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Intermolecular Distances (intermolecular + distance)
Selected AbstractsWhite Electroluminescence by Supramolecular Control of Energy Transfer in Blends of Organic-Soluble Encapsulated PolyfluorenesADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Sergio Brovelli Abstract Here, it is demonstrated that energy transfer in a blend of semiconducting polymers can be strongly reduced by non-covalent encapsulation of one constituent, ensured by threading of the conjugated strands into functionalized cyclodextrins. Such macrocycles control the minimum intermolecular distance of chromophores with similar alignment, at the nanoscale, and therefore the relevant energy transfer rates, thus enabling fabrication of white-light-emitting diodes (CIE coordinates: x,=,0.282, y,=,0.336). In particular, white electroluminescence in a binary blend of a blue-emitting, organic-soluble rotaxane based on a polyfluorene derivative and the green-emitting poly(9,9-dioctylfluorene-alt-benzothiadiazole (F8BT) is achieved. Morphological and structural analyses by atomic force microscopy, fluorescence mapping, µ-Raman, and fluorescence lifetime microscopy are used to complement optical and electroluminescence characterization, and to enable a deeper insight into the properties of the novel blend. [source] Can the hybrid meta GGA and DFT-D methods describe the stacking interactions in conjugated polymers?JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2009Ahmed Dkhissi Abstract Newly developed hybrid meta density functionals and density functionals augmented by a classical London dispersion term have been systematically applied for the description of stacking energy and intermolecular distance of thiophene dimer and substituted thiophene dimer. The performance of the various approaches is compared with the benchmark ab-initio calculations done with CCSD(T) (Tsuzuki et al., JACS 2002, 124, 12200). Our results indicate that, contrary to the previous DFT methods which are not reliable, the new generation of DFT performs better the stacking interactions. These functionals, and especially those with an empirical correction, are suitable for general application in conducting polymers and, in particular, the modeling of solid state in which the overlap of ,-, interactions between the conjugated chains is important. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Determination of intermolecular distance for a model peptide of Bombyx mori silk fibroin, GAGAG, with rotational echo double resonanceBIOPOLYMERS, Issue 2 2002Tsunenori Kameda Abstract Rotational echo double resonance NMR spectroscopy is applied for the determination of the distance of intermolecular chains of pentapeptide, GAGAG (G: Gly, A: Ala), a model typical of the crystalline domain in Bombyx mori silk fibroin. 1:4 mixture of G[1- 13C]AGAG and GAG[15N]AG with antiparallel ,-sheet structure was used to determine the distance of intermolecular hydrogen bonding between adjacent molecules within pleated sheet and the 13C,15N interatomic distance was determined to be 4.3 Å. On the other hand, 1:4 mixture of GAG[1- 13C]AG and GAG[15N]AG gave information on the interpleated sheet arrangement. When we assumed the same distances between two interpleated sheets, the distance was calculated to be 5.3 Å and the angle 15N,13C,15N was 180°. © 2002 Wiley Periodicals, Inc. Biopolymers 64: 80,85, 2002 [source] X-ray and 13C solid-state NMR studies of N -benzoyl-phenylalanineCHEMICAL BIOLOGY & DRUG DESIGN, Issue 4 2000M.J. Potrzebowski Abstract: A crystalline sample of N -benzoyl- dl -phenylalanine 1 and a polycrystalline sample of N -benzoyl- l -phenylalanine 2 were studied using 13C high-resolution solid-state NMR spectroscopy. The X-ray structure of the dl form was established. Sample 1 crystallizes in a monoclinic form with a P21/c space group, a = 11.338(1) Å, b = 9.185(1) Å, c = 14.096(2) Å, ,,= 107.53(3)°, V = 1400(3) Å3, Z = 4 and R = 0.053. The principal elements of the 13C chemical shift tensors ,ii for 1 and 2, selectively 13C (99%) labeled at the carboxyl groups were calculated. On the basis of 13C ,ii analysis the hydrogen bonding pattern for sample 2 was deduced. Enriched samples were used to establish the intermolecular distance between chemically equivalent nuclei for 1 and spatial proximity in heterogeneous domain for 2, employing the ODESSA pulse sequence. The consistence of the complementary approach covering X-ray data, analysis of the 13C ,ii parameters and ODESSA results is revealed. [source] Oligomer-to-Polymer Transition in Short Ethylene Glycol Chains Connected to Mobile Hydrophobic AnchorsCHEMPHYSCHEM, Issue 1 2005Motomu Tanaka Dr. Abstract We studied the structure of short ethylene glycol (EG) chains with N repeating units (EGN, N=3, 6, 9, 12, and 15) connected to hydrophobic dihexadecyl chains by means of a combination of differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS/WAXS). These synthetic amphiphiles dispersed in water form planar lamellar stacks and hexagonal cylinders confining the EG chains to restricted geometries. Owing to the self-assembly of the anchoring points, the lateral density of EG chains in planar lamella can be quantitatively controlled. Furthermore, the chain-melting phase transition of the anchors enables us to "switch" the intermolecular distance reversibly. SAXS/WAXS results suggest that the shorter EG chains (N=3, 6, and 9) assume a helical conformation in stacks of planar lamella. When the EG chains are further elongated (N=12 and 15), the lamellar periodicities cannot be explained by a linear extrapolation of shorter oligomers, but can be interpreted well as polymer brushes following the scaling theorem. Such rich phase behaviors of EGN molecules can be used as a simple model of oligo/poly-saccharide chains on cell surfaces, which act not only as flexible repellers between neighboring cells but also as stable spacers for functional ligands. [source] Modeling high pressure reactivity in unsaturated systems: Application to dimethylacetyleneJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2009C. Mediavilla Abstract A general model is introduced to study pressure-induced reactivity on unsaturated systems in the condensed state. The model is applied here to dimethylacetylene (DMA) in the solid phase II (C/2m) because it has been proposed that two DMA molecules can react to form tetramethyl-cyclobutadiene (TMCBD). The proposed reaction process has been modeled by studying the structural and electronic changes undergone by two DMA molecules as they approach each other preserving the crystal symmetry of phase II. Both monodeterminantal (MP2 and DFT) and multideterminantal (CASSCF and MRMP2) methodologies were used to check the reliability of our model in predicting the reactivity of the system under compression. In all cases, structural results are in agreement with low-temperature diffraction experiments for the solid phase II. Our model indicates that DMA is expected to form the TMCBD dimer at intermolecular distances close to 2 Å. This value is in excellent agreement with previous calculations on the existence of long carbon,carbon bonds. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] An ab initio study of intermolecular interactions of nitromethane dimer and nitromethane trimerJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2003Jinshan Li Abstract Different geometries of nitromethane dimer and nitromethane trimer have been fully optimized employing the density functional theory B3LYP method and the 6-31++G** basis set. Three-body interaction energy has been obtained with the ab initio supermolecular approach at the levels of MP2/6-31++G**//B3LYP/6-31++G** and MP2/aug-cc-pVDZ//B3LYP/6-31++G**. The internal rotation of methyl group induced by intermolecular interaction has been observed theoretically. For the optimized structures of nitromethane dimer, the strength of CH,ON H-bond ranges from ,9.0 to ,12.4 kJ mol,1 at the MP2/aug-cc-pVDZ//B3LYP/6-31++G** level, and the B3LYP method underestimates the interaction strength compared with the MP2 method, while MP2/6-31++G**//B3LYP/6-31++G** calculated ,EC is within 2.5 kJ mol,1 of the corresponding value at the MP4(SDTQ)/6-31G**//B3LYP/6-31++G** level. The analytic atom,atom intermolecular potential has been successfully regressed by using the MP2/6-31++G**//B3LYP/6-31++G** calculated interaction energies of nitromethane dimer. For the optimized structures of nitromethane trimer the three-body interaction energies occupy small percentage of corresponding total binding energies, but become important for the compressed nitromethane explosive. In addition, it has been discovered that the three-body interaction energy in the cyclic nitromethane trimer is more and more negative as intermolecular distances decrease from 2.2 to 1.7 Å. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 345,352, 2003 [source] Pitfalls of data mining: triclinic polymorph of 2,2-aziridinedicarboxamide revisitedACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2007Marcin Podsiad Several procedures have been employed for validating structural models refined on poor quality single-crystal diffraction data. Analysis of intra- and intermolecular distances in the structures of 2,2-aziridinedicarboxamide polymorphs proved to be a robust means, and a means independent of the chosen unit cell and symmetry, of detecting several incorrect atom-type assignments in the reported structure of the triclinic polymorph of 2,2-aziridinedicarboxamide [Brückner (1982). Acta Cryst. B38, 2405,2408]. The corrected model, refined in the space group , rules out the existence of any conformational polymorphism in this compound. Small differences in the powder-diffraction patterns calculated for the original and corrected structures of the triclinic polymorph illustrate the sensitivity of the above method for polymorph validation. [source] catena -Poly[[bis(acetonitrile-,N)manganese(II)]-bis(,-trifluoromethanesulfonato-,2O:O,)]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2010Martin Lutz The title compound, [Mn(CF3SO3)2(CH3CN)2]n, has an MnII cation on an inversion centre in an octahedral environment. The trifluoromethanesulfonate anions act as bridging ligands and form a one-dimensional coordination polymer in the direction of the a axis. The F atoms of the trifluoromethanesulfonate anions form layers parallel to the ab plane, but despite short intermolecular distances, no stabilizing F...F interactions are detected. The Mn,N and C,C bonds of the acetonitrile ligand are analyzed according to the Hirshfeld rigid-bond test. Renninger effects in the reflection data are considered, explored and discussed. [source] 5-(4,5-Ethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalen-2-one (EDTO,TTP) and 5-[4,5-(ethene-1,2-diyldithio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalen-2-one (VDTO,TTP)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Hong-Feng Chen The title sulfur-rich organic molecular crystals, namely EDTO,TTP (C9H4OS8) and VDTO,TTP (C9H2OS8), are characterized by conjugated C,S bonds and S...S intermolecular short contacts. The planar EDTO,TTP molecules are parallel packed and exhibit strong intermolecular interactions, including side-by-side transverse S...S contacts, face-to-face longitudinal ,,, interactions and C,H...O hydrogen bonding. On cooling the EDTO,TTP crystal from 220 to 120,K, the cell dimensions and the intermolecular distances (such as S...S contacts and especially ,,, spacings) become shorter, while the intramolecular bonds become longer. The curved VDTO,TTP molecules are packed in such a way as to make the crystal fully depolarized. The intermolecular interactions of the VDTO,TTP crystal are relatively weak, because of the weak ,,, interactions and the lack of hydrogen bonding. [source] Coordination-Driven Hierarchical Organization of ,-Conjugated Systems: From Molecular to Supramolecular ,-Stacked AssembliesCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2010Yishan Yao Dr. Abstract The reaction of U-shaped, bimetallic, CuI complexes, assembled from a heteroditopic pincer, with cyano-capped ,-conjugated linkers gives a straightforward access to ,-stacked metallocyclophanes in good yields. In these assemblies, the ,-walls have an almost face-to-face arrangement. The versatility of this rational supramolecular synthesis is demonstrated with the use of linkers that have nanoscale lengths (up to 27.7,Å), different chemical compositions (oligo(para -phenylenevinylene)s OPVs, oligo(phenylene)s, oligo(phenylethynylene)s), and alternative geometries (linear, angular). Linkers that incorporate an internal pyridyne moiety can also be employed. X-ray diffraction studies revealed that the metallocyclophanes based on linear linkers self-organize into infinite ,-stacked columns in the solid state with intermolecular distances of about 3.6,Å. This approach, based on coordination-driven self-assembly, provides a novel and rational strategy for the stacking of extended ,-systems in the solid state. [source] | ||||||||||