New Features in EXPO2007, a Program for Crystal Structure Resolution from Powder Data

New approaches have been introduced in the EXPO2007 program aiming at making easier and straightforward the ab initio crystal structure solution from powder diffraction data. Improvements in space group determination, powder pattern decomposition, least squares Fourier recycling, interpretation of the electron density map have been developed. To manage organic crystal structures a new strategy in direct-space, combining Direct Methods and Simulated Annealing approaches, has been implemented

New frontiers in powder diffraction pattern indexing: the program<i>N-TREOR09</i>

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Engineering Dion-Jacobson Perovskites in Polariton Waveguides

Hybrid two-dimensional perovskites hold considerable promise as semiconductors for a wide range of optoelectronic applications. Many efforts are addressed to exploit the potential of these materials by tailoring their characteristics. In this work, the optical properties and electronic band structure in three new Dion-Jacobson (DJ) perovskites (PVKs) are engineered by modulating their structural distortion. Two different interlayer cations: 1-6, Hexamethylendiammonium, HE, and 3-(Dimethylamino)-1-propylammonium, DMPA, have been selected to investigate the role of the cation length and the ammonium binding group on the crystalline structure. This study provides new insights into the understanding of the structure-property relationship in DJ perovskites and demonstrates that exciton characteristics can be easily modulated with the judicious design of the organic cations. DJ PVKs developed in this work were also grown as size-controlled single crystal microwires through a microfluidic-assisted synthesis technique and integrated in a nanophotonic device. The DJ PVK microwire acts as a waveguide exhibiting strong light-matter coupling between the crystal optical modes and DJ PVK exciton. Through the investigation of these polariton waveguides, the nature of the double peak emission, which is often observed in these materials and whose nature is largely debated in the literature, is demonstrated originating from the hybrid polariton state

New [1]benzothieno[3,2- b]benzothiophene-tetraoxide-based TADF emitters with a D–A–D structure for OLED applications

Luminescent organic molecules showing thermally activated delayed fluorescence (TADF) are appealing materials for high-efficiency OLEDs. Here, we report a new class of organic luminescent materials with TADF properties, and a D–A–D electronic structure based on [1]benzothieno[3,2-b]benzothiophene-tetraoxide BTBTOx4 as the acceptor unit A. Three donor units D were selected and coupled with BTBTOx4, using a straightforward synthetic protocol based on microwave-assisted Buchwald–Hartwig cross-coupling, to yield three organic luminescent molecules labelled PTz2-BTBTOx4, MPA2-BTBTOx4 and POCz2-BTBTOx4. Chemico-physical and structural properties were investigated by cyclic voltammetry, electrical measurements, crystallographic analysis, theoretical study and photophysical characterization. All three emitters showed high electrochemical stability with reversible oxidation waves. MPA2-BTBTOx4 was selected as the reference molecule for X-ray analysis, which revealed torsion angles of −59° and 86° between the donor (MPA) and acceptor (BTBTOx4) units supporting their appropriate structural configuration to have TADF properties. Photophysical studies highlighted a noteworthy increase in PL efficiency upon deoxygenation for all three compounds. The oxygen-induced quenching of delayed fluorescence and time-resolved photoluminescence studies supported the presence of the TADF properties, further corroborated for PTz2-BTBTOx4 and MPA2-BTBTOx4 by DFT studies. Preliminary steady-state photophysical studies were also carried out on neat films of all three emitters, revealing a pronounced self-quenching of photoluminescence for PTz2-BTBTOx4 and MPA2-BTBTOx4 and a minimal self-quenching for POCz2-BTBTOx4, which maintains a high ΦPL (22%) comparable to that in Zeonex and half of that in PMMA. As a proof of concept, the three emitting molecules were tested as neat films in simple-structure OLED devices. In accordance with the photoluminescence data, POCz2-BTBTOx4, thanks to its sterically bulky structure, retains a good emission capacity even in a neat film and was also selected as an active matrix to build OLED devices by using two different deposition techniques: inkjet-printing and spin coating

<i>Ab initio</i>structure determination by powders: recent developments in<i>EXPO2010</i>

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The Rietveld Refinement in the EXPO Software: A Powerful Tool at the End of the Elaborate Crystal Structure Solution Pathway

The Rietveld method is the most reliable and powerful tool for refining crystal structure when powder diffraction data are available. It requires that the structure model to be adjusted is as close as possible to the true structure. The Rietveld method usually represents the final step of the powder solution process, in particular when a new structure is going to be determined and published. EXPO is a software able to execute all the steps of the solution process in a mostly automatic way, by starting from the chemical formula and the experimental diffraction pattern, passing through computational methods for locating the structure model and optimizing it, and ending to the Rietveld refinement. In this contribution, we present the most recent solution strategies in EXPO, both in reciprocal and direct space, aiming at obtaining models suitable to be refined by the Rietveld method. Examples of Rietveld refinements are described, whose results are related to different solution procedures and types of compounds (organic and inorganic)

Revealing the lifelong bio-persistent crystal structure of an asbestos fibre

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Crystallographic study of PET radiotracers in clinical evaluation for early diagnosis of Alzheimers

The title compound, C24H25NO3·2CH3OH, which crystallized as a methanol disolvate, has applications as a PET radiotracer in the early diagnosis of Alzheimer's disease. The dihedral angle between the biphenyl rings is 8.2 (2)° and the heterocyclic ring adopts a half-chair conformation with the N atom adopting a pyramidal geometry (bond-angle sum = 327.6°). The C atoms of both methoxy groups lie close to the plane of their attached ring [deviations = 0.107 (6) and 0.031 (6) Å]. In the crystal, the components are linked by O—H...O and O—H...N hydrogen bonds, generating [010] chains. C—H...O interactions are also observed

New carbazole-substituted imine structures: synthesis and XRD analysis

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