Remarkable luminescence properties of lanthanide complexes with asymmetric dodecahedron structures

The distorted coordination structures and luminescence properties of novel lanthanide complexes with oxo‐linked bidentate phosphane oxide ligands—4,5‐bis(diphenylphosphoryl)‐9,9‐dimethylxanthene (xantpo), 4,5‐bis(di‐tert‐butylphosphoryl)‐9,9‐dimethylxanthene (tBu‐xantpo), and bis[(2‐diphenylphosphoryl)phenyl] ether (dpepo)—and low‐vibrational frequency hexafluoroacetylacetonato (hfa) ligands are reported. The lanthanide complexes exhibit characteristic square antiprism and trigonal dodecahedron structures with eight‐coordinated oxygen atoms. The luminescence properties of these complexes are characterized by their emission quantum yields, emission lifetimes, and their radiative and nonradiative rate constants. Lanthanide complexes with dodecahedron structures offer markedly high emission quantum yields (Eu: 55–72 %, Sm: 2.4–5.0 % in [D₆]acetone) due to enhancement of the electric dipole transition and suppression of vibrational relaxation. These remarkable luminescence properties are elucidated in terms of their distorted coordination structures.     

Regulation of folding and photochromic reactivity of terarylenes through a host-guest interaction

The photochromic reactivity of terarylenes is integrated with molecular folding that is controlled through a host-guest interaction. A thieno[3,2,b]pyridine unit is introduced into a photochromic terarylene structure as an aryl unit to form a guest-interacting site. Thienopyridine-containing terarylenes showed solvent-dependent photochromic reactivity in solution. A terarylene moiety that contains two thienopyridyl units showed significantly high photocoloration reactivity as high as 88% of photocyclization quantum yield in methanol, whereas that value was only 24% in hexane. A temperature-dependent (1)H NMR spectroscopic study in different solvents indicated an interconversion between photochromic-reactive and unreactive conformations. In methanol, the intermolecular interaction between terarylene species and the solvent molecule slows the rate of interconversion and increases the population of the photochromic-active form, whereas the unreactive conformation is dominant in hexane. Crystal-structural studies demonstrated the perfect regulation of molecular folding between a photochromic-active form and an unreactive conformation by changing the solvents for recrystallization. Single crystals prepared from solutions in methanol showed reversible photochromic reactivity, whereas recrystallization from solutions in hexane did not show this reactivity. X-ray crystallographic studies of single crystals from solutions in methanol demonstrated that the photochromic molecules bind a solvent methanol molecule at the guest-interacting site to regulate the molecular conformation into a photochromic-active form in collaboration with specific intramolecular interactions, whereas crystals from solutions in hexane possess the photochromic-unreactive conformation.     

Ion-pairing π-electronic systems: ordered arrangement and noncovalent interactions of negatively charged porphyrins

In this study, charged π-electronic species are observed to develop stacking structures based on electrostatic and dispersion forces. ⁱπ–ⁱπ Interaction, defined herein, functions for the stacking structures consisting of charged π-electronic species and is in contrast to conventional π–π interaction, which mainly exhibits dispersion force, for electronically neutral π-electronic species. Establishing the concept of ⁱπ–ⁱπ interaction requires the evaluation of interionic interactions for π-electronic ion pairs. Free base (metal-free) and diamagnetic metal complexes of 5-hydroxy-10,15,20-tris(pentafluorophenyl)porphyrin were synthesized, producing π-electronic anions upon the deprotonation of the hydroxy unit. Coexisting cations in the ion pairs with porphyrin anions were introduced as the counter species of the hydroxy anion as a base for commercially available cations and as ion-exchanged species, via Na⁺ in the intermediate ion pairs, for synthesized π-electronic cations. Solid-state ion-pairing assemblies were constructed for the porphyrin anions in combination with aliphatic tetrabutylammonium (TBA⁺) and π-electronic 4,8,12-tripropyl-4,8,12-triazatriangulenium (TATA⁺) cations. The ordered arrangements of charged species, with the contributions of the charge-by-charge and charge-segregated modes, were observed according to the constituent charged building units. The energy decomposition analysis (EDA) of single-crystal packing structures revealed that electrostatic and dispersion forces are important factors in stabilizing the stacking of π-electronic ions. Furthermore, crystal-state absorption spectra of the ion pairs were correlated with the assembling modes. Transient absorption spectroscopy of the single crystals revealed the occurrence of photoinduced electron transfer from the π-electronic anion in the charge-segregated mode.

π-Electronic ion pairs comprising porphyrin-based π-electronic anions have exhibited characteristic assembling modes and resulting electronic properties such as solid-state absorption and photoinduced electron transfer.     

Density measurements of non-crystalline materials under high pressure and high temperature

Abstract

We have developed a new method for density measurements by means of X-ray absorption under high pressure and high temperature using a multi-anvil apparatus combined with a synchrotron-radiation source. To overcome the effect of the variation of the sample thickness under pressure, a sapphire ball was put in the sample capsule as a calibrant of the thickness, and the intensity of the transmitted X-ray beam was measured as a function of the sample position. The densities of crystalline and liquid tellurium were measured up to 5 GPa and up to 700°C. Discontinuous changes in the density at the Te I-Te 11 transition and at the melting were clearly observed.     

The dynamic Casimir effect within a vibrating metal photonic crystal

The lattice-vibrating metal photonic crystal is exactly a system of dynamical Casimir effect connected in series, and so we can expect that a dynamical Casimir effect is enhanced by the photonic band effect. In the present study, when an electromagnetic field between metal plates is in the ground state in a one-dimensional metal photonic crystal, the radiation of electromagnetic wave in excited states has been investigated by artificially introducing lattice vibration to the photonic crystal. In this case as well as a dynamical Casimir effect, it has been shown that the harmonics of a ground state are generated just by vibrating a photonic crystal even without an incident wave. The dependencies of the radiating power on the number of layers and on the wavenumber of the lattice vibration are remarkable. It has been found that the radiation amplitude on lower excited states is not necessarily large and radiation on specific excited levels is large.     

Level set-based topology optimization for anti-reflection surface

We present a level set-based topology optimization method to model anti-reflection surfaces (ARSs). An objective functional is defined as an integration of scattering intensity of an electric field, and the ARSs are optimally designed by minimizing reflections at the air-dielectric interface. During the topology optimization, geometric constraints are controlled by adjusting a regularization parameter. The performance of the ARSs improves as the value of the regularization parameter becomes small. Level set functions are used to express dielectric structures, and dielectric boundaries are interpreted as lines on the iso-surface of the level set functions.     

C^*-Algebras Associated with Complex Dynamical Systems and Backward Orbit Structure

Let $R$ be a rational function. The iterations $(R^n)_n$ of $R$ gives a complex dynamical system on the Riemann sphere. We associate a $C^*$ -algebra and study a relation between the $C^*$ -algebra and the original complex dynamical system. In this short note, we recover the number of $n$ th backward orbits counted without multiplicity starting at branched points in terms of associated $C^*$ -algebras with gauge actions. In particular, we can partially imagine how a branched point is moved to another branched point under the iteration of $R$ . We use KMS states and a Perron–Frobenius type operator on the space of traces to show it.     

Spin-polarization of radioactive 123Ing.s. by the tilted-foil method

A spin-polarized radioactive ¹²³In (I ^π , g = 1.220(2) , T _1/2 = 5.97(5) s) beam has been successfully generated by the tilted-foil method. This nuclide is the heaviest ever polarized in its ground state by this method. Using the ISOL-based re-acceleration-type facility TRIAC, an ¹²³In_g.s. beam of 305 keV/nucleon went through a stack of 15 carbon foils with a tilt angle of 70^° , and an asymmetry of 0.76 ± 0.25% of β-decays was observed by the β-NMR technique. The asymmetry shows that the tilted-foil method combined with a re-acceleration facility is useful for producing spin-polarized beams for applications such as nuclear physics and materials science.     

Electrospun Cu-Deposited Flexible Fibers as an Efficient Oxygen Evolution Reaction Electrocatalyst

Developing oxygen evolution reaction (OER) catalysts with high activity, long-term durability, and at low cost remains a great challenge. Herein, we report the high activity of fibrous Cu-based catalysts. The synthesis process is simple and scalable. Electrospinning method was selected to synthesize fibrous polymer substrates (Poly(vinylidene fluoride-co-hexafluoropropylene, PVdF-HFP), which are then covered by Cu via electroless deposition. Cu-deposited PVdF-HFP with different microstructures having smooth and roughened surfaces were also synthesized by drop-casting and impregnation method, respectively, to emphasize the importance of the microstructures on OER activity. The OER activity and durability were studied by linear sweep voltammetry, chronoamperometry, and Tafel slope analysis. The Cu/PVdF-HFP fibrous catalysts exhibit significantly improved OER activity and durability compared with Cu plate as well as Cu-deposited PVdF-HFP with different microstructures. The unique fibrous structure provides better mass transport, diffusion, and large active surface area. In addition to the advantages of the fibrous structure, attenuated total reflection infrared (ATR-IR) and ex situ X-ray photoelectron spectroscopy revealed that the improved specific activity for Cu/PVdF-HFP fiber can be attributed to the synergistic effect between Cu and Cu/PVdF-HFP (electron transfer from Cu to PVdF-HFP) at the Cu|PVdF-HFP interface, which results in optimized reaction energetics for the OER.     

Tridentate Thiolate Ligands: Application to the Synthesis of the Site-Differentiated [4Fe-4S] Cluster having a Hydrosulfide Ligand at the Unique Iron Center

We have designed new trithiols Temp(SH)₃ and Tefp(SH)₃ that can be synthesized conveniently in short steps and are useful for preparation of crystalline [3:1] site-differentiated [4Fe-4S] clusters suitable for X-ray structural analysis. The ethanethiolate clusters (PPh₄)₂[Fe₄S₄(SEt)(TempS₃)] ( 4a ) and (PPh₄)₂[Fe₄S₄(SEt)(TefpS₃)] ( 4b ) were prepared as precursors, and the unique iron sites were then selectively substituted. Upon reaction with H₂S, (PPh₄)₂[Fe₄S₄(SH)(TempS₃)] ( 6a ) and (PPh₄)₂[Fe₄S₄(SH)(TefpS₃)] ( 6b ), which model the [4Fe-4S] cluster in the β subunit of (R)-2-hydroxyisocaproyl-CoA dehydratase, were synthesized. Clusters 6a and 6b were further converted to the sulfido-bridged double cubanes (PPh₄)₄[{Fe₄S₄(TempS₃)}₂(μ²-S)] ( 6b ) and (PPh₄)₄[{Fe₄S₄(TefpS₃)}₂(μ²-S)] ( 7b ), respectively, via intermolecular condensation with the release of H₂S. Conversely, addition of H₂S to 7a , 7b afforded the hydrosulfide clusters 6a , 6b . The molecular structures of the clusters reported herein were elucidated by X-ray crystallographic analysis. Their redox properties were investigated by cyclic voltammetry.