Optical transitions in a vanishing conduction-band-offset superlattice

Optical transitions in the strained superlattice ZnSe/ZnS (001) have been calculated within an empirical tight-binding model followed by an appropriate evaluation of the momentum matrix elements. Vanishing conduction-band-offset has been previously established for this system, which can be considered as a realistic candidate for obtaining an “effective-mass” superlattice. Oscillator strengths, calculated for different superlattice periods, show that the usual δn=0 selection rule breaks down.     

Synthesis of novel 5-amino-1-aroylpyrazoles

A series of 5-amino-1-aroylpyrazoles 3 are synthesized directly by the reaction of β-aminocrotononitrile 1 with some structures containing the hydrazine moiety (X-NHNH₂) 2 by refluxing ethanol in presence of sodium acetate. When semicarbazide 3i was used (X = CONH₂), the reaction afforded the unexpected 7-aminopyrazolo[1,5-a]pyrimidine 4.     

Stereocontrolled alkylative construction of quaternary carbon centers

Protocols for the stereodefined formation of alpha,alpha-disubstituted enolates of pseudoephedrine amides are presented followed by the implementation of these in diastereoselective alkylation reactions. Direct alkylation of alpha,alpha-disubstituted pseudoephedrine amide substrates is demonstrated to be both efficient and diastereoselective across a range of substrates, as exemplified by alkylation of the diastereomeric pseudoephedrine alpha-methylbutyramides, where both substrates are found to undergo stereospecific replacement of the alpha-C-H bond with alpha-C-alkyl, with retention of stereochemistry. This is shown to arise by sequential stereospecific enolization and alkylation reactions, with the alkyl halide attacking a common pi-face of the E- and Z-enolates, proposed to be opposite the pseudoephedrine alkoxide side chain. Pseudoephedrine alpha-phenylbutyramides are found to undergo highly stereoselective but not stereospecific alpha-alkylation reactions, which evidence suggests is due to facile enolate isomerization. Also, we show that alpha,alpha-disubstituted pseudoephedrine amide enolates can be generated in a highly stereocontrolled fashion by conjugate addition of an alkyllithium reagent to the s-cis-conformer of an alpha-alkyl-alpha,beta-unsaturated pseudoephedrine amide, providing alpha,alpha-disubstituted enolate substrates that undergo alkylation in the same sense as those formed by direct deprotonation. Methods are presented to transform the alpha-quaternary pseudoephedrine amide products into optically active carboxylic acids, ketones, primary alcohols, and aldehydes.     

Conductive sub-micrometric wires of platinum-carbonyl clusters fabricated by soft-lithography

Conductive wires of sub-micrometer width made from platinum-carbonyl clusters have been fabricated by solution-infilling of microchannels as in microinject molding in capillaries (MIMIC). The process is driven by the liquid surface tension within the micrometric channels followed by the precipitation of the solute. Orientation of supramolecular crystalline domains is imparted by the solution confinement combined with unidirectional flow. The wires exhibit ohmic conductivity with a value of 0.2 S/cm that increases, after thermal decomposition of the platinum-carbonyl cluster precursor to Pt, to 35 S/cm.     

Four N7‐alkoxybenzyl‐substituted 4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐diones: hydrogen‐bonded supramolecular structures in zero,one, two or three dimensions

3‐tert‐Butyl‐7‐(4‐methoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₇N₃O₃, (I), 3‐tert‐butyl‐7‐(2,3‐dimethoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₂H₃₉N₃O₄, (II), 3‐tert‐butyl‐4′,4′‐dimethyl‐7‐(3,4‐methylenedioxybenzyl)‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₅N₃O₄, (III), and 3‐tert‐butyl‐4′,4′‐dimethyl‐1‐phenyl‐7‐(3,4,5‐trimethoxybenzyl)‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione ethanol 0.67‐solvate, C₃₃H₄₁N₃O₅·0.67C₂H₆O, (IV), all contain reduced pyridine rings having half‐chair conformations. The molecules of (I) and (II) are linked into centrosymmetric dimers and simple chains, respectively, by C—H...O hydrogen bonds, augmented only in (I) by a C—H...π hydrogen bond. The molecules of (III) are linked by a combination of C—H...O and C—H...π hydrogen bonds into a chain of edge‐fused centrosymmetric rings, further linked by weak hydrogen bonds into supramolecular arrays in two or three dimensions. The heterocyclic molecules in (IV) are linked by two independent C—H...O hydrogen bonds into sheets, from which the partial‐occupancy ethanol molecules are pendent. The significance of this study lies in its finding of a very wide range of supramolecular aggregation modes dependent on rather modest changes in the peripheral substituents remote from the main hydrogen‐bond acceptor sites.     

Toward crystalline molecular rotors with linearly conjugated diethynyl-phenylene rotators and pentiptycene stators

A strategy for the construction of crystalline molecular rotors involves the assemblage of chemical structures that emulate the elements of macroscopic rotary devices, such as those found in macroscopic gyroscopes and compasses. In this report, we describe an efficient and short synthetic route for preparation of molecular rotors with two pentiptycene-units linked at their central benzene ring by triple bonds to a linearly conjugated phenylene rotator. Five analogous compounds with phenol, alkoxy, or alkoxycarbonyl substituents were synthesized and fully characterized in solution and in the solid-state through various methods, such as cross-polarization magic angle spinning (CPMAS) (13)C NMR and single crystal X-ray diffraction. Molecular and packing structures obtained from single crystal X-ray diffraction and crystallization properties were analyzed with the goal of identifying the key parameters that may hinder or facilitate the formation of dynamically functional, crystalline molecular rotors.     

Exploring the Cu‐In‐S System under Solvothermal Conditions near the Composition CuIn5S8

Solvothermal syntheses of copper‐indium‐sulfides performed with different Cu:In:S ratios afforded crystallization of nanocrystalline Cu‐In‐S phases with compositions close to CuInS₂, CuIn₃S₅, and CuIn₇S₁₁. Each sample shows a different and distinguishable morphology. The minority component CuInS₂ with wurtzite‐type structure crystallizes as thin plates, which are preferably stacked parallel to black stacks. The component with composition CuIn₃S₅ forms isolated few nm thin layers being arranged like the petals of a flower growing from a common point. Finally, red CuIn₇S₁₁ is obtained as nanobelts with individual diameters of about 20 nm and lengths up to more than 1 μm. According to electron diffraction patterns and X‐ray diffractometry the structures of CuIn₃S₅ and CuIn₇S₁₁ cannot be assigned to known bulk phases of the Cu‐In‐S system, however first structure models are proposed.     

Synthesis,Characterization and X-ray Crystal Structure of the Di-Mannich Base 2,2′-(3aR,7aR/3aS,7aS)-Hexahydro-1<Emphasis Type="Italic">H</Emphasis>-benzo[<Emphasis Type="Italic">d</Emphasis>]imidazole-1,3(2<Emphasis Type="Italic">H</Emphasis>)-diyl)bis(methylene)bis(4-methylphenol)

Abstract  

The crystal structure of new racemic di-Mannich base 2,2′-(3aR,7aR/3aS,7aS)-hexahydro-1H-benzo[d]imidazole-1,3(2H)-diyl)bis(methylene)bis(4-methylphenol) (4), is reported. The structure of the title compound, C₂₃H₃₀N₂O₂, shows two intramolecular O–H···N hydrogen bonding interactions. This compound crystallizes in triclinic symmetry, in space group P−1, with lattice constants: a = 6.2563(3) ?, b = 12.1743(7) ?, c = 14.7257(7) ?, α = 108.11(1)°, β = 99.77(1)°, γ = 98.78(1), V = 1024.97(9) ?³, Z = 2, F(000) = 396, R ₁  = 8.3%, wR ₂  = 14.7%.     

Precision steering of an optical trap by electro-optic deflection

We designed, constructed, and tested a single-beam optical trapping instrument employing twin electro-optic deflectors (EODs) to steer the trap in the specimen plane. Compared with traditional instruments based on acousto-optic deflectors (AODs), EOD-based traps offer a significant improvement in light throughput and a reduction in deflection-angle (pointing) errors. These attributes impart improved force and position resolution, making EOD-based traps a promising alternative for high-precision nanomechanical measurements of biomaterials.     

(E)‐3‐{4‐[(7‐Chloroquinolin‐4‐yl)oxy]‐3‐methoxyphenyl}‐1‐(4‐methylphenyl)prop‐2‐en‐1‐one: a ladder‐like structure resulting solely from π–π stacking interactions

In the title compound, C₂₆H₂₀ClNO₃, the quinoline fragment is nearly orthogonal to the adjacent aryl ring, while the rest of the molecular skeleton is close to being planar. The crystal structure contains no hydrogen bonds of any sort, but there are two π–π stacking interactions present. One, involving the quinoline ring, links molecules related by inversion, while the other, involving the two nonfused aryl rings, links molecules related by translation, so together forming a ladder‐type arrangement