Designing structural motifs for clickamers: exploiting the 1,2,3-triazole moiety to generate conformationally restricted molecular architectures

Noncovalent interactions, especially hydrogen-bonding interactions as well as electrostatic forces, confined within one macromolecule are the key to designing foldamers that adopt well-defined conformations in solution. In the context of significant recent activities in the area of triazole-connected foldamers, so-called clickamers, we present a fundamental study that compares various model compounds that bear adjacent N-, O-, or F-heteroatom substituents. The interplay of attractive and repulsive interactions leads to rotational constraints around the single bonds attached to both the 1- and 4-positions of the 1,2,3-triazole moiety and should therefore be able to induce well-defined conformational preferences in higher oligomers and polymers, that is, foldamers. Various compounds were synthesized and characterized with regard to their preferred conformations in all three aggregation states--that is, in the gas phase, in solution as well as in the solid state--by employing DFT calculations, NMR spectroscopic experiments, and X-ray crystallography, respectively. On the basis of the thus-obtained general understanding of the conformational behavior of the individual connection motifs, heterostructures were prepared from different motifs without affecting their distinct folding characteristics. Therefore, this work provides a kind of foldamer construction kit, which should enable the design of various clickamers with specific shape and incorporated functionality.