Towards supramolecular nanostructured materials: control of the self-assembly of ionic bent-core amphiphiles

Abstract

Control of the bottom-up self-assembly of ionic bent-core dendrimers has been systematically studied by molecular design. This process gave rise to architectures with diverse packing, shapes and dimensions to construct structured materials at the nanoscale. The compact organization of the molecules achieved in bent-core mesophases was transferred or induced to self-assemblies in the presence of water – even in the case of non-mesogenic dendrimers. The subtle balance of molecule–molecule and molecule–solvent interactions regulated the morphology of the aggregates and these ranged from rods, non-twisted or twisted fibers, helical ribbons and nanotubes. The structure obtained was dependent on the choice of dendritic nucleus, the bent-core structure (from 5 to 3 aromatic ring systems), the lateral moiety and the length of the outer flexible tails. The rigid nature of the chemical structure controlled the type of molecular packing in the layers and allowed molecular conformational chirality to be transmitted to the supramolecular aggregates, despite achiral molecules being used. The short/long terminal chain lengths determined the type of curvature of the ribbons. Some of these self-assemblies are proposed as alternatives to the attractive and widely applied helical nanofilaments formed by bent-core mesogens, but, thanks to their amphiphilic nature, the novel compounds can be processed from solution. Moreover, the self-assembly process was studied in an effort to elucidate the aggregation mechanism of these bent-shaped amphiphiles and to define experimental protocols to provide high quality and homogeneous aggregates.