Search results for "Linea"

NonclassicalPschorr andSandmeyer Reactions in Pyrazole Series

2005

The diazonium salt derived from 4-amino-N,1,3-trimethyl-N-(3-methyl-1-phenyl-1H-pyrazol-5-yl)-1H-pyrazole-5-carboxamide (14) was reacted with a mixture of CuSO4 and NaCl, with ascorbic acid as an initiator to afford the planar derivative 4,6-dihydro-1,4,6,8-tetramethyl-3-phenyldipyrazolo[3,4-b:4′,3′-d]pyridin-5(3H)-one (16) and its unexpected isomer 4,6-dihydro-3,4,6,8-tetramethyl-1-phenyldipyrazolo[4,3-b:4′,3′-d]pyridin-5(1H)-one (17), as well as the epimers (3S,4S)- (or (3S,4R)-) and (3S,4R)- (or (3S,4S)-) 4-chloro-2,4-dihydro-1′,3′,5,5′-tetramethyl-2-phenylspiro[pyrazole-3,4′(1′H)-pyrrolo[3,4-c]pyrazol]-6′(5′H)-one (18a and b, respectively). Epimers 18a and b were converted under basic c…

Conjugated Oligomers with Terminal Donor–Acceptor Substitution

2005

Conjugated oligomers represent a prominent class of compounds from a viewpoint of their theory, synthesis, and applications in materials science. Push-pull substitution with an electron donor D at one end of the conjugation and an electron acceptor A at the other end results in them having outstanding optical and electronical properties. This Review highlights fundamental synthetic strategies for the preparation of such oligomers with n repeat units (n=1, 2, 3, 4, ..) and the rules that govern their linear and nonlinear optical properties (absorption, frequency doubling and tripling). The unification of chemical, physical, and theoretical aspects with an interdisciplinary image of this clas…

Theoretical characterization of the electronic structure of polymeric systems combining disilanylene and /spl pi/-conjugated units

1994

Summary form only given. Polymeric organosilicon systems are in the forefront of research, due to their intriguing properties (semiconducting behavior, photoconduction, non-linear optical properties, and thermo- and piezochromism). The fundamental skeletons of most of these polymers consist of a /spl sigma/-electron network formed by silicon-silicon bonds. Recently, polymeric organosilicon systems containing a regular alternation of a disilanylene unit and carbon /spl pi/-conjugated moiety as phenylene, ethynylene, or ethenylene have been synthesized. The purpose of this contribution is to perform a detailed study of the electronic structure of polymers containing alternated disilanylene an…

Investigation on the indentation behavior of sandwich beams using crushable and hyperelastic foam cores

2010

In this work the indentation behaviour of sandwich beams is studied adopting the classical approach representing the core material as a Winkler-type foundation. It is shown how most of the proposed theories can be derived from a general fourth order linear differential equation expressing the equilibrium of the indented beam skin. Different assumptions on the supporting boundary constraints and materials constitutive behaviour, lead to simplifications of the general equation and to the prediction of different indentation features. An extension of the Segment-Wise approach recently proposed in the literature is in particular presented with potential to better simulate foam cores with markedl…

Relationship between Metabolic Fluxes and Sequence-Derived Properties of Enzymes

2014

Metabolic fluxes are key parameters of metabolic pathways being closely related to the kinetic properties of enzymes, thereby could be dependent on. This study examines possible relationships between the metabolic fluxes and the physical-chemical/structural features of enzymes from the yeast Saccharomyces cerevisiae glycolysis pathway. Metabolic fluxes were quantified by the COPASI tool using the kinetic models of Hynne and Teusink at varied concentrations of external glucose. The enzyme sequences were taken from the UniProtKB and the average amino acid (AA) properties were computed using the set of Georgiev’s uncorrelated scales that satisfy the VARIMAX criterion and specific AA indices th…

Non-linear optical spectra of excitons in polydiacetylene

1992

Abstract Adding long-range Coulomb interactions to the Su-Schrieffer-Heeger model makes it possible to investigate excitonic states in conjugated polymers. Various characteristic features due to these states as well as due to the electron-hole continuum can be found in the calculated non-linear optical susceptibilities. In particular the electroabsorption spectrum and the third harmonic generation intensity and its dependence on the system size are examined. Using only moderate interaction strength, various experiments in polydiacetylene can be interpreted in a consistent way.

Stability of the functional NLO polymers–optically induced depoling of the DMABI molecules in sPMMA matrix

2008

Abstract Low polar order (PO) stability is the major problem of the polymer materials for nonlinear optical (NLO) applications. In this contribution we will show the results of PO stability investigations in the corona poled 3 wt.% DMABI + sPMMA guest–host system. Influence of the poling temperature on the building and stability of the polar order in the system will be presented. To characterize the stability, PO destruction has been caused by high intensity light. Polar order stability characteristics were obtained from the sample second harmonic generation intensity (SHI) time decays. We have found that the decay signal is the best fit to the sum of two exponentials. Several physical mode…

<title>All-optical poling of DMABI molecules in a polymer matrix</title>

2005

Many organic compounds in solid state have nonlinear optical properties due to the orientation of the molecules in a polymer matrix. In this work, all-optical poling and second harmonic generation in a composition consisting of 1 mass% of N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) compound in poly(methyl methacrylate) (PMMA) matrix were studied. Thin films were prepared by solvent casting. The 1.064-μm fundamental and 532-nm second harmonic wavelengths of a Nd:YAG laser were used. It is shown that DMABI molecules can be oriented by the method of all- optical poling, and that the process is related to the photoinduced switching between two equally stable states of the molecule.

TI: Cyclophosphazenes as polymer modifiers

2003

The utilization of cyclophosphazenes as polymer modifiers is reviewed, with particular concern to their exploitation as versatile chain extenders, possibly for recycle problems, crosslinkers, to enhance mechanical properties of polymeric materials, branchers, to selectively introduce ramifications in linear polymers, and compatibilizers, to favor the formation of blends between originally incompatible organic macromolecules. The great versatility of the synthetic methods put forward for these substrates, together with the ease of controlling their modification, functionalization and reactivity are important parameters for the evaluation of which type of use is more feasible for these trimer…

1976

Polyoctenylenes and polydodecenylenes prepared by the methathesis reaction exhibit a bimodal molecular weight distribution. The low molecular weight fraction consists of cyclic oligomers, the high molecular weight fraction is assumed to contain linear polymers. The distribution of cyclic oligomers together with the polymer material indicates a ring-chain equilibrium. The slope of the plot log Kx (molar cyclization equilibrium constant) vs. log x (degree of polymerization) is close to −2,5 as predicted by the Jacobson and Stockmayer theory for unstrained macrocycles. Polyoctenylene und Polydodecenylene, dargestellt mit Hilfe der Metathese-Reaktion, weisen eine bimodale Molekulargewichtsverte…