Molecular Engineering of the Kinetic Barrier in Seeded Supramolecular Polymerization.

Seeded supramolecular polymerization (SSP) is a method that enables the controlled synthesis of supramolecular structures. SSP often relies on structures that are capable of self-assembly by interconverting between intramolecular and intermolecular modes of hydrogen bonding, characterized by a given kinetic barrier that is typically low. The control of the polymerization process is thus limited by the propensity of the hydrogen bonds to interconvert between the intramolecular and intermolecular modes of binding. Here, we report on an engineering of the polymerization kinetic barriers by sophisticated molecular design of the building blocks involved in such SSP processes. Our designs include two types of intramolecular hydrogen-bonded rings: on one hand, a central triazine tricarboxamide moiety that prevents self-assembly due to its stable intramolecular hydrogen bonds and on the other hand, three peripheral amide groups that promote self-assembly due to their stable intermolecular hydrogen bonds. We report a series of molecules with increasing bulkiness of the peripheral side chains exhibiting increasing kinetic stability in the monomeric form. Owing to the relative height of the barrier, we were able to observe that the rate constant of seeding is not proportional to the concentration of the seeds used. Based on that, we proposed a new kinetic model in which the rate-determining step is the activation of the monomer, and we provide the detailed energy landscape of the supramolecular polymerization process. Finally, we investigated the hetero-seeding of the building blocks that shows either inhibition or triggering of the polymerization.

Orchestrating Communications in a Three-Type Chirality Totem: Remote Control of the Chiroptical Response of a Möbius Aromatic System.

Among the various types of chirality (central, axial, helical, planar, etc.), that inherent to Möbius topology remains almost unexplored, partly due to the difficulty to access Möbius compounds. Over the past decade, [28]hexaphyrins have been revealed to be among the best candidates to build on Möbius aromaticity. Whereas their flexibility needs to be controlled to get P/M twist enantioselectivity, it could be of great interest to sustain dynamic chirality transfer. In this context, we report herein the first example of a Möbius aromatic ring capped by a cavity, consisting of a Möbius [28]hexaphyrin doubly linked to an α-cyclodextrin. This unique design affords a "totem" of three different chirality elements arising from the cyclodextrin (fix central chirality), the bridging pattern (dynamic planar chirality), and the hexaphyrin (dynamic topological chirality). Chirality transfers (as shown in the TOC graphic) are characterized by a stereospecific planar-to-topological communication (diastereomeric excess >95%; the highest asymmetric selectivity reported to date for a Möbius ring) combined to a stereoselective central-to-planar communication (up to 60% diastereomeric excess). Interestingly, the stereoselectivity is remotely controlled by coordination of an achiral effector to the hexaphyrin, increasing up to 5 times the chiroptical response of the Möbius aromatic π-system. These results highlight the advantageous use of dynamic chirality transfers to further incorporate Möbius chirality and aromaticity into all kinds of stimuli-responsive devices.