Theory predicts that cyanine dyes and related linear systems
undergo symmetry collapse and bond
localization at long chain lengths. Beyond this “cyanine
limit”, the properties of these systems do not
extrapolate
from their shorter counterparts. To test this prediction,
dipyridocyanines have been synthesized and shown to
undergo
such symmetry collapse with chain lengths as short as 13.
Smectic A (S A ) liquid crystalline phase developed from a new kind of mesogen-jacketed liquid crystalline polymer (MJLCP) whose mesogenic side groups are asymmetrically bonded to the main-chain was first reported. Two series of MJLCPs, poly[4,4′-bis(4-butoxyphenyloxycarbonyl)-2-vinylbiphenyl] (PBP2VBP) and poly[4,4′-bis(4-butoxyphenyloxycarbonyl)-3-vinylbiphenyl] (PBP3VBP) with different molecular weights were designed and synthesized Via atom transfer radical polymerization successfully. The chemical structures of the monomers were confirmed by elemental analysis, mass spectrometry and 1 H NMR. The molecular characterization of the polymers was performed with 1 H NMR, gel permeation chromatography, and thermogravimetric analysis. Their phase structures and transitions were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and polarized light microscopy experiments. The experimental results suggest that the polymer (PBP2VBP and PBP3VBP) with asymmetry mesogenic core can develop into a well-defined smectic A (S A ) phase. This implies that the polymer molecules in the LC phase can be more ribbonlike rather than rodlike.
Exploring new routes to lock the dynamic C=N bonds in imine-linked covalent organic frameworks (COFs) is highly desired for enhancing their stability and functionality. Herein, a novel C=N bridge locking strategy via rhodium-catalyzed [4+2] annulation is developed to construct nonsubstituted quinoline-linked COFs (NQ-COFs). The notable feature of this strategy includes high C=N conversion efficiency, oxidant-free, and generality for synthesis of a variety of NQ-COFs with high chemical stability. Particularly, after postsynthetic modification, the crystallinity, topology, and porosity of pristine imine-linked COFs are well retained. When used as photocatalysts, NQ-COFs display better visible light absorption and carriers' separation efficiency due to enhanced in-plane π conjugation ability, as well as more facile generation of superoxide anion radicals than their counterparts, thus leading to efficient synthesis of 2,4,6-tris(aryl)pyridines, benzimidazole, and sulfoxide derivatives.
Irreversible locking of imine linkage into stable linkages represents a promising strategy to improve the robustness and functionality of covalent organic frameworks (COFs). We report, for the first time, a...
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