Supramolecular Janus Nanocylinders: Solvent-Induced Hydrogen-Bond Modulation Yields Structures under Thermodynamic Equilibrium

Abstract

Janus nanocylinders (JNCs) are anisotropic, non-centrosymmetric colloids composed of two different faces, making them attractive for advanced functional materials. However, their nanometric dimensions and pronounced anisotropy complexify their preparation. Recently, a versatile supramolecular strategy has emerged that enables JNCs to be formed without the need for incompatible polymer arms. It occurs in water via the self-assembly of two polymers end-functionalized with complementary, non-symmetrical, hydrogen-bonding motifs. However, assembly in water is driven by a combination of hydrogen bonds and strong hydrophobic effects, yielding kinetically frozen nanostructures whose amount and dimensions depend on the assembly process. Here, we show that supramolecular assembly in toluene overcomes these limitations. In contrast to aqueous systems, solvophobic effects are negligible in toluene, and supramolecular assembly is predominantly driven by the formation of hydrogen bonds between urea-associating units. Consequently, reorganization of the assemblies is possible in toluene at room temperature and a pathway-independent supramolecular organization can be achieved by modulating intermolecular interactions through heating or by the addition of a moderate hydrogen-bond competitor. These results hint at the formation of supramolecular Janus nanocylinders at thermodynamic equilibrium, which can be formed in a very straightforward direct dispersion approach with repeatable characteristics (length, diameter).