Spontaneous Formation of Highly Stable Nanoparticle Supercrystals Driven by a Covalent Bonding Interaction.

Nanoparticle supercrystals (NPSCs) are of great interest as materials with emergent properties. Different types of intermolecular forces, such as van der Waals interaction and hydrogen bonding, are present in the NPSCs fabricated to date. However, the limited structural stability of such NPSCs that results from the weakness of these intermolecular forces is a challenge. Here, we report a spontaneous formation of NPSCs driven by covalent bonding interactions, a type of intramolecular force much stronger than the above-mentioned intermolecular forces. A model solution-phase anhydride reaction is used to form covalent bonds between molecules grafted on the surface of gold nanoparticles, resulting in three-dimensional NPSCs. The NPSCs are very stable in different solvents, in dried conditions, and at temperatures as high as 160 °C. In addition to this, the large library of covalent-bond-forming reactions available and the low cost of reactants make the covalent bonding approach highly versatile and economical.