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The synthesis of a series of shape-persistent macrocycles (SPMs) (1–4 and 6) comprising different numbers and/or spatial arrangement of meta-substituted tetrafluorobenzene and benzene subunits interlinked with diacetylenes is described. To increase their solubility, all five SPMs were functionalized by four peripheral hexyl chains. These SPMs were assembled from common diacetylene building blocks by a modular synthetic strategy based on palladium and/or copper catalyzed versions of acetylene coupling reactions (oxidative acetylene coupling and Cadiot–Chodkiewicz coupling). The aggregation properties in chloroform of SPMs1–6 were investigated by concentration- and temperature-dependent 1H-NMR investigations and by vapour pressure osmometry studies. Aggregation constants and thermodynamic data of the process were obtained by least-squares fitting of the NMR data and by van't Hoff analysis respectively. Aggregation was only observed for SPMs2–6 comprising electron deficient tetrafluorobenzene corner units. While dimerization was the major aggregation process for SPMs3–6, the formation of larger aggregates in solution was only observed for SPM2. The formation of aggregates is in all cases enthalpically driven. As the largest and the smallest enthalpic contribution and entropic loss in the series of aggregating SPMs were found for the two SPMs3 and 4, each comprising two fluorinated corner units, the spatial arrangement of these subunits within the macrocycle seems to be at least equally important as the ratio of tetrafluorobenzene and benzene moieties. Interestingly, micro-scaled hexagonal rods were formed from SPM3 upon heating in toluene, presumably consisting of mixtures of oligomers arising from covalently interlinked macrocycles.
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Organic & Biomolecular Chemistry
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