Search results for "Optica"
showing 10 items of 7696 documents
Surface periodic poling in congruent lithium tantalate
2006
The first demonstration of surface periodic poling of lithium tantalate at high voltages is reported. Periodic domain inversion with mark-to-space ratios close to the optimum 50:50 was successfully achieved down to micrometre periods with good uniformity and repeatability.
On lead-scandium tantalate solid solutions with high electrocaloric effect
1992
Abstract The PbSc0,5Ta0,5O3 solutions are found to be a useful material for active elements of microcryogenic devices based on electrocaloric effect. A temperature difference of ΔT = 1. 0-1.8 K at field intensities 20–30 kV/cm in the interval of 210–310 K can be achieved by simultaneous or separate introducing of Sb and Co ions in B-sites of the lattice. The most important contribution to the electrocaloric effect is due to field-induced Fn3m → R3m phase transition in the case of high ordering of B-ions in the perovskite structure ABO3.
ChemInform Abstract: Diaryldistyrylpyrazines: Solvatochromic and Acidochromic Fluorophores.
2014
Diaryldimethylpyrazines are the starting materials for the synthesis of C2-symmetric donor- or acceptor-substituted distyrylpyrazines. The optical properties of these cruciform-shaped dyes are dominated by the distyrylpyrazine units; the photophysics is controlled by the styryl substitution, the diaryl substituents on the central pyrazine only having a small effect. Protonation occurs on the pyrazine and/or lateral amines or azines, thereby altering the absorption and emission properties. Hypso- and bathochromism as well as fluorescence quenching depend on the nature of the terminal substituent. This, and a significant positive solvatochromism of the fluorescence, allow optical sensing of t…
1,2-Asymmetric Induction in Diastereoselective Zwitterionic Aza-Claisen Rearrangements: Key Steps in Optically Active Alkaloid Synthesis
2013
The zwitterionic aza-Claisen rearrangement of optically active N-allylpyrrolidines and α-phenoxyacetyl fluorides proceeds with complete simple diastereoselectivity (internal asymmetric induction) and complete 1,2-asymmetric induction to generate a new C–C bond adjacent to a chiral C-N-Boc functionality. The resulting γ,δ-unsaturated amides were cyclised to give the corresponding pyrrolizidinones, which enabled the determination of the relative configuration of the stereotriads. Vinyl group degradation and a final lactam reduction gave an optically active analogue of (+)-petasinine (a pyrrolizidine alkaloid). Furthermore, the stereotriad-containing amides should be useful key intermediates f…
Synthesis of chemisorbed imidazolium and phosphonium cations by reaction of ionic liquid precursors with silica.
2010
The reaction of four different basic ionic liquid precursors with Aerosil®300 is presented. Chemisorbed imidazolium and phosphonium cations, with silanolate anions as part of the silicatic support, were obtained and investigated with various solid state NMR techniques.
ChemInform Abstract: A New Tandem Cross Metathesis-Intramolecular Aza-Michael Reaction for the Synthesis of α,α-Difluorinated Lactams.
2012
Difluorinated amides are treated with methyl vinyl ketone or analogous esters to produce the desired γ- and δ-lactam units including optically active versions.
Kinetische Racematspaltungen ausgehend vonrac-Alkoholen oderrac-Carbonsäurehalogeniden unter Mitwirkung optisch aktiver Induktorbasen
1989
Bei der Umsetzung eines Molaquivalents achiraler Carbonsaurehalogenide mit zwei Molaquivalenten rac-Alkoholen entstehen unter Mitwirkung von einem Molaquivalent einer optisch aktiven Induktorbase (tertiares Amin) partiell optisch aktive Ester sowie partiell optisch aktive Alkohole in zum Teil hoher optischer Reinheit (60 – 70%). Der im Ester gebundene Anteil an Alkohol sowie der nicht umgesetzte Alkohol haben entgegengesetzte Konfiguration. Der Induktionsgrad ist ahnlich hoch, wenn man zwei Molaquivalente eines rac-Carbonsaurehalogenids mit je einem Molaquivalent eines achiralen Alkohols und einer Induktorbase umsetzt. Der Carbonsaureanteil im Ester und die freie Saure haben entgegengesetzt…
An efficient entry to optically active anti- and syn-beta-amino-alpha-trifluoromethyl alcohols.
2008
The reaction of chiral 5,6-dihydro-2H-1,4-oxazin-2-ones with TMSCF3 in the presence of a suitable activator leads to trifluoromethyl lactols, which can be selectively reduced to anti-beta-amino-alpha-trifluoromethyl alcohols. The corresponding syn diastereoisomers are obtained when the starting imines are reduced and the nitrogen atom is conveniently protected. In addition, a novel rearrangement of the CF3 group in the lactol intermediates has been observed. This represents a formal CF3 addition to the imine function in the starting substrates.
Studien zum Vorgang der Wasserstoffübertragung, 41. Elektroreduktion von Acetophenon unter Mitwirkung optisch aktiver Leitsalze
1977
Die Anderung des Carbinol/Pinakol-Verhaltnisses2) (C/P) und der optischen Induktion bei der Elektroreduktion von Acetophenon mit (1 R, 2S)-N-(3-Cyanpropyl)-N-methylephedriniumbromid (1) und (1 R, 2 S)-N,N-Dimethylephedriniumbromid (2) als Leitsalze wird untersucht in Abhangigkeit: a) vom Potential (Tabelle 1), b) von der Stromdichte (Tabelle 2), c) von Pulsbedingungen (Tabelle 3), d) vom pH (Tabelle 4), e) von der Anwesenheit anderer Kationen (Tabelle 5), f) vom Losungsmittel (Tabelle 6), g) von der Temperatur (Tabelle 7) und h) von der Art des Elektrodenmaterials (Tabelle 8). — Es werden tensammetrische und cyclovoltammetrische Messungen durchgefuhrt. Die in trockenem Dimethylformamid erha…
Recognition and sensing of fluoride anion.
2009
Fluoride anion recognition is attracting a mounting interest in the scientific community due to its duplicitous nature. It is a useful chemical for many industrial applications, and it has been used in human diet, but, recently it has been accused for several human pathologies. Here we describe the ample panorama of different approaches the chemists world-wide have employed to face the challenge of fluoride binding, and we outline some of the research which in our view can contribute to the development of this field, especially when fluoride binding has to be achieved in highly competitive protic solvents and water.