Influence of the Z/E Isomerism on the Pathway Complexity of a Squaramide‐Based Macrocycle. Issue 7 (15th January 2021)

• Record Type: Journal Article
• Authors: Orvay, Francisca; Cerdá, Jesús; Rotger, Carmen; Ortí, Enrique; Aragó, Juan; Costa, Antonio; Soberats, Bartolome
• Is Part Of: Small. Volume 17:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-01-15
• Subjects: conformational isomerism -- hydrogen bonding -- pathway complexity -- squaramides -- supramolecular polymers; Nanotechnology -- Periodicals; Nanoparticles -- Periodicals; Microtechnology -- Periodicals; 620.5
• DOI: 10.1002/smll.202006133
• Languages: English
• ISSNs: 1613-6810

Abstract

Abstract: The rising interest on pathway complexity in supramolecular polymerization has prompted the finding of novel monomer designs able to stabilize kinetically trapped species and generate supramolecular polymorphs. In the present work, the exploitation of the Z/E (geometrical) isomerism of squaramide (SQ) units to produce various self‐assembled isoforms and complex supramolecular polymerization pathways in methylcyclohexane/CHCl3 mixtures is reported for the first time. This is achieved by using a new bissquaramidic macrocycle (MSq ) that self‐assembles into two markedly different thermodynamic aggregates, AggA (discrete cyclic structures) and AggB (fibrillar structures), depending on the solvent composition and concentration. Remarkably, UV–vis, 1 H NMR, and FT‐IR experiments together with quantum‐chemical calculations indicate that these two distinct aggregates are formed via two different hydrogen bonding patterns (side‐to‐side in AggA and head‐to‐tail in AggB ) due to different conformations in the SQ units ( Z, E in AggA and Z, Z in AggB ). The ability of MSq to supramolecularly polymerize into two distinct aggregates is utilized to induce the kinetic‐to‐thermodynamic transformation from AggA to AggB, which occurs via an on‐pathway mechanism. It is believed that this system provides new insights for the design of potential supramolecular polymorphic materials by using squaramide units. Abstract : Newly designed squaramide‐based macrocycle exhibits pathway complexity behavior due to Z/E isomerism of the squaramide units. While the Z, E isomer self‐assembles into cyclic nanostructures (AggA ) via side‐to‐side hydrogen bonds, the Z, Z isomer forms fibers (AggB ) by head‐to‐tail interactions. Remarkably, the kinetic‐to‐thermodynamic (AggA ‐to‐AggB ) transformation occurs via an on‐pathway mechanism involving significant changes at molecular, supramolecular, and macroscopic level.