Optically hybrid lanthanide ions (Eu3+, Tb3+)‐centered materials with novel functional di‐urea linkages

The synthesis of 3‐(triethoxysilyl)‐propyl isocyanate (TEPIC) modified by (3‐aminopropyl)triethoxysilane (APS) and the preparation of the corresponding organic–inorganic molecular‐based hybrid material with the two components equipped with covalent bonds is described. The coupling agent moiety is a convolution of TEPIC and APS through ? NHC(?O)NH? groups, which is applied to coordinate to RE³⁺ and further formed Si? O backbones after hydrolysis and polycondensation processes. For comparison and luminescence efficiency purposes, we added 2,2‐bipyridyl to the above hybrids in order to increase the conjugating effects and sensitize rare earth ions emissions. Luminescence spectra were utilized to characterize the photophysical properties of the hybrid material obtained, and the above spectroscopic data reveal that the triplet energy of 2,2‐dipyridyl in this favorable hybrid system matches with the emissive energy level of RE³⁺. In this way, the intramolecular energy transfer process took place within these molecular‐based hybrids and strong green and red emissions of RE³⁺ have been achieved. Copyright © 2005 John Wiley & Sons, Ltd.     

Functional Mesoporous Material Derived from 3D Net‐Linked SBA‐15

Caught in the net : Zirconia‐modified SBA‐15 mesoporous silica with a specific 3D net‐linked morphology (see picture) is prepared by using a facile method. This new functional material can trap particles in tobacco smoke and so can be applied towards environmental protection.

     

Synthesis of Olive‐Shaped Mesoporous Platinum Nanoparticles (MPNs) with a Hard‐Templating Method Using Mesoporous Silica (SBA‐15)

Well‐ordered mesoporous Pt nanoparticles (MPNs) with uniform olive shapes are synthesized by using two‐dimensional (2D) hexagonal mesoporous silica (SBA‐15) as a hard template. The average particle sizes are controllable in the range of 150 to 230 nm by changing the reduction time. Low‐angle XRD profiles for the obtained MPNs show three distinct peaks assignable to the (10), (11), and (20) planes of a highly ordered 2D hexagonal symmetry. From high‐magnification SEM images, periodically arranged Pt nanowires are observed clearly, which are a negative replica of the 2D hexagonally ordered mesoporous silica (SBA‐15). Furthermore, the single crystallinity of the Pt fcc structure coherently extends over the whole particles. As a result of such unique character as well as high surface area, the obtained MPNs show distinctly enhanced electrocatalytic properties for methanol oxidation reaction compared to other Pt samples, such as Pt black.     

Lanthanide(III) (Eu,Gd, Tb,Dy) Complexes Derived from 4‐(Pyridin‐2‐yl)methyleneamino‐1,2,4‐triazole: Crystal Structure,Magnetic Properties,and Photoluminescence

The reaction of lanthanide(III) nitrates with 4‐(pyridin‐2‐yl)methyleneamino‐1,2,4‐triazole (L) was studied. The compounds [Ln(NO₃)₃(H₂O)₃] ? 2 L, in which Ln=Eu ( 1 ), Gd ( 2 ), Tb ( 3 ), or Dy ( 4 ), obtained in a mixture of MeCN/EtOH have the same structure, as shown by XRD. In the crystals of these compounds, the mononuclear complex units [Ln(NO₃)₃(H₂O)₃] are linked to L molecules through intermolecular hydrogen‐bonding interactions to form a 2D polymeric supramolecular architecture. An investigation into the optical characteristics of the Eu³⁺‐, Tb³⁺‐, and Dy³⁺‐containing compounds ( 1 , 3 , and 4 ) showed that these complexes displayed metal‐centered luminescence. According to magnetic measurements, compound 4 exhibits single‐ion magnet behavior, with ΔE_eff/k_B=86 K in a field of 1500 Oe.     

Facile Synthesis of Lanthanide (Ce,Eu, Tb,Ce/Tb,Yb/Er,Yb/Ho,and Yb/Tm)‐Doped LnF3 and LnOF Porous Sub‐Microspheres with Multicolor Emissions

Monodisperse YF₃ and YOF porous sub‐microspheres were synthesized by using a novel sacrificing template method with amorphous Y(OH)CO₃ ⋅ x H₂O as the precursors and the template. It was found that the size and shape were well maintained, and the condensed precursor was transformed into uniform porous structures after fluoridation. By fine‐tuning the feed of the fluorine source, the final product could be converted from YF₃ to YOF. A possible growth mechanism is proposed for the uniform porous YF₃ structure and the porous yolk–shell‐like YOF structure. The luminescence properties showed that the as‐synthesized YF₃:Ln³⁺ (Ln=Eu, Tb, Ce, Ce/Tb, Yb/Er, Yb/Ho, and Yb/Tm) products exhibited strong multicolor emissions, which included down‐/upconversion and energy‐transfer processes. Additionally, YOX (X=Cl and Br) could be obtained if a different halogen source was used during calcination. However, the spheres were almost completely destroyed. Our novel synthetic route can also be extended to other lanthanide fluorides (REF₃, RE=Gd, Lu), which may open a facile way to fabricate novel porous nanostructures.     

Red‐NIR Luminescent Hybrid Poly(methyl methacrylate) Containing Covalently Linked Octahedral Rhenium Metallic Clusters

The embedding of functional inorganic entities into polymer matrices has become an intense field of investigation in which the main challenges are to keep the added value of the inorganic entities while preventing their self‐aggregation within the organic matrix. We present a simple way to obtain a homogeneous highly red‐NIR luminescent hybrid copolymer that contains covalently bonded nanometric‐sized {Re₆} octahedral clusters. The [Re₆Seⁱ₈(OH)^a₆]^4? cluster complexes are primarily functionalized in two steps with tert‐butylpyridine (TBP) and methacrylic acid (MAC) to give neutral [Re₆Se₈(TBP)₄(MAC)₂] building blocks that are copolymerized with methyl methacrylate (MMA) either in solution or in bulk in the presence of azobisisobutyronitrile as an initiator. Several samples containing 0, 0.025, 0.05, and 0.1 wt % of functionalized {Re₆} clusters were prepared. As the {Re₆} cluster/MMA ratio is very low, the obtained copolymers keep the entire processability of pure poly(methyl methacrylate) (PMMA), as demonstrated by differential scanning calorimetry and thermogravimetric analysis. Voltammetric and luminescence studies also indicate that the intrinsic properties of the clusters are preserved within the polymer matrix. All the samples show a bright (emission quantum yield=0.07), broad, and structureless emission band, which extends from λ=600 nm to more than λ=950 nm, with the maximum wavelength centered around λ_em=710 nm either in solution or in the solid state. Moreover, the high stability of the incorporated inorganic phosphors prevents the material from photobleaching, and thus the luminescence properties are kept entirely even after nine months of ageing.     

Lanthanide Luminescence Improvement by Using a Functional Poly(Ionic Liquid) as Matrix and Co‐ligand

A poly(ionic liquid) (BA‐PIL) carrying a benzoic acid group in each repeating unit of the polymer architecture, which has the dual function of acting as a matrix and second ligand, has been developed. Through the incorporation of BA‐PIL with the complex [Ln(hfa)₃] (hfa=hexafluoroacetylacetone) as an emitting precursor, significant luminescence improvement was achieved in the obtained hybrid materials. Confinement of the lanthanide(III) complexes within the rigid chains of the polymer, together with replacement of the coordinated water molecules, are believed to be ascribed to the enhanced optical properties.     

Directional Study of the Optical Properties of Tb3+‐ and Eu3+‐Doped Nanoparticles Embedded in Silica Photonic Crystals

The effects of the stop band (SB) in colloidal photonic crystals composed of silica spheres containing Eu³⁺‐ and Tb³⁺‐doped yttria nanoparticles are analysed. Reflection and transmission spectra indicate movement of the stop band, due to the 111 series of planes, towards shorter wavelengths with increasing angle of observation. The profile of the emission spectra is modified by the presence of the SB depending on the angle of measurement. Such a modification is more effective for a narrow emission band and it is thus more evident in the case of Tb³⁺ than Eu³⁺. An angular effect is also observed in the lifetime, which presents two maxima and one minimum. In the case of Tb³⁺ the maxima are at observation angles of 35 and 50°, and the minimum at 45°. We attribute this behaviour to penetration of the excitation beam at 475 nm modulated by the stop band. The ions excited in this way emit from different depths in the crystal, and therefore their lifetime will be affected differently by the same stop band, depending on the thickness of the crystal that must be crossed. Eu³⁺ shows a similar but less pronounced effect for two reasons: first, the main stop band (due to the 111 planes) is not effective at the excitation wavelength of 392 nm; second, the broadness of the Eu³⁺ emission is comparable to the width of the SB, and a decrease in the transition rate at the wavelength of the SB maximum is compensated by an increase at the sides of the SB.     

Poly(arginine)‐Selective Coprecipitation Properties of Self‐Assembling Apoferritin and Its Tb3+ Complex: A New Luminescent Biotool for Sensing of Poly(arginine) and Its Protein Conjugates

The apoferritin protein and apoferritin–Tb³⁺ complex were demonstrated to form oligomeric and polymeric self‐assemblies in neutral aqueous solutions, based on characterization by using luminescence and UV/Vis spectroscopy, dynamic light scattering, and transmission electron microscopy. Addition of a 20‐mer or higher poly(arginine) to the solution resulted in coprecipitation through nanoscale interactions, while biological proteins and other poly(amino acids) rarely yielded precipitates under the conditions employed. The apoferritin–Tb³⁺ complex assembly exhibited a particularly long‐lived green luminescence in aqueous solution, and its poly(arginine)‐selective precipitation behavior was followed by monitoring the changes in luminescence. The poly(arginine)‐tagged albumin precipitated selectively and quantitatively, so that the apoferritin–Tb³⁺ complex can function as a new luminescent biotool for the sensing of poly(arginine) and its protein conjugates.     

Ytterbium(III) Porpholactones: β‐Lactonization of Porphyrin Ligands Enhances Sensitization Efficiency of Lanthanide Near‐Infrared Luminescence

The near‐infrared (NIR) luminescence efficiency of lanthanide complexes is largely dependent on the electronic and photophysical properties of antenna ligands. Although porphyrin ligands are efficient sensitizers of lanthanide NIR luminescence, non‐pyrrolic porphyrin analogues, which have unusual symmetry and electronic states, have been much less studied. In this work, we used porpholactones, a class of β‐pyrrolic‐modified porphyrins, as ligands and investigated the photophysical properties of lanthanide porpholactones Yb‐1 a – 5 a . Compared with Yb porphyrin complexes, the porpholactone complexes displayed remarkable enhancement of NIR emission (50–120 %). Estimating the triplet‐state levels of porphyrin and porpholactone in Gd complexes revealed that β‐lactonization of porphyrinic ligands lowers the ligand T₁ state and results in a narrow energy gap between this state and the lowest excited state of Yb³⁺. Transient absorption spectra showed that Yb^III porpholactone has a longer transient decay lifetime at the Soret band than the porphyrin analogue (30.8 versus 17.0 μs). Thus, the narrower energy gap and longer lifetime arising from β‐lactonization are assumed to enhance NIR emission of Yb porpholactones. To demonstrate the potential applications of Yb porpholactone, a water‐soluble Yb bioprobe was constructed by conjugating glucose to Yb ‐ 1 a . Interestingly, the NIR emission of this Yb porpholactone could be specifically switched on in the presence of glucose oxidase and then switched off by addition of glucose. This is the first demonstration that non‐pyrrolic porphyrin ligands enhance the sensitization efficiency of lanthanide luminescence and also display switchable NIR emission in the region of biological analytes (800–1400 nm).     

Photoactive Hybrid Materials of Lanthanide (Eu3+, Tb3+, Sm3+) Beta‐Diketonates and Polymer Resin Through Ionic Liquid Bridge

A special multifunctional ionic liquid compound (1‐methyl‐3‐(2‐(thiocarboxyoxy)‐ethyl)‐2H‐imidazole‐1,3‐diium bromide (SHIL)) is used as the chemical bridge to link lanthanide beta‐diketonates and polymer resin, which are designated as Ln(L)₄‐SHIL‐WR/MR (Ln = Eu, Tb, Sm; L = thenoyltrifluoroacetonate (TTA), acetylacetonate (AA), dibenzoylmethane (DBM); WR = Wang resin, MR = Merrifield resin). Among SHIL and polymer resin are assembled to form covalently bonded system through condensation reaction. Then tetrakis lanthanide beta‐diketonates are linked to SHIL through ion‐exchange reaction. Physical characterization and especially the photoluminescent performance of the multicomponent hybrids are studied. The hybrid materials possess good stability and excellent luminescent property. The results provide useful path to obtain luminescent hybrids for further practical application.     

Synthesis and Luminescence of Eu‐N2,N6‐Bis(2‐hydroxyethyl)pyridine‐2,6‐dicarboxamide Complexes Containing Mesoporous Material

Ligand N²,N⁶‐bis(2‐hydroxyethyl)pyridine‐2,6‐dicarboxamide (L=BHPC) was synthesized and used to construct lanthanide‐based mesoporous material Eu‐L‐MCM‐41. In the structure of resulting Eu‐L‐MCM‐41, Eu³⁺ was chelated by BHPC, and the Eu‐L complexes were anchored into the forming MCM‐41 host by the reaction between the hydroxyl group and active Si‐OH. The mesoporous material Eu‐L‐MCM‐41 was characterized by UV, IR, small‐angle X‐ray diffraction (SAXRD) patterns, nitrogen adsorption/desorption isotherms, TGA and fluorescence spectra. The results indicate that ligand and Eu³⁺ have been introduced into the MCM‐41 host, and Eu‐L‐MCM‐41 exhibits characteristic luminescence of Eu³⁺.     

Synthesis,Persistent Luminescence,and Thermoluminescence Properties of Yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce,Nd, Dy,Ho, Er,Tm, Yb) and Orange‐Red Sr3−xBaxSiO5:Eu2+, Dy3+ Phosphor

Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu²⁺ in Sr₃SiO₅ was significantly modified. The yellow persistent emission intensity of Eu²⁺ was greatly enhanced by a factor of 4.5 in Sr₃SiO₅:Eu²⁺,Nd³⁺ compared with the previously reported Sr₃SiO₅:Eu²⁺, Dy³⁺. Furthermore, Sr ions were replaced with equivalent Ba to give Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu²⁺ is significantly improved by a factor of 2.7 in Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ (x=0.2) compared with Sr₃SiO₅:Eu²⁺,Dy³⁺. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu²⁺ in Sr_3?xBa_xSiO₅:Eu²⁺,RE³⁺ (RE=rare earth) is also proposed and discussed.     

Experimental and Theoretical Studies on the Magnetic Anisotropy in Lanthanide(III)‐Centered Fe3Ln Propellers

Compounds [Fe₃Ln(tea)₂(dpm)₆] ( Fe₃Ln ; Ln= Tb–Yb, H₃tea=triethanolamine, Hdpm=dipivaloylmethane) were synthesized as lanthanide(III)‐centered variants of tetrairon(III) single‐molecule magnets (Fe₄) and isolated in crystalline form. Compounds with Ln=Tb–Tm are isomorphous and show crystallographic threefold symmetry. The coordination environment of the rare earth, given by two tea^3? ligands, can be described as a bicapped distorted trigonal prism with D₃ symmetry. Magnetic measurements showed the presence of weak ferromagnetic Fe ??? Ln interactions for derivatives with Tb, Dy, Ho, and Er, and of weak antiferromagnetic or negligible coupling in complexes with Tm and Yb. Alternating current susceptibility measurements showed simple paramagnetic behavior down to 1.8 K and for frequencies reaching 10000 Hz, despite the easy‐axis magnetic anisotropy found in Fe₃Dy , Fe₃Er , and Fe₃Tm by single‐crystal angle‐resolved magnetometry. Relativistic quantum chemistry calculations were performed on Fe₃Ln (Ln=Tb–Tm): the ground J multiplet of Ln³⁺ ion is split by the crystal field to give a ground singlet state for Tb and Tm, and a doublet for Dy, Ho, and Er with a large admixture of m_J states. Gyromagnetic factors result in no predominance of g_z component along the threefold axis, with comparable g_x and g_y values in all compounds. It follows that the environment provided by the tea^3? ligands, though uniaxial, is unsuitable to promote slow magnetic relaxation in Fe₃Ln species.     

Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone,Bearing Pyrazole Moiety and CHF2-Group: Structure,Color Tuning,and Kinetics of Energy Transfer between Lanthanide Ions

Three novel lanthanide complexes with the ligand 4,4-difluoro-1-(1,5-dimethyl-1H-pyrazol-4-yl)butane-1,3-dione (HL), namely [LnL₃(H₂O)₂], Ln = Eu, Gd and Tb, were synthesized, and, according to single-crystal X-ray diffraction, are isostructural. The photoluminescent properties of these compounds, as well as of three series of mixed metal complexes [Eu_xTb_1-xL₃(H₂O)₂] (Eu_xTb_1-xL₃), [EuxGd_1-xL₃(H₂O)₂] (Eu_xGd_1-xL₃), and [Gd_xTb_1-xL₃(H₂O)₂] (Gd_xTb_1-xL₃), were studied. The Eu_xTb_1-xL₃ complexes exhibit the simultaneous emission of both Eu³⁺ and Tb³⁺ ions, and the luminescence color rapidly changes from green to red upon introducing even a small fraction of Eu³⁺. A detailed analysis of the luminescence decay made it possible to determine the observed radiative lifetimes of Tb³⁺ and Eu³⁺ and estimate the rate of excitation energy transfer between these ions. For this task, a simple approximation function was proposed. The values of the energy transfer rates determined independently from the luminescence decays of terbium(III) and europium(III) ions show a good correlation.     

Metal‐Ion Permeation in Congested Nanochannels: The Exposure Effect of Ag+ Ions on the Phosphorescent Properties of a Gold(I)–Pyrazolate Complex that is Confined in the Nanoscopic Channels of Mesoporous Silica

An organometallic/silica nanocomposite of a 1D cylindrical assembly of a trinuclear gold(I)–pyrazolate complex ([Au₃Pz₃]) that was confined inside the nanoscopic channels of hexagonal mesoporous silica ([Au₃Pz₃]/silica_hex), emitted red light with a luminescence center at 693 nm upon photoexcitation at 276 nm owing to a Au^I? Au^I metallophilic interaction. When a film of [Au₃Pz₃]/silica_hex was dipped into a solution of Ag⁺ in tetrahydrofuran (THF), the resulting nanocomposite material (Ag@[Au₃Pz₃]/silica_hex) emitted green light with a new luminescence center at 486 nm, which was characteristic of a Au^I? Ag^I heterometallic interaction. Changes in the emission/excitation and XPS spectra of Ag@[Au₃Pz₃]/silica_hex revealed that Ag⁺ ions permeated into the congested nanochannels of [Au₃Pz₃]/silica_hex, which were filled with the cylindrical assembly of [Au₃Pz₃].     

Mesoporous Silica Particles as Topologically Crosslinking Fillers for Poly(N‐isopropylacrylamide) Hydrogels

Here it is demonstrated that mesoporous silicas (MPSs) can be used as effective “topological crosslinkers” for poly(N‐isopropylacrylamide) (PNIPA) hydrogels to improve the mechanical property. Three‐dimensional bicontinuous mesporous silica is found to effectively reinforce the PNIPA hydrogels, as compared to nonporous silica and two‐dimensional hexagonally ordered mesoporous silica.     

Learning from a Mineral Structure toward an Ultra‐Narrow‐Band Blue‐Emitting Silicate Phosphor RbNa3(Li3SiO4)4:Eu2+

Learning from natural mineral structures is an efficient way to develop potential host lattices for applications in phosphor converted (pc)LEDs. A narrow‐band blue‐emitting silicate phosphor, RbNa₃(Li₃SiO₄)₄:Eu²⁺ (RNLSO:Eu²⁺), was derived from the UCr₄C₄‐type mineral model. The broad excitation spectrum (320–440 nm) indicates this phosphor can be well matched with the near ultraviolet (n‐UV) LED chip. Owing to the UCr₄C₄‐type highly condensed and rigid framework, RNLSO:Eu²⁺ exhibits an extremely small Stokes shift and an unprecedented ultra‐narrow (full‐width at half‐maximum, FWHM=22.4 nm) blue emission band (λ_em=471 nm) as well as excellent thermal stability (96 %@150 °C of the initial integrated intensity at 25 °C). The color gamut of the as‐fabricated (pc)LEDs is 75 % NTSC for the application in liquid crystal displays from the prototype design of an n‐UV LED chip and the narrow‐band RNLSO:Eu²⁺ (blue), β‐SiAlON:Eu²⁺ (green), and K₂SiF₆:Mn⁴⁺ (red) components as RGB emitters.     

Synthesis and luminescence of yellow/orange‐emitting poly[tris(2,5‐dihexyloxy‐1,4‐phenylenevinylene)‐ alt‐(1,3‐phenylenevinylene)]s

Soluble yellow/orange‐emitting poly[tris(2,5‐dihexyloxy‐1,4‐phenylenevinylene)‐alt‐(1,3‐phenylenevinylene)] derivatives ( 6 ) were synthesized and characterized. These polymers contained oligo(p‐phenylene vinylene) chromophores of equal conjugation length, which were jointed via a common m‐phenylene unit. An optical comparison of 6 and its model compound ( 8 ) at room temperature and low temperatures revealed the similarity in their absorption and fluorescence band structures. The vibronic band structure of 6 was assigned with the aid of the spectroscopic data for 8 at the low temperatures. 6 was electroluminescent and had an emission maximum wavelength at approximately 565 nm. With the device indium tin oxide/PEDOT/ 6 /Ca configuration, the polymer exhibited an external quantum efficiency as high as 0.25%. Simple substitution on m‐phenylene of 6 raised the electroluminescence output by a factor of about 10. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5853–5862, 2004