Doped Mesoporous Silica Fibers: A New Laser Material

The fabrication of a laser based on mesoporous fibers is shown to be possible, demonstrating for the first time that mesostructural systems can be applied as advanced optical materials. The amplification of a guided mode in the fiber and the resulting, gain-narrowed emission (illustrated on the cover of this issue) are reported. It is stressed that the system used—a composite containing the dye rhodamine 6G—is a relatively simple type of laser material and better results can be expected in the future with different types of lasing guests in mesoporous fibers

Surfactant-directed syntheses of mesostructured zinc imidazolates: formation mechanism and structural insights

Supramolecular templating techniques have been widely used to direct the formation of porous materials with the goal of introducing permanent mesoporosity. While surfactant-directed self-assembly has been exploited for inorganic materials such as titania, silica, organosilica, and zeolites, it has rarely been applied to metal-organic frameworks (MOFs) and coordination polymers. Here we introduce a new family of gemini surfactant-directed zinc imidazolates, referred to as mesostructured imidazolate frameworks (MIFs), and present a detailed study on the influence of different gemini-type surfactants on the formation mechanism and structures of the resulting zinc imidazolates. The proposed formation mechanism for MIF-type materials involves co-assembly and crystallization processes that yield lamellar mesostructured imidazolate frameworks. Understanding and controlling such processes also has implications for the syntheses of microporous zinc imidazolate framework (ZIF) materials, whose formation can be suppressed in surfactant-rich solutions, whereas formation of MIF materials is favored in the presence of surfactants and triggered by the addition of halogenides. Solid-state 2D 13C1H HETCOR NMR measurements on prototypic CTAB-directed MIF-1 establish that the head group moieties of the surfactant molecules interact strongly with the zinc-imidazolate-bromide sheets. Additionally, the NMR analyses suggest that MIF-1 has a significant fraction of surfactant molecules that are interdigitated between the zinc-imidazolate-bromide sheets with an antiparallel stacking arrangement, consistent with the high thermal and chemical stability of the MIF hybrid materials

Determination of molecular orientational order in cold- stretched poly (p-phenylene vinylene) thin films by DECODER C- 13 NMR

The properties of polyp-phenylene vinylene) (PPV) films depend on the degree of orientational order present in the films. Recently, Dermaut et al. reported a novel cold-stretching technique (Macromolecules 33, 5634-5637 (2000)) in which chain alignment can be introduced into PPV precursor films by uniaxially stretching them prior to the thermal elimination reaction that forms PPV. The two-dimensional direction exchange with correlation for orientation-distribution evaluation and reconstruction (DECODER) C-13 NMR technique was applied to both unstretched PPV films and PPV films that were uniaxially cold stretched to a draw ratio lambda = l/l(0) = 5. The unstretched films were found to be moderately ordered, comprised of a component present at 80% with a Gaussian distribution of 60degrees fwhm, while the remaining 20% is isotropically distributed. A distribution of 9 3 fwhm was measured by NMR in good agreement with IR dichroism measurements for the uniaxially cold-stretched films, establishing that a high degree of orientational order can be introduced by cold stretching PPV films. (C) 2002 Elsevier Science (USA)

Surface effects on the structure and mobility of the ionic liquid C(6)C(1)ImTFSI in silica gels

We report on how the dynamical and structural properties of the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (C(6)C(1)ImTFSI) change upon different degrees of confinement in silica gels. The apparent diffusion coefficients of the individual ions are measured by H-1 and F-19 pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy, while the intermolecular interactions in the ionogels are elucidated by Raman spectroscopy. In addition, the local structure of the ionic liquid at the silica interface is probed by solid-state NMR spectroscopy. Importantly, we extend this study to a wider range of ionic liquid-to-silica molar ratios (x) than has been investigated previously, from very low (high degree of confinement) to very high (liquid-like gels) ionic liquid contents. Diffusion NMR measurements indicate that a solvation shell, with a significantly lower mobility than the bulk ionic liquid, forms at the silica interface. Additionally, the diffusion of the C(6)C(1)Im(+) and TFSI- ions decreases more rapidly below an observed molar ratio threshold (x < 1), with the intrinsic difference in the self-diffusion coefficient between the cation and anion becoming less pronounced. For ionic liquid molar ratio of x < 1, Raman spectroscopy reveals a different conformational equilibrium for the TFSI- anions compared to the bulk ionic liquid, with an increased population of the cisoid isomers with respect to the transoid. Concomitantly, at these high degrees of confinement the TFSI- anion experiences stronger ion-ion interactions as indicated by the evolution of the TFSI- characteristic vibrational mode at similar to 740 cm(-1). Furthermore, solid-state 2D Si-29{H-1} HETCOR NMR measurements establish the interactions of the ionic liquid species with the silica surface, where the presence of adsorbed water results in weaker interactions between Si-29 surface moieties and the hydrophobic alkyl protons of the cationic C(6)C(1)Im(+) molecules

Eutectic Syntheses of Graphitic Carbon with High Pyrazinic Nitrogen Content

Mixtures of phenols/ketones and urea show eutectic behavior upon gentle heating. These mixtures possess liquid-crystalline- like phases that can be processed. The architecture of phenol/ketone acts as structure-donating motif, while urea serves as melting-point reduction agent. Condensation at elevated temperatures results in nitrogen-containing carbons with remarkably high nitrogen content of mainly pyrazinic nature

Determination of molecular orientational order in cold- stretched poly (p-phenylene vinylene) thin films by DECODER C- 13 NMR

The properties of polyp-phenylene vinylene) (PPV) films depend on the degree of orientational order present in the films. Recently, Dermaut et al. reported a novel cold-stretching technique (Macromolecules 33, 5634-5637 (2000)) in which chain alignment can be introduced into PPV precursor films by uniaxially stretching them prior to the thermal elimination reaction that forms PPV. The two-dimensional direction exchange with correlation for orientation-distribution evaluation and reconstruction (DECODER) C-13 NMR technique was applied to both unstretched PPV films and PPV films that were uniaxially cold stretched to a draw ratio lambda = l/l(0) = 5. The unstretched films were found to be moderately ordered, comprised of a component present at 80% with a Gaussian distribution of 60degrees fwhm, while the remaining 20% is isotropically distributed. A distribution of 9 3 fwhm was measured by NMR in good agreement with IR dichroism measurements for the uniaxially cold-stretched films, establishing that a high degree of orientational order can be introduced by cold stretching PPV films. (C) 2002 Elsevier Science (USA)

Nanoscale insight into intermolecular interactions in organic photovoltaic blends using solid state NMR spectroscopy

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