Materials Literature
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The cations [Pd2Cl2L]2+ and [KL2′+ (L = [18]aneN2S4, L′ =[15]aneO5) have been used as templates for the synthesis of unique three-dimensional polyiodide networks. The metal cations in [Pd2Cl2L]1.5I5(I3)2 are linked into infinite chains by pairwise hydrogen bonding; the resulting cationic polymers run through channels…
Not threading rings on chains, but chains through rings results in a new class of main-chain polyrotaxanes. The cations of bipyridinium salts thread through the crown ether units of a poly(ester crown ether) chain (shown below). The threading efficiency m/n of the polyrotaxane is controlled by stoichiometry and temper…
The heterogenization of a titanium(IV) silsesquioxane complex in an MCM-41 molecular sieve, by tailoring the polarity of MCM-41, results in self-assembled materials (see the space-filling model on the right) that are active, truly heterogeneous, and recyclable catalysts for liquid-phase alkene epoxidation.
Two new molecular magnets, the dodecanuclear manganese complexes of the type [Mn12O12(O2CR)16(H2O)4] (known for R = CH3, new for R = o-ClC6H4, o-BrC6H4) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization…
We have identified the surface polar structure of wurtzite-type ZnO films by coaxial impact-collision ion scattering spectroscopy. High-quality ZnO epitaxial films were prepared on sapphire (α-Al2O3) (0001) substrates by laser molecular beam epitaxy using a ZnO ceramic target. The (0001̄) crystallographic plane (the O…
The ground-state energy of excitons confined in microspherical crystallites with a finite-height potential wall is studied variationally as a function of the particle radius in the so-called strong-confinement regime. Exciton energies for dot radii in the range 5-40 Å are calculated and compared with experimental and…
We report a systematic study of the electronic transport properties of the metallic perovskite oxide as a function of the oxygen stoichiometry . The electrical resistivity, magnetoresistance, susceptibility, Hall effect and thermopower have been studied. All of the transport coefficients are dependent on the value of…
Intense chiroptical properties and efficient reversibility of the chemical redox cycle support the adaptability of the CuI/CuII complex system 1/2 for the development of a binary molecular device. Reduction proceeds with ascorbic acid, and oxidation with ammonium persulfate.
Small molecules of the indene and pseudoazulene type like 1 and 2 form columnar mesophases! These compounds do not possess peripheral flexible chains like conventional columnar liquid crystals. Instead, polarizable chlorine and sulfur atoms, as well as the polar cyano group, function as unusual soft regions between th…
Frequency upconversion of cw infrared radiation at 1.06 μm into the visible in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glass samples is presented. Intense green and red emission bands around 530, 555, and 670 nm, respectively, are observed in addition to near-infrared 830 and 925 nm less intense signals. Energy tra…
We study the dynamics of a system composed of interacting units each with a complex internal structure comprising many subunits and treat the case in which each subunit grows in a multiplicative manner. We propose a model for such systems in which the interaction among the units is treated in a mean field approximatio…
A mechanical switch in a [2]catenane, made up of a cyclobis(paraquat-p-phenylene) tetracation interlocked with a macrocyclic polyether containing a redox-active tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene ring system, can be thrown either chemically or electrochemically. The neutral TTF unit resides “insi…
We have measured the energy-momentum density of amorphous silicon dioxide using an $(e,2e)$ spectrometer with 20.8 keV incident, 19.6 keV scattered, and 1.2-keV ejected electron energies. The amorphous ${\mathrm{SiO}}_{2}$ sample was prepared by oxidizing a thin silicon membrane. The experimental data show a valence e…
The results of a combined study of the temperature variation of photoluminescence (PL) and dc conductivity from high optical-quality free-standing porous silicon films are presented. PL spectra of the samples have been studied in the range 10–300 K. Dc conductivity (σ) on these samples have been studied from 90 to 300…
Molecular dynamics (MD) simulation of the diffusion of water in both atactic polypropylene (aPP) and amorphous isotactic polypropylene (iPP) models has been performed. Constant particle number, constant pressure, and constant temperature (NPT) MD was employed for both systems consisting of three polypropylene chains o…
Crystal structures of turkey egg lysozyme (TEL) and human lysozyme (HL) were refined by full-matrix least-squares method using anisotropic temperature factors. The refinement converged at the conventional R-values of 0.104 (TEL) and 0.115 (HL) for reflections with Fo > 0 to the resolution of 1.12 A and 1.15 A, respect…
We have measured the temperature and frequency dependences of large (1600--2000 ppm) shifts in the ${}^{23}\mathrm{Na}$ NMR frequencies observed for sodium atoms encapsulated in silicon cages of three clathrate compounds: ${\mathrm{Na}}_{x}@{\mathrm{Si}}_{136},$ ${\mathrm{Na}}_{x}@{\mathrm{Si}}_{46},$ and $(\mathrm{N}…
Optical absorption, Stokes, and anti-Stokes photoluminescence were performed on Er3+–Yb3+ co-doped fluoroindate glasses. For compounds prepared with a fixed 2 mol % ErF3 concentration and YbF3 contents ranging from 0 to 8 mol %, important upconversion processes were observed as a function of temperature and photon exc…
We have measured low-temperature size-selective photoluminescence excitation spectra of high-quality InP quantum dots prepared by collodial chemistry. A set of samples with mean emission energies in the range from 1.9 to 2.2 eV was investigated. All samples have a size distribution of about 10%, resulting in an inhomo…
The upconversion luminescence of a ${\mathrm{Dy}}^{3+}$-doped system is presented and analyzed. ${\mathrm{CsCdBr}}_{3}:x%$ ${\mathrm{Dy}}^{3+}$ ($x=0.2,$1,5) was synthesized and grown as crystals using the Bridgman technique. ${\mathrm{Dy}}^{3+}$ ions preferentially enter this host as charge-compensated dimers. Due to…