Supramolecular daisy chains

Two series of self-complementary daisy chain monomers, in which a secondary ammonium ion-containing arm is grafted onto a macrocycle with either a [24 ]- or [25]crown-8 constitution, have been synthesized. In the solid- and 'g as'-phases, the parent [24]crown-8-based monomer forms dimeric superstructu res, as revealed by X-ray crystallography and mass spectrometry, respective ly. Elucidation of the complicated solution-phase behavior of this compound was facilitated by the synthesis and study of both deuterated, and fluorin ated, analogues. These investigations revealed that the cyclic dimeric supe rstructure also dominates in solution, except when extremes of either conce ntration (low), temperature (high), or solvent polarity (highly polar, e.g. , dimethyl sulfoxide) are employed. Whereas, upon aggregation, the [24]crow n-8-based daisy chain monomers have the capacity to form stereoisomeric sup erstructures further complicating the study of this series of compounds. Th e assembly of [25]crown-8-based monomers gives only achiral superstructures . The weaker association exhibited between secondary dialkylammonium ions a nd crown ethers with a [25]crown-8 constitution, however, resulted in limit ed oligomerization-only dimeric and trimeric superstructures were formed at experimentally attainable concentrations-of [25]crown-8-based daisy chain monomers.