Luminescence properties and quenching mechanisms of Ln(Tf2N)3 complexes in the ionic liquid bmpyr Tf2N

The emission properties, including luminescence lifetimes, of the lanthanide complexes Ln(Tf(2)N)(3) (Tf(2)N = bis(trifluoromethanesulfonyl)amide); Ln(3+) = Eu(3+), Tm(3+), Dy(3+), Sm(3+), Pr(3+), Nd(3+), Er(3+)) in the ionic liquid bmpyr Tf(2)N (bmpyr = 1-n-butyl-1-methylpyrrolidinium) are presented. The luminescence quantum efficiencies, η, and radiative lifetimes, τ(R), are determined for Eu(3+)((5)D(0)), Tm(3+)((1)D(2)), Dy(3+)((4)F(9/2)), Sm(3+)((4)G(5/2)), and Pr(3+)((3)P(0)) emission. The luminescence lifetimes in these systems are remarkably long compared to values typically reported for Ln(3+) complexes in solution, reflecting weak vibrational quenching. The 1.5 μm emission corresponding to the Er(3+) ((4)I(13/2)→(4)I(15/2)) transition, for example, exhibits a lifetime of 77 μs. The multiphonon relaxation rate constants are determined for 10 different Ln(3+) emitting states, and the trend in multiphonon relaxation is analyzed in terms of the energy gap law. The energy gap law does describe the general trend in multiphonon relaxation, but deviations from the trend are much larger than those normally observed for crystal systems. The parameters determined from the energy gap law analysis are consistent with those reported for crystalline hosts. Because Ln(3+) emission is known to be particularly sensitive to quenching by water in bmpyr Tf(2)N, the binding properties of water to Eu(3+) in solutions of Eu(Tf(2)N)(3) in bmpyr Tf(2)N have been quantified. It is observed that water introduced into these systems binds quantitatively to Ln(3+). It is demonstrated that Eu(Tf(2)N)(3) can be used as a reasonable internal standard, both for monitoring the dryness of the solutions and for estimating the quantum efficiencies and radiative lifetimes for visible-emitting [Ln(Tf(2)N)(x)](3-x) complexes in bmpyr Tf(2)N.     

Degenerate Two‐Photon Absorption and Effective Optical‐Power‐Limiting Properties of Multipolar Chromophores Derived from 2,3,8‐Trisubstituted Indenoquinoxaline

Two analogous multipolar chromophores ( 1 and 2 ) that contained 2,3,8‐trisubstituted indenoquinoxaline moieties have been synthesized and characterized for their two‐photon absorption properties, both in the femtosecond and nanosecond time regimes. We demonstrated that their multi‐branched framework structures, which incorporated appropriately functionalized indenoquinoxaline units, afforded large molecular nonlinear absorptivities within the studied spectroscopic range. Effective optical‐power‐limiting and stabilization behaviors in the nanosecond regime of dye molecule ( 2 ) were also investigated and the results indicated that such a structural motif could be a useful approach to the molecular design of highly active two‐photon systems for quick‐response and related broadband optical‐suppressing applications, in particular for confronting laser pulses of a long duration.     

Strategic Capture of the {Nb7} Polyoxometalate

Group V Nb-polyoxometalate (Nb-POM) chemistry generally lacks the elegant pH-controlled speciation exhibited by group VI (Mo, W) POM chemistry. Here three Nb-POM clusters were isolated and structurally characterized; [Nb₁₄O₄₀(O₂)₂H₃]¹⁴⁻, [((UO₂)(H₂O))₃Nb₄₆(UO₂)₂O₁₃₆H₈(H₂O)₄]²⁴⁻, and [(Nb₇O₂₂H₂)₄(UO₂)₇(H₂O)₆]²²⁻, that effectively capture the aqueous Nb-POM species from pH 7 to pH 10. These Nb-POMs illustrate a reaction pathway for control over speciation that is driven by counter-cations (Li⁺) rather than pH. The two reported heterometallic POMs (with UO₂²⁺ moieties) are stabilized by replacing labile H₂O/HO−Nb=O with very stable O=U=O. The third isolated Nb-POM features cis-yl-oxos, prior observed only in group VI POM chemistry. Moreover, with these actinide-heterometal contributions to the burgeoning Nb-POM family, it now transects all major metal groups of the periodic table.     

Discrete Hf18 Metal‐oxo Cluster as a Heterogeneous Nanozyme for Site‐Specific Proteolysis

The selective hydrolysis of proteins by non‐enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal‐oxo cluster [Hf₁₈O₁₀(OH)₂₆(SO₄)₁₃?(H₂O)₃₃] ( Hf₁₈ ), which is centred by the same hexamer motif found in many MOFs, acts as a heterogeneous catalyst for the efficient hydrolysis of horse heart myoglobin (HHM) in low buffer concentrations. Among 154 amino acids present in the sequence of HHM, strictly selective cleavage at only 6 solvent accessible aspartate residues was observed. Mechanistic experiments suggest that the hydrolytic activity is likely derived from the actuation of Hf^IV Lewis acidic sites and the Brønsted acidic surface of Hf₁₈ . X‐ray scattering and ESI‐MS revealed that Hf₁₈ is completely insoluble in these conditions, confirming the HHM hydrolysis is caused by a heterogeneous reaction of the solid Hf₁₈ cluster, and not from smaller, soluble Hf species that could leach into solution.     

Solid‐State Dynamics of Uranyl Polyoxometalates

Understanding fundamental uranyl polyoxometalate (POM) chemistry in solution and the solid state is the first step to defining its future role in the development of new actinide materials and separation processes that are vital to every step of the nuclear fuel cycle. Many solid‐state geometries of uranyl POMs have been described, but we are only beginning to understand their chemical behavior, which thus far includes the role of templates in their self‐assembly, and the dynamics of encapsulated species in solution. This study provides unprecedented detail into the exchange dynamics of the encapsulated species in the solid state through Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy. Although it was previously recognized that capsule‐like molybdate and uranyl POMs exchange encapsulated species when dissolved in water, analogous exchange in the solid state has not been documented, or even considered. Here, we observe the extremely high rate of transport of Li⁺ and aqua species across the uranyl shell in the solid state, a process that is affected by both temperature and pore blocking by larger species. These results highlight the untapped potential of emergent f‐block element materials and vesicle‐like POMs.     

A study of the reactivity of elemental Cr/Se/Te thin multilayers using X-ray reflectometry, in situ X-ray diffraction and X-ray absorption spectroscopy

The reactivity of [Cr/Se/Te] multilayers under annealing was investigated using X-ray reflectometry, in situ X-ray diffraction, X-ray absorption fine structure (XAFS) measurements and transmission electron microscopy. For all samples, interdiffusion was complete at temperatures between 100 and 300 °C, depending on the repeating tri-layer thickness. A crystalline phase nucleated approximately 20 °C above the temperature where interdiffusion was finished. The first crystalline phase in a binary Cr/Te sample was layered CrTe₃ nucleating at 230 °C. In ternary samples (Se:Te=0.6-1.2), the low-temperature nucleation of such a layered CrQ₃ (Q=Se, Te) phase is suppressed and instead the phase Cr₂Q₃ nucleates first. Interestingly, this phase decomposes around 500 °C into layered CrQ₃. In contrast, binary Cr/Se samples form stable amorphous alloys after interdiffusion and Cr₃Se₄ nucleates around 500 °C as the only crystalline phase. Evaluation of the XAFS data of annealed samples yield Se-Cr distances of 2.568(1) and 2.552(1) Å for Cr₂Q₃ and CrQ₃, respectively. In the latter sample, higher coordination shells around Se are seen accounting for the Se-Te contacts in the structure.     

Investigation of silver-containing layered materials and their interactions with primary amines using solid-state 109Ag and 15N NMR spectroscopy and first principles calculations

Silver-containing layered networks of the form [Ag(L)] (L = 4-pyridinesulfonate or p-toluenesulfonate) were treated with primary amines in different ratios. The structures of the parent supramolecular networks are well-known; however, their interactions with primary amines lead to the formation of new layered materials for which single-crystal X-ray structures cannot be obtained. Solid-state (109)Ag, (15)N, and (13)C cross-polarization magic-angle spinning (CP/MAS) NMR experiments, in combination with powder X-ray diffraction experiments and ab initio calculations, are utilized to investigate the interactions between the primary amines and the parent materials, and to propose structural models for the new materials. (109)Ag chemical shift (CS) tensor parameters are extremely sensitive to changes in silver environments; hence, (1)H-(109)Ag CP/MAS NMR experiments are used to distinguish and characterize silver sites. The combination of (109)Ag and (15)N NMR experiments on starting materials and samples prepared with both (15)N-labeled and unlabeled amines permits the accurate measurements of indirect (1)J((109)Ag,(15)N) and (1)J((109)Ag,(14)N) spin-spin coupling constants, providing further information on structure and bonding in these systems. First principles calculations of silver CS tensors and (1)J((109)Ag,(14)N) coupling constants in model complexes aid in formulating the proposed structural models for the new materials, which are largely comprised of layers of silver-diamine cations.     

Composition analysis of single semiconductor nanowires using pulsed-laser atom probe tomography

We report the composition analysis of single InAs and Si semiconductor nanowires using pulsed-laser atom probe tomography. The experimental conditions and sample geometries needed to realize 3-D composition mapping are described in detail. InAs mass spectra obtained using voltage pulses and laser pulses are compared, and are found to be superior for pulsed-laser evaporation. The ability to analyze intrinsic Si nanowires using pulsed laser evaporation is demonstrated. No peaks associated with the gold catalyst used were found in the InAs or the Si nanowire mass spectra. PACS 68.70.+w; 61.82.Fk; 61.72.Ss     

Emission Spectrochemical Analysis of Metals Using a Nitrogen Laser

Comparative studies of the possibilities of using pulsed nitrogen and Nd:YAG lasers for emission spectrochemical analysis of copper-zinc alloys have been made. The nitrogen laser developed on the basis of the commercial excimer laser provided an energy of radiation pulses of 5 mJ with an error of less than 0.8% at a repetition frequency of 100 Hz. The high stability and the high pulse repetition frequency of the nitrogen laser were attained due to the additional high-speed fan inside the laser chamber, which provided agitation and circulation of the gas mixture. It has been shown by experiment that the spectral emission of the plasma formed by means of the nitrogen laser is characterized by intensity fluctuations with a root-mean-square deviation of 1.4%, whereas in the case of using an Nd:YAG laser it was 14.3%. The advantages of the nitrogen laser that are due to the increased signal-to-background ratio and the suppression of the selective evaporation effect have been revealed.