Flipping Motion To Bias the Organized Supramolecular Polymerization of N-Heterotriangulenes

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Synergistic experimental and theoretical studies have allowed the disentangling of the possible pathways for the supramolecular polymerization of a series of dicyanovinyl-bridged N-heterotriangulene (NHT) derivatives bearing benzamide units with achiral (1a) and chiral (1b,c) side chains. The synthesis of these bowl-shaped, self-assembling units yields a mixture of monomeric species with C3- and C1-symmetry. Both monomeric species are able to self-assemble into different supramolecular aggregates with sufficient stability to coexist in freshly prepared solutions. The dissimilar ratio of the aggregates initially generated results in different spectroscopic features and, more specifically, in the apparition of nonmirror circular dichroism (CD) spectra for chiral 1b and 1c. The interconversion at room temperature of the aggregates formed by the C3- and C1-symmetry monomeric species is energetically unfavorable due to the steric hindrance between the neighboring dicyanovinyl groups within the aggregate. Heating the aggregates constituted by both monomeric species favors their disassembly and, at the same time, the conversion of the monomeric species with C1-symmetry into that with C3-symmetry by a flipping motion of one dicyanovinyl group. Cooling down the solutions back to room temperature leads to the formation of helical-like columnar aggregates based on C3-symmetry monomers showing specular CD spectra for chiral 1b and 1c. The flipping motion at the molecular level described here for the bowl-shaped dicyanovinyl-bridged NHTs 1a–c is, to the best of our knowledge, the only example in which a geometric change in the monomeric species, with no participation of intramolecular noncovalent interactions, is responsible for biasing the pathway complexity that yields two different stable supramolecular architectures from a single self-assembling unit.