Long-range ordered columns of a hexabenzo[bc,ef,hi,kl,no,qr]coronene–polysiloxane complex: towards molecular nanowires

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Abstract
The complexation of a carboxylate functionalized hexabenzocoronene with an amino functionalized polysiloxane results in a polymeric complex, which forms two highly ordered discotic columnar liquid crystalline structures Col1 and Col2. By using small-angle X-ray scattering it was shown that four columns per unit cell are two-dimensionally ordered in oblique lattices. An order–order transition from Col1 to Col2 was detected at about 90°C. The lattice constants of Col1 are a = b = 5.0 nm and γ = 112°, that of Col2 are a = b = 5.5 nm and γ = 108°. As a structural consequence to the complexation the heights of the columns within these phases are remarkably large. The heights were estimated using electron microscopy to be in the range of at least 200 nm which is more than 100 times their diameter (1.4 nm). The disc-like aromatic cores are arranged tilted with respect to the column axis in Col1 and with low intracolumnar ordering. By contrast the cores are oriented perpendicular to the column axis in the Col2 phase. Here a sharp intracolumnar reflection is present which results from a well-defined disc distance of 0.35 nm with strong π–π interactions. The mechanical properties of the highly flexible complex material were investigated using dynamic mechanical analysis and its thermal properties using differential calorimetry. Such polymeric complex nanostructures, which contain a hierarchy of three incompatible elements (aromatic cores are embedded in a matrix of alkyl chains which itself is embedded in a matrix of polysiloxane), could be useful for the fabrication of molecular nanowires.

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