57 research outputs found

    Effect of Cross-Conjugation on Derivatives of Benzoisoindigo, an Isoindigo Analogue with an Extended π‑System

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    The effect of cross-conjugation on small molecule organic semiconductors derived from benzoisoindigo, a ring-expanded isoindigo derivative, is reported. In this work, 5-hexyl-2,2′-bithiophene was substituted at the cross-conjugated 5,5′-position of benzoisoindigo, yielding a new organic semiconductor with a donor–acceptor structure. The optoelectronic properties of this benzoisoindigo derivative were studied and compared with those of both linearly conjugated and cross-conjugated isoindigo-based analogues. Extending the conjugation of the electron-deficient isoindigo through ring fusion did substantially red-shift the absorption maximum of the highest occupied molecular orbital to lowest unoccupied molecular orbital transition; however, the cross-conjugation significantly reduced the oscillator strength. As a result, the photocurrent was significantly lower for organic photovoltaic devices made with cross-conjugated materials. This suggests that if synthetic methods to access the linearly conjugated 7,7′-derivatives can be developed, benzoisoindigo may be able to serve as a useful electron-deficient subunit in donor–acceptor systems

    Polymerization of Racemic 2,2′-Dialkyl-Sila[1]ferrocenophanes: DFT‑Assisted Polymer Analysis by <sup>29</sup>Si NMR Spectroscopy Using Model Compounds

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    The described research aimed at the preparation of racemic, C2 symmetric sila[1]ferrocenophanes with alkyl groups in 2,2′-positions to complement their known enantiopure counterparts. As the synthetic approach, the well-known Ugi amine chemistry was chosen to introduce planar chirality into the ferrocene framework. The challenge in this multistep process is the separation of a rac and meso mixture of diols obtained through the reduction of 1,1′-dialkanoylferrocenes by LiAlH4 or NaBH4. From the three tested alkanoyl groups, only one led to a significant excess of the rac diol, which could be separated by crystallizations and converted to rac-2,2′-diisobutyl-dimethylsila[1]ferrocene. Thermal ring-opening polymerization of this new monomer gave a poly(ferrocenylsilane) that consists of two types of diads, as revealed by two sets of peaks in its 29Si NMR spectrum centered at −5.66 and −7.74 ppm. 29Si NMR chemical shifts could be predicted with density functional theory (DFT) methods for planar-chiral bis(ferrocenyl)dimethylsilanes that were used to model these meso and racemo diads of the polymer. These calculations realistically predict that silicon atoms of racemo diads are higher shielded than those of meso diads. Surprisingly, the 29Si NMR peaks of both diads are split into a set of peaks, revealing a sensitivity of δ values beyond diads

    Experimental Verification of the Theory of Nuclear Quadrupole Relaxation in Liquids over the Entire Range of Molecular Tumbling Motion

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    Nuclear magnetic resonance (NMR) spectra of quadrupolar nuclei (<i>I</i> > 1/2) in liquids often consist of broad resonances, making it difficult to obtain useful chemical information. The poor NMR spectral resolution commonly observed for quadrupolar nuclei is a direct consequence of nuclear quadrupole relaxation processes. Although all key aspects of nuclear quadrupole relaxation processes have been known for decades within the framework of the Redfield relaxation theory, direct experimental NMR relaxation data that cover a wide range of molecular motion in liquids for quadrupolar nuclei are generally lacking. Here we report a complete set of experimental nuclear quadrupole relaxation data that are obtained for <sup>17</sup>O, a half-integer quadrupolar nucleus, over the entire range of molecular motion within the limit of the Redfield theory. A general approach utilizing the quadrupole relaxation properties in the slow motion limit will be particularly beneficial for studies of quadrupolar nuclei in biomolecules of medium and large sizes

    Brilliant Structurally Colored Films with Invariable Stop-Band and Enhanced Mechanical Robustness Inspired by the Cobbled Road

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    Recently, structural colors have attracted great concentrations because the coloration is free from chemical- or photobleaching. However, the color saturation and mechanical robustness are generally competitive properties in the fabrication of PCs (photonic crystals) films. Besides, the structure of PCs and their derivatives are easy to be invaded by liquids and lead to band gap shifts due to the change of refractive index or periodicity. To solve those problems, we infiltrate polydimethylsiloxane (PDMS) into the intervals between regularly arrayed hollow SiO<sub>2</sub> nanospheres, inspired by the cobbled road prepared by embedding stone in the bulk cement matrix. Consequently, the as-prepared PCs films show brilliant colors, invariable stop-bands, and excellent mechanical robustness. Moreover, the water contact angle even reached 166° after a sandpaper abrasion test. The combination of brilliant colors, invariable stop-bands, and excellent robustness is significant for potential application in paint and external decoration of architectures

    Corneal thickness in the entral (2-mm diameter), para-central (2 to 5-mm diameter), and peripheral (5 to 6-mm diameter) areas according to age interval in 614 normal Chinese children.

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    <p>Corneal thickness in the entral (2-mm diameter), para-central (2 to 5-mm diameter), and peripheral (5 to 6-mm diameter) areas according to age interval in 614 normal Chinese children.</p

    Corneal thickness in the central (2-mm diameter), para-central (2 to 5-mm diameter), and peripheral (5 to 6-mm diameter) areas, according to gender in 614 normal Chinese children.

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    <p>Corneal thickness in the central (2-mm diameter), para-central (2 to 5-mm diameter), and peripheral (5 to 6-mm diameter) areas, according to gender in 614 normal Chinese children.</p

    Corneal thickness in the central (2-mm diameter), para-central (2 to 5-mm diameter), and peripheral (5 to 6-mm diameter) areas, according to the quartile corneal curvature radius in normal Chinese children (n = 370).

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    <p>Corneal thickness in the central (2-mm diameter), para-central (2 to 5-mm diameter), and peripheral (5 to 6-mm diameter) areas, according to the quartile corneal curvature radius in normal Chinese children (n = 370).</p

    Corneal Thickness Measured by RTVue Fourier Optical Coherence Tomography for 614 Chinese Children (Mean (SD)).

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    <p>The average corneal thickness (SD) for 614 Chinese Children in the left eye (Left) and the right eye (Right). S: Superior, ST: Superior Temporal, ST: Temporal, IT: Inferior Temporal, I: Inferior, IN: Inferior Nasal, N: Nasal, SN: Superior Nasal. SD: Standard Deviation.</p

    Scatter plot of the position of minimum corneal thickness in the left eyes of 614 normal Chinese children.

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    <p>Along the verticat axis, a negative number represents the distance inferior to the pupil center, while a positive number represents the distance superior to the pupil center (μm). Along the horizontal axis, a negative number represents the distance temporal to the pupil center, while a positive number represents the distance nasal to the pupil center (μm).</p
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