C 60 and the icosahedral group Ih: Simplification methods and group-theoretical applications

Group-theoretical methods are used to induce “global” distortions of C ₆₀ from basis function(s) of a single “local” distortion in two cases: (1) The 60 vibrational modes arising from radial displacements of carbon atoms are found in terms of basis functions of A′, the one-dimensional symmetric representation of C_s; (2) The 24 vibrational modes arising from tangential displacements of hypothetical atoms placed at pentagon centers are found in terms of basis functions of E ₁, the vector irreducible representation of C_5v . The induction process is simplified by an icon notation (v) or (vμ) which uniquely labels the operations in I_h if μ,v = 0, 1, 2, 3, 4 and under/over lining of a digit is included. These icons describe the transformations IUS^vTS^μ of Felix Kline referred to a five-fold z-axis and two-fold x-axis and serve to label and “distinguish” symmetrically equivalent points of the truncated icosahedron.     

Ultra‐Narrow‐Band Blue‐Emitting Oxoberyllates AELi2[Be4O6]:Eu2+ (AE=Sr,Ba) Paving the Way to Efficient RGB pc‐LEDs

Highly efficient phosphor‐converted light‐emitting diodes (pc‐LEDs) are popular in lighting and high‐tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra‐narrow band blue emitting oxoberyllates AELi₂[Be₄O₆]:Eu²⁺ (AE=Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi₂[(Al₂Si₂)N₆]:Eu²⁺. The oxoberyllates’ extremely small Stokes shift and unprecedented ultra‐narrow band blue emission with fwhm ≈25 nm (≈1200 cm^?1) at λ_em=454–456 nm result from its rigid, highly condensed tetrahedra network. AELi₂[Be₄O₆]:Eu²⁺ allows for using short‐wavelength blue LEDs (λ_em<440 nm) for efficient excitation of the ultra‐narrow band blue phosphor, for application in violet pumped white RGB phosphor LEDs with improved color point stability, excellent color rendering, and high energy efficiency.     

Magnetoabsorption in n-type InSb from 8 to 15 μm

Magnetoabsorption measurements in n-type InSb at T?30K have been made between ～ 8 and 15 μm using magnetic fields up to 150 kOe. The observed absorption peaks are identified as due to combined resonance, harmonics of cyclotron resonance and the corresponding LO phonon-assisted resonances. These resonant absorptions are considered to be important in the interpretation of the observed magnetic field behavior of the threshold and output power of the InSb spin-flip Raman laser pumped with 10.6 μm CO₂ laser.     

Sensory principles of higher plants

Plants respond to a broad variety of stimuli from the interior of their body and from the outside environment. A revolution in our knowledge of the sensory capabilities of plants took place during the last decade, thanks to the consequent application of the tools of molecular genetics and the focusing of most work, in a world-wide effort, on a single, representative, higher plant: Arabidopsis thaliana. This review concentrates on the complete sensory periphery of higher plants, with focus placed on the principles rather than the details, and such systems that have been functionally identified unambiguously. Higher plants are no less fascinating, no less complex, and no less sensitive than animals, even man, with respect to their sensory capabilities. Plants constantly monitor their environment and their interior situation by using a stunning array of sensory systems, that are mostly different from those of animals or man.     

Der zweistufige Carbanion-Mechanismus der Fragmentierung von 3-Aminopropylbenzoaten. Fragmentierungs-Reaktionen. 25. Mitteilung

The unsubstituted and p-substituted benzoates 2b – 2e of 3-dimethylamino-2,2bis(p-nitrophenyl)-propanol ( 2a ) undergo quantitative fragmentation in 80% ethanol yielding 1,1-bis(p-nitrophenyl)-ethylene ( 5 ) besides formaldehyde and dimethylamine, the hydrolysis products of the imonium ion 3 . The corresponding alcohol 2a , however, yields 2,2-bis(p-nitrophenyl)-ethanol ( 9 ) in addition to fragmentation products. Conversely, no fragmentation is observed with the benzoates 6b – 6e of 3-dimethylamino-2,2-diphenylpropanol ( 6a ) which lack electronwithdrawing substituents in the β-phenyl groups. These results are in agreement with a two-step carbanion mechanism (Scheme 2) involving the ionization of the aminoalkohol 2a and its esters 2b – 2e to the imonium ion 3 and the carbanions 4a – 4e . The latter undergo competitive cleavage, recombination and protonation to 5 , 2 and 9 , respectively, depending on the nucleofugal activity of –X. These conclusions are supported by the first-order rate constants for the benzoates 2b – 2e which differ merely by a factor of three. Since the p-substituents in the benzoate groups have only a minor effect on the reaction rate the bonds to the nucleofugal groups are not appreciably broken in the rate determining step.     

Inverse-Tunable Red Luminescence and Electronic Properties of Nitridoberylloaluminates Sr2−xBax[BeAl3N5]:Eu2+ (x=0–2)

The nitridoberylloaluminate Ba₂[BeAl₃N₅]:Eu²⁺ and solid solutions Sr_2−xBa_x[BeAl₃N₅]:Eu²⁺ (x=0.5, 1.0, 1.5) were synthesized in a hot isostatic press (HIP) under 50 MPa N₂ atmosphere at 1200 °C. Ba₂[BeAl₃N₅]:Eu²⁺ crystallizes in triclinic space group (no. 2) (Z=2, a=6.1869(10), b=7.1736(13), c=8.0391(14) Å, α=102.754(8), β=112.032(6), γ=104.765(7)°), which was determined from single-crystal X-ray diffraction data. The lattice parameters of the solid solution series have been obtained from Rietveld refinements and show a nearly linear dependence on the atomic ratio Sr : Ba. The electronic properties and the band gaps of M₂[BeAl₃N₅] (M=Sr, Ba) have been investigated by a combination of soft X-ray spectroscopy and density functional theory (DFT) calculations. Upon irradiation with blue light (440–450 nm), the nitridoberylloaluminates exhibit intense orange to red luminescence, which can be tuned between 610 and 656 nm (fwhm=1922–2025 cm⁻¹ (72–87 nm)). In contrast to the usual trend, the substitution of the smaller Sr²⁺ by larger Ba²⁺ leads to an inverse-tunable luminescence to higher wavelengths. Low-temperature luminescence measurements have been performed to exclude anomalous emission.     

Unsaturated dodecahedranes--in quest of the C20H14 1,4,16-triene and C20H12 1,4,10(14),16-tetraene, and their cations and anions

The highly pyramidal, highly strained 1,4,16-dodecahedratriene (4) and C20H12 1,4,10(14),16-dodecahedratetraene (5) are cage olefins with an intriguing "inner life". For 5 DFT calculations give information about the energetic and geometrical consequences of one-/two-electron oxidation and reduction. Attempts to prepare 4 and 5 through thermal retro[2+2]/[4+2]cycloaddition strategies proved unsuccessful. Still, the C20H14/C20H12 cage cations and anions are liberated upon electron impact or gas-discharge ionization of their thermally extremely stable tris-/tetrakisanthraceno-anellated derivatives. Mass-selection (photoelectron (PE) characterization) of the anions failed, however, due to the very small anion intensity, the preferential formation of hydrogen-poor ions, and minor cage disruption.