1,721,025 research outputs found
The effect of pressure on CD spectra of the chiral octahedral transition metal complexes Lambda-, Delta- and (Lambda, Delta)[Cr[(+)(S)(S)Mebdtp]3]
No full textThe effect of pressure on circular dichroism (CD) spectra of the octahedral chiral Lambda-, Delta- and (Lambda, Delta)tris(O,O′-bis[(+)(S)-2-methylbutyl]dithiophosphate)Cr(III) complexes, have been studied in the pressure range 0-2.5 GPa. Results on polycrystalline samples dispersed in nujol show a pressure-induced Delta to Lambda inversion of configuration at the metal center above 1.2 GPa. The high pressure stability of the Lambda-form is explained in terms of most favoured crystal packing among different ligand conformations of the chiral complex
Solid-state photodimerization of 9-methyl-anthracene
No full textRaman microscopy has been used to study the crystal-to-crystal photodimerization of 9-methyl-anthracene, analyzing the time evolution of both the molecular and the lattice phonon spectra during the transformation from the reactant to the product. This has made possible the concomitant detection of the chemical and crystal lattice changes in the same portion of the irradiated crystal. The topochemical mechanism of this reaction produces a fast process leading to a complete transformation of the monomer into the dimer. Copyright © 2016 John Wiley & Sons, Ltd
Spettroscopia Raman e polimorfismo: il ruolo dei fononi
No full textPer quanto la spettroscopia Raman sia una tecnica consolidata nello studio del polimorfismo, l'attenzione alla zona spettrale dei modi reticolari (fononi ottici) non ha ancora assunto il rilievo che merita la sua potenzialità di indagine. In questo articolo si illustra brevemente lo stato dell'arte al riguardo, con rilevanti applicazioni nel campo della tecnologia e della farmaceutica
Raman Identification of Polymorphs in Pentacene Films
No full textWe use Raman spectroscopy to characterize thin films of pentacene grown on Si/SiO x by Supersonic Molecular Beam Deposition (SuMBD). We find that films up to a thickness of about 781 Å (∼ 52 monolayers) all belong to the so-called thin-film (TF) phase. The appearance with strong intensity of some lattice phonons suggests that the films are characterized by good intra-layer order. A comparison of the Raman spectra in the lattice and CH bending spectral regions of the TF polymorph with the corresponding ones of the high-temperature (HT) and low-temperature (LT) bulk pentacene polymorphs provides a quick and nondestructive method to identify the different phases
The impact of solid solution composition on kinetics and mechanism of [2 + 2] photodimerization of cinnamic acid derivatives
Full text linkWe propose the use of solid solutions for the modulation of the kinetic in [2+2] photocycloaddition. Solid solutions with general formula [1H]BrxCl1‒x (1 = 4-amino-cinnamic acid; 0 < x < 1) were prepared via mechanochemical methods, structurally characterized, and found to undergo a single-crystal-to-single-crystal [2+2] photodimerization. The effect of the solid solutions composition on the kinetics was successfully investigated via a combination of FTIR and Principal Component Analysis (PCA), and the results were compared with those obtained for the parent materials [1H]Cl and [1H]Br. All systems follow the same nearly first-order law, and the overall reaction kinetics is influenced by a subtle interplay of structural and electronic factors as well as other processes regulating the formation and lifetime of the reacting excimer
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fast identification of rubrene polymorphs by lattice phonon Raman microscopy
No full textConfocal Raman microscopy in the lattice phonon region has been used to study the polymorphism of the organic semiconductor 5,6,11,12-tetraphenyl-tetracene (rubrene). Following literature guidelines, crystals of rubrene have been prepared using a number of solution growth and vapour deposition methods, obtaining samples of different morphologies which could be related to the various polymorphs of this compound. The technique has enabled us an easy and non invasive identification of the three known polymorphs and of their phase homogeneity with a lateral spatial resolution below 1 Î1⁄4m
Simulated Raman spectra of four tetraphenylbutadiene polymorphs
No full textWe report a combined experimental and theoretical investigation on the Raman spectra of the polymorphs α, β, γ, and δ of 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), in the region of the intramolecular modes. The interpretation of the polarized spectra is supported by ab-initio calculations for the isolated molecules and by lattice dynamics calculations for the crystals. The calculations reproduce the peculiar, and surprisingly large, differences among the spectra of the various polymorphs. The phenyl groups of 1,1,4,4-tetraphenyl-1,3-butadiene may arrange themselves around the butadiene skeleton in 2 stable conformers, which have either inversion (Ci) or 2-fold (C2) symmetry and therefore exhibit intramolecular vibrations with quite different Raman selection rules and spectra. The compound forms 4 crystalline polymorphs (α, β, γ, and δ) with different combinations of Ci and C2 conformers, and correspondingly different intramolecular spectra. The theoretical calculations provide a quantitative analysis of the various spectra
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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