Crystal Engineering of Supramolecular 1,4‐Benzene Bisamides by Side‐Chain Modification – Towards Tuneable Anisotropic Morphologies and Surfaces

• Published in: Chemphyschem Vol. 22; no. 24; pp. 2585 - 2593
• Main Authors: Zwan, Kasper P., Steinlein, Christoph, Kreger, Klaus, Schmidt, Hans‐Werner, Senker, Jürgen
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 13.12.2021; John Wiley and Sons Inc
• Subjects: ab initio structure solution; Asymmetry; Benzene; Chains; Crystal structure; Crystals; DFT calculations; Exposure; Hydrocarbons; Hydrophobicity; Molecular structure; Morphology; NMR crystallography; NMR spectroscopy; Platelets; self-assembly; Substitutes; supramolecular polymer additives; Surface properties; Wetting; supramolecular polymer additives; NMR crystallography; ab initio structure solution; self-assembly; DFT calculations
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.202100597

Benzene bisamides are promising building blocks for supramolecular nano‐objects. Their functionality depends on morphology and surface properties. However, a direct link between surface properties and molecular structure itself is missing for this material class. Here, we investigate this interplay for two series of 1,4‐benzene bisamides with symmetric and asymmetric peripheral substitution. We elucidated the crystal structures, determined the nano‐object morphologies and derived the wetting behaviour of the preferentially exposed surfaces. The crystal structures were solved by combining single‐crystal and powder X‐ray diffraction, solid‐state NMR spectroscopy and computational modelling. Bulky side groups, here t‐butyl groups, serve as a structure‐directing motif into a packing pattern, which favours the formation of thin platelets. The use of slim peripheral groups on both sides, in our case linear perfluorinated, alkyl chains, self‐assemble the benzene bisamides into a second packing pattern which leads to ribbon‐like nano‐objects. For both packing types, the preferentially exposed surfaces consist of the ends of the peripheral groups. Asymmetric substitution with bulky and slim groups leads to an ordered alternating arrangement of the groups exposed to the surface. This allows the hydrophobicity of the surfaces to be gradually altered. We thus identified two leitmotifs for molecular packings of benzene bisamides providing the missing link between the molecular structure, the anisotropic morphologies and adjustable surface properties of the supramolecular nano‐objects. The crystal structures of two series of 1,4‐benzene bisamides with symmetric and asymmetric peripheral substitution were solved by NMR crystallography. The authors found that the bulkiness of the side groups guides the supramolecular self‐assembly into one of two specific packing patterns. Their anisotropic crystal‐growth behavior results in a defined nano‐object morphology. Slim side chains, in our case perfluorinated alky chains, led to ribbon‐like nano‐objects, whereas bulky side chains led to thin platelets.