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| - 3-Hexyl Tetra-Substituted Sesquithienylene−PhenylenePolyazomethines with High Molecular Weight. MechanisticConsiderations
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| - The synthesis and characterization of copolymersconstituted by the periodic alternationof six thienylenic and two phenylenic moieties linked by azomethinegroups are reported. The azeotropicpolycondensation used for this preparation yields higher molecularweight but sterically more disorderedcopolymers. By 1H NMR experiments syn and anti isomersat imine linkages were evidenced. Mechanisticconsiderations on the different synthetic routes followed inpolyazomethine preparation imply the lackof a polar control on the formation of the syn isomer. Thecapability of the substituents to rotate aroundthe C−N bond of the intermediate is related to the overall bulkinessof the molecules. Due to theirmolecular weight, optical quality films were obtained eitherfree-standing or spin-coated from tetrachloroethane solutions. The solid-state aggregation was investigated byXRD techniques, indicating forproperly annealed samples some liquid crystal character, in agreementwith microscopy observations; infact a smectic or nematic arrangement was detected as a function of syncontent. A proper control ofanti/syn content in the copolymer allows a noticeable tuning in thephotoluminescence spectra.
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