Supramolecularly Engineered π-Amphiphile

Abstract

This article describes self-assembly of supramolecularly engineered naphthalene-diimide (NDI)-derived amphiphiles NDI-1 and NDI-2. They have the same hydrophobic/hydrophilic balance but merely differ by a single functional group, amide or ester. They exhibit distinct self-assembly in water; NDI-1 forms hydrogel, which upon aging forms crystals, whereas NDI-2 forms micelles as revealed by in-depth structural analysis using cryo-TEM, dynamic light scattering, and small-angle X-ray scattering studies. These results suggest that the H-bonding among the amide groups fully regulates the self-assembly by overruling the packing parameters. Further, the present study elucidates sharp lower critical solution temperature exhibited by these π-amphiphiles, which has been extensively studied for many important applications of water-soluble polymers but hardly known in the literature of small-molecule surfactants. Control experiments with the same water-soluble hydrophilic wedge did not show such a property, confirming this to be a consequence of the supramolecular polymerization by extended amide–amide H-bonding and not inherent to the structure of the hydrophilic wedge containing oligo-oxyethylene chains.