Flexible Chirality in Self‐Assembled N‐Annulated Perylenedicarboxamides

N‐annulated perylenedicarboxamides 1–3 form supramolecular polymers with a strong tendency to aggregate. The bundles of fibers formed generate a spontaneous anisotropy that conditions the chiroptical features of the described molecules in solution; a strong linear dichroism effect accompanies the circular dichroism (CD) outcome. There is no influence of the point chirality existing at the side chains of 1 and 2 , and these molecules present the same chiroptical features as achiral 3 . Mechanical rotary stirring increases the CD response and the sign of the dichroic signal changes with the stirring direction. Theoretical calculations indicate that the self‐assembly of 1–3 in helical columnar stacks generates atropisomers by the restricted rotation of the H‐bonded benzamide units. Molecular mechanics/molecular dynamics calculations predict a feasible intrastack stereomutation of the helical aggregates due to the rapid rupture/formation of the amide H‐bonds. This oscillating helicity, together with the fact that right‐ and left‐handed helices are predicted to be mostly isoenergetic, justifies the negligible contribution of the molecular chirality embedded in the paraffinic side chains of 1 and 2 . The reported CD behavior contributes to shed light on the physical processes promoting flexible macroscopic chirality that, in turn, can be utilized for the spectroscopic visualization of torsional flows generated in a vortex.     

Supramolecular Polymers: Rigid Dimers Formed through Strong Interdigitated H‐Bonds Yield Compact 1D Supramolecular Helical Polymers (Small 3/2011)

Hierarchical self‐assembly of small abiotic molecular modules interacting through noncovalent forces is increasingly being used to generate functional structures and materials for electronic, catalytic, and biomedical applications. The greatest control over the geometry in H‐bond supramolecular architectures, especially in H‐bonded supramolecular polymers, can be achieved by using conformationally rigid molecular modules undergoing self‐assembly through strong H‐bonds. Their binding strength depends on the multiplicity of the H‐bonds, the nature of donor/acceptor pairs and their secondary attractive/repulsive interactions. Here a functionalized molecular module is described, which is capable of self‐associating through self‐complementary H‐bonding patterns comprising four strong and two medium‐strength H‐bonds to form dimers. The self‐association of these phenylpyrimidine‐based dimers through directional H‐bonding between two lateral pyridin‐2(1H)‐one units of neighboring molecules allows the formation of highly compact 1D supramolecular polymers by self‐assembly on graphite. A concentration‐dependent study by scanning tunneling microscopy at the solid–liquid interface, corroborated by dispersion‐corrected density functional studies, reveals the controlled generation of either linear supramolecular 2D arrays, or long helical supramolecular polymers with a high shape persistence.     

Tunable Energy Landscapes to Control Pathway Complexity in Self‐Assembled N‐Heterotriangulenes: Living and Seeded Supramolecular Polymerization

Herein, the synthesis and self‐assembling features of N‐heterotriangulenes 1 – 3 decorated in their periphery with 3,4,5‐trialkoxy‐N‐(alkoxy)benzamide moieties that enable kinetic control of the supramolecular polymerization process are described. The selection of an appropriate solvent results in a tunable energy landscape in which the relative energy of the different monomeric or aggregated species can be regulated. Thus, in a methylcyclohexane/toluene (MCH/Tol) mixture, intramolecular hydrogen‐bonding interactions in the peripheral side units favor the formation of metastable inactivated monomers that evolve with time at precise conditions of concentration and temperature. A pathway complexity in the supramolecular polymerization of 1 – 3 cannot be determined in MCH/Tol mixtures but, importantly, this situation changes by using CCl₄. In this solvent, the off‐pathway product is a face‐to‐face H‐type aggregate and the on‐pathway product is the slipped face‐to‐face J‐type aggregate. The autocatalytic transformation of the metastable monomeric units, as well as the two competing off‐ and on‐pathway aggregates allow the realization of seeded and living supramolecular polymerizations. Interestingly, the presence of chiral, branched side chains in chiral ( S )‐ 2 noticeably retards the kinetics of the investigated transformations. This work brings to light the relevance of controlling the pathway complexity in self‐assembling units and opens new avenues for the investigation of complex and functional supramolecular structures.