In
this Perspective, we present a unique approach to the design and synthesis
of giant molecules based on “nanoatoms”
for engineering structures across multiple length scales and controlling
their macroscopic properties. Herein, “nanoatoms” refer
to shape-persistent molecular nanoparticles (MNPs) with precisely
defined chemical structures and surface functionalities that can serve
as elemental building blocks for the precision synthesis of giant
molecules by methods such as sequential “click” approach. Typical “nanoatoms”
include those MNPs based on fullerenes, polyhedral oligomeric silsesquioxanes,
polyoxometalates, and folded globular proteins. The resulting giant
molecules are precisely defined macromolecules. They include,
but are not limited to, giant surfactants, giant shape amphiphiles,
and giant polyhedra. Giant surfactants are polymer tail-tethered “nanoatoms”
where the two components have drastic chemical differences to impart
amphiphilicity. Giant shape amphiphiles not only are built up by covalently
bonded MNPs of distinct shapes where the self-assembly is driven by
chemical interactions but also are largely influenced by the packing
constraints of each individual shape. Giant polyhedra are either made
of a large MNP or by deliberately placing “nanoatoms”
at the vertices of a polyhedron. In general, giant molecules capture
the essential structural features of their small-molecule counterparts
in many ways but possess much larger sizes. They are recognized in
certain cases as size-amplified versions of those counterparts, and
often, they bridge the gap between small molecules and traditional
macromolecules. Highly diverse, thermodynamically stable and metastable
hierarchal structures are commonly observed in the bulk, thin film,
and solution states of these giant molecules. Controlled structural
variations by precision synthesis further reveal a remarkable sensitivity
of their self-assembled structures to the primary chemical structures.
Unconventional nanostructures can be obtained in confined environments
or through directed self-assembly. All the results demonstrate that
MNPs are unique elements for macromolecular science, providing a versatile
platform for engineering nanostructures that are not only scientifically
intriguing but also technologically relevant.