Matthias Adlung

Surface-Anchored MOF-Based Photonic Antennae

The loading of a metal-organic framework (MOF), [Cu(3)(btc)(2)xH(2)O] HKUST-1, with europium β-diketonate complexes is studied with the goal to using the porous molecular framework as a photonic antenna. Whereas loading of HKUST-1 powder particles produced via the conventional solvothermal synthesis method was strongly hindered, for HKUST-1 SURMOFs, thin MOF films fabricated using the liquid phase epitaxy method, a high filling factor can be achieved. The optical properties of the HKUST-1-MOFs before and after loading were analysed with the aid of luminescence spectroscopy. Careful analysis of the absorption spectra reveals the presence of an effective energy transfer between the HKUST-1 framework and the Eu(3+) centers.

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu-II(Cp-BIG)(2)] (Cp-BIG=(4-nBu-C6H4)(5)-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu[superscript II](Cp[superscript BIG])[subscript 2]] (Cp[superscript BIG]=(4-nBu-C[subscript 6]H[subscript 4])[subscript 5]-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Syntheses, structures and luminescence properties of novel metal–organic frameworks based on zinc(II), cadmium(II) or lead(II) and a 2,2′-dimethoxy-functionalised biphenyl linker

Three metal–organic frameworks (MOFs) based on zinc(II) (1), cadmium(II) (2) or lead(II) (3) and the functionalised biphenyl linker biphenyl-2,2′-dimethoxy-4,4′-dicarboxylate, [4,4′-(CO2)2-2,2′-(OMe)2-1,1′-(C6H3)2] (L), were synthesised. Compounds 1 and 3 exhibit different three-dimensional networks with the Zn4O(O2C)6(H2O) unit as the secondary building unit (SBU) in the Zn-based MOF [{(Zn4O)(L)3(H2O)}·4.5DMF]n (1) and Pb6O2(O2C)4 clusters as SBU in the Pb-based MOF [{(Pb6O2)L4}·2EtOH]n (3), as shown by X-ray analysis. The Cd-based MOF [{(Cd3L4)2(CdL2)}·8DMF·8Me2NH2·2Cl]n (2) exhibits two interpenetrated three-dimensional networks formed from two different types of secondary building units, Cd3(μ-O2C)6(O2C)2 and Cd(O2C)4. Compounds 1–3 are thermally stable up to 420, 360 and 380 °C, respectively (according to DTA–TG). All compounds show bluish emissions visible with the naked eye, which could be assigned to S1,2 → S0 transitions of the aromatic units by comparison with the luminescence properties of the free ligand.

Novel sol-gel precursors for thin mesoporous eu(3+)-doped silica coatings as efficient luminescent materials.

Europium(III) ions containing mesoporous silica coatings have been prepared via a solvent evaporation-induced self-assembly (EISA) approach of different single-source precursors (SSPs) in the presence of Pluronic P123 as a structure-directing agent, using the spin-coating process. A deliberate tailoring of the chemical composition of the porous coatings with various Si:Eu ratios was achieved by processing mixtures of tetraethylorthosilicate (TEOS) and Eu3+-coordinated SSPs. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses demonstrate that the thin metal oxide-doped silica coatings consist of a porous network with a short-range order of the pore structure, even at high europium(III) loadings. Furthermore, luminescence properties were investigated at different temperatures and different degrees of Eu3+ contents. The photoluminescence spectra clearly show characteristic emission peaks corresponding to the 5D0 → 7FJ (J = 0–5) transitions resulting in a red luminescence visible by the eyes, although the films have a very low thickness (150–200 nm).

Allylamine-mediated DNA attachment to polycrystalline diamond surface

Allylamine, an unsaturated short carbon chain amine was used to mediate ss-DNA attachment to an H-terminated polycrystalline diamond thin film surface for biosensoric applications. At first, allylamine was photochemically tethered onto the diamond film surface; ss-DNA was then attached via the allylamine linkage. The DNA molecules are then hybridized with the complementary DNA molecules containing fluorescence labels followed by denaturing. Time-of-fight secondary ion mass spectrometry and fluorescence spectroscopy are used to confirm the allylamine bonding and the covalent DNA bonding to the diamond film surface, respectively.

SrAl2O4:Eu2+(,Dy3+) Nanosized Particles: Synthesis and Interpretation of Temperature-Dependent Optical Properties

SrAl 2 O 4 nanosized particles (NPs) undoped as well as doped with Eu and Dy were prepared by combustion synthesis for the discussion of their intensively debated spectroscopic properties. Emission spectra of SrAl 2 O 4 :Eu(,Dy) NPs are composed by a green band at 19 230 cm (520 nm) at room temperature, assigned to anomalous luminescence originated by Eu in this host lattice. At low temperatures, a blue emission band at 22 520 cm (444 nm) is observed. Contrary to most of the interpretations provided in the literature, we assign this blue emission band very reliably to a normal 4f(F J )5d(t 2g)→ 4f (S 7/2 ) transition of Eu substituting the Sr sites. This can be justified by the presence of a fine structure in the excitation spectra due to the different 7FJ levels (J = 0 ⋅ ⋅ ⋅ 6) of the 4f core.Moreover, Fano antiresonances with the 6IJ (J = 9/2, 7/2) levels could be observed. In addition, the Stokes shifts (ΔE S = 1 980 cm and 5 270 cm for the blue and green emission, resp.), the Huang-Rhys parameters of S = 2.5 and 6, and the average phonon energies of ħω = 480 cm and 470 cm coupled with the electronic states could be reliably determined.

Synthesis of highly stable magnesium fluoride suspensions and their application in the corrosion protection of a Magnesium alloy

This study presents a new approach to enhance the corrosion resistance of tungsten inert gas (TIG) welded AZ31 magnesium alloys by using nanocrystalline magnesium fluoride suspensions in a suspension plasma spray (SPS) process. We have developed a synthesis for the preparation of nanocrystalline magnesium fluoride suspensions, which delivers nearly monodisperse nanoparticles in a gram scale yield. The particles were analyzed with transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD). Stable suspensions of magnesium fluoride nanoparticles in water were characterized by dynamic light scattering (DLS), zeta-potential, and viscosity measurements. Such suspensions were deposited with an SPS torch onto TIG welded seams of the magnesium alloy AZ31, thus producing a protective magnesium fluoride layer. Magnesium fluoride covered welded seams were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDXS). In order to introduce a simple method for sensoring the deposited magnesium fluoride coatings, the magnesium fluoride nanoparticles can also be fluorescence-labeled by co-doping with cerium(III) and terbium(III), the respective optical properties were characterized by reflection and luminescence spectroscopy. The deposited layers can, thus, be inspected by illumination with an UV lamp, because of their bright green emission. The corrosion properties of the magnesium fluoride layer on the welded seams were studied by means of potentiodynamic potential measurements.

ABiO2X (A = Cd, Ca, Sr, Ba, Pb; X = halogen) Sillen X1 Series: Polymorphism Versus Optical Properties

The Sillen X1 series of Bi(3+)A(2+)O2X (A = Cd, Ca, Sr, Ba, Pb; X = Cl, Br, I) compounds is composed of three main crystallographic types, namely, the tetragonal form (space group (S.G.) I4/mmm), the orthorhombic form (S.G. Cmcm), and the monoclinic form (S.G. P21/m). Because of Bi(3+)/A(2+) disorder the Bi(3+) based photoluminescence (PL) of the tetragonal polytypes is quenched at room temperature (RT). In the two other ordered forms, the Bi-O-Bi connectivity is different but limited, such that bluish/greenish emission occurs at RT in the monoclinic CdBiO2Cl and CaBiO2Cl and orthorhombic SrBiO2Cl and BaBiO2Cl phases. The crystal structure of BaBiO2Br was refined in the orthorhombic Cmcm space group and also shows RT emission. Focusing on the RT luminescent activity as a key parameter, the PL active compounds were investigated by means of density functional theory calculations and UV-visible reflectance spectroscopy. The influence of A and X ions on the excitation energy is discussed by analyzing the A-O-Bi and Bi-X bonding schemes and gives some insights for rational tuning of both the excitation and emission energies.

Oscillating Emission of [2]Rotaxane Driven by Chemical Fuel

A molecular shuttle consisting of a dibenzo-24-crown-8 macrocycle and an axle with two degenerate peripheral triazolium stations, a central dibenzyl ammonium station, and two anthracenes stoppers was exposed to 2-cyano-2-phenylpropanoic acid as a chemical fuel. Protonation/deprotonation of the amine reversibly switches the rotaxane from a static and little emissive to a dynamic fluorescent shuttling device, the latter exhibiting rapid motion (15 kHz at 25 °C). Four fuel cycles were run.