title: Aromatic Gain in a Supramolecular Polymer.
abstract: The synergy of aromatic gain and hydrogen bonding in a supramolecular polymer is explored. Partially aromatic bis(squaramide) bolaamphiphiles were designed to self-assemble through a combination of hydrophobic, hydrogen-bonding, and aromatic effects into stiff, high-aspect-ratio fibers. UV and IR spectroscopy show electron delocalization and geometric changes within the squaramide ring indicative of strong hydrogen bonding and aromatic gain of the monomer units. The aromatic contribution to the interaction energy was further supported computationally by nucleus-independent chemical shift (NICS) and harmonic oscillator model of aromaticity (HOMA) indices, demonstrating greater aromatic character upon polymerization: at least 30% in a pentamer. The aromatic gain-hydrogen bonding synergy results in a significant increase in thermodynamic stability and a striking difference in aggregate morphology of the bis(squaramide) bolamphiphile compared to isosteres that cannot engage in this effect.
authors.affiliation: Department of Supramolecular and Biomaterials Chemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden (The Netherlands).
authors.forename: Victorio
authors.initials: V
authors.lastname: Saez Talens
authors.affiliation: Process & Energy Laboratory, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft (The Netherlands).
authors.forename: Pablo
authors.initials: P
authors.lastname: Englebienne
authors.affiliation: Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim (Norway).
authors.forename: Thuat T
authors.initials: TT
authors.lastname: Trinh
authors.affiliation: Department of Supramolecular and Biomaterials Chemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden (The Netherlands).
authors.forename: Willem E M
authors.initials: WE
authors.lastname: Noteborn
authors.affiliation: Department of Chemical Engineering and Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (The Netherlands).
authors.forename: Ilja K
authors.initials: IK
authors.lastname: Voets
authors.affiliation: Department of Supramolecular and Biomaterials Chemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden (The Netherlands). r.e.kieltyka@chem.leidenuniv.nl.
authors.forename: Roxanne E
authors.initials: RE
authors.lastname: Kieltyka
keywords: aromaticity; non-covalent interactions; self-assembly; squaramides; supramolecular polymers