogen. The nitrato groups occurring in chelated bidentate fashion complete a nine-coordinate geometry. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) show that the ligands are monotropic and their complexes exhibit enantiotropic highly viscous smectic A (SmA) mesophase in the temperature range 60-185 °C. A bilayer self organized assembly of the molecules in the mesophase are proposed on the basis of the small angle XRD study. The ligands are blue light emitters with a broad emission maxima at ∼447 nm while the lanthanide complexes show intense emission in the visible range (∼465-679 nm) at 350 nm excitation. The samarium(III) complex, [Sm(LH)₃(NO₃)₃] is distinct from the rest in emitting bright orange light (∼660 nm, Φ = 48%). The S_o-S₁ excitation band being stronger than the direct f-f excitation in the samarium complex clearly suggests that the Schiff-base ligands efficiently sensitize the luminescence of Sm³⁺. DFT calculations have been performed using DMol3 program at BLYP/DNP level to obtain the stable electronic structure of the ligand and complex.