Guest Controlled Assembly of Gold Nanoparticles Coated with Calix[4]arene Hosts

Gold nanoparticles protected with thiolate Calix[4]arenes hosts were synthesized through an exchange reaction in toluene, starting from tetraoctyl ammonium bromide stabilized gold nanoparticles having a mean core size of ∼6 nm. In low polar solvents, these new Calix[4]arene-coated nanoparticles are able to self-assemble through supramolecular interactions with dialkyl dipyridinium-based guests (2−3). The guest-induced self-assembly process between nanoparticles has been studied using UV−vis spectroscopy, dynamic light scattering, and TEM measurements. The size and the solubility of the aggregates strongly depend on the length and rigidity of the bifunctional guest used as “supramolecular linker” between the nanoparticles. In particular, the long and flexible guest 2 gives rise to superaggregates of nanoparticles that remain soluble in common low polar solvents.