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Self-Organization of Phthalocyanine-[60]Fullerene Dyads in Liquid Crystals
文摘
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The use of blends in which a mesogen induces mesomorphism into a non-mesogenic compound hasmade possible the self-organization of phthalocyanine-[60]fullerene (Pc-C60) dyads into liquid crystals.Pc-C60 dyads 1, 2, or 3, in which two photoactive units are brought together by a phenylenevinylenespacer, have been synthesized through a Heck reaction that links 4-vinylbenzaldehyde to a monoiodophthalocyanine precursor, followed by standard cycloaddition of azomethine ylides-generated from theformylPc derivative and N-methylglycine-to one of the double bonds of C60. The mesomorphic andthermal properties of different mixtures formed by the liquid-crystalline phthalocyanine 4 and dyads 1,2, or 3 were examined using polarizing optical microscopy (POM), differential scanning calorimetry(DSC), and X-ray diffraction (XRD). DSC diagrams of the blends show clear transitions from the crystallinestate to a mesophase, and the measured structural parameters obtained from the powder diffractionexperiments are consistent with a discotic hexagonal columnar (Colh) structure. Considering that segregationin domains of separated molecules of Pc-C60 dyad and phthalocyanine 4 would preclude mesomorphismdue to the mismatch in the column diameter and to the lack of mesogenic character of the pure dyads,a predominance of alternating stacking is proposed. Additionally, the observed decrease in the calculateddensity of the blend mesophases relative to the mesophase of pure compound 4 is important evidence inthis direction.
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