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.

A novel giant surfactant possessing a well-defined hydrophilic head and a hydrophobic polymeric tail, polystyrene-(carboxylic acid-functionalized polyhedral oligomeric silsesquioxane) conjugate (PS-APOSS), has been designed and synthesized via living anionic polymerization, hydrosilylation, and thiol-ene "click" chemistry. PS-APOSS forms micelles in selective solvents, and the micellar morphology can be tuned from vesicles to wormlike cylinders and further to spheres by increasing the degree of ionization of the carboxylic acid. The effect of APOSS-APOSS interactions was proven to be essential in the morphological transformation of the micelles. The PS tails in these micellar cores were found to be highly stretched in comparison with those in traditional amphiphilic block copolymers, and this can be explained in terms of minimization of free energy. This novel class of giant surfactants expands the scope of macromolecular amphiphiles and provides a platform for the study of the basic physical principles of their self-assembly behavior.

This paper reports a comprehensive study on the synthesis and self-assembly of two model series of molecular shape amphiphiles, namely, hydrophilic [60]fullerene (AC(60)) tethered with one or two polystyrene (PS) chain(s) at one junction point (PS(n)-AC(60) and 2PS(n)-AC(60)). The synthesis highlighted the regiospecific multiaddition reaction for C(60) surface functionalization and the Huisgen 1,3-dipolar cycloaddition between alkyne functionalized C(60) and azide functionalized polymer to give rise to shape amphiphiles with precisely defined surface chemistry and molecular topology. When 1,4-dioxane/DMF mixture was used as the common solvent and water as the selective solvent, these shape amphiphiles exhibited versatile self-assembled micellar morphologies which can be tuned by changing various parameters, such as molecular topology, polymer tail length, and initial molecular concentration, as revealed by transmission electron microscopy and light scattering experiments. In the low molecular concentration range of equal or less than 0.25 (wt) %, micellar morphology of the series of PS(n)-AC(60) studied was always spheres, while the series of 2PS(n)-AC(60) formed vesicles. Particularly, PS(44)-AC(60) and 2PS(23)-AC(60) are synthesized as a topological isomer pair of these shape amphiphiles. PS(44)-AC(60) formed spherical micelles while 2PS(23)-AC(60) generated bilayer vesicles under identical conditions. The difference in the self-assembly of PS(n)-AC(60) and 2PS(n)-AC(60) was understood by the molecular shape aspect ratio. The stretching ratio of PS tails decreased with increasing PS tail length in the spherical micelles of PS(n)-AC(60), indicating a micellar behavior that changes from small molecular surfactant-like to amphiphilic block copolymer-like. For the series of PS(n)-AC(60) in the high molecular concentration range [>0.25 (wt) %], their micellar morphological formation of spheres, cylinders, and vesicles was critically dependent upon both the initial molecular concentration and the PS tail length. On the other hand, the series of 2PS(n)-AC(60) remained in the state of bilayer vesicles in the same concentration range. Combining both of the experimental results obtained in the low and high molecular concentrations, a systematic morphological phase diagram was constructed for the series of PS(n)-AC(60) with different PS tail lengths. The versatile and concentration-sensitive phase behaviors of these molecular shape amphiphiles are unique and have not been systematically explored in the traditional surfactants and block copolymers systems.

The engineering of structures across different length scales is central to the design of novel materials with controlled macroscopic properties. Herein, we introduce a unique class of self-assembling materials, which are built upon shape-and volume-persistent molecular nanoparticles and other structural motifs, such as polymers, and can be viewed as a size-amplified version of the corresponding small-molecule counterparts. Among them, "giant surfactants" with precise molecular structures have been synthesized by "clicking" compact and polar molecular nanoparticles to flexible polymer tails of various composition and architecture at specific sites. Capturing the structural features of small-molecule surfactants but possessing much larger sizes, giant surfactants bridge the gap between small-molecule surfactants and block copolymers and demonstrate a duality of both materials in terms of their self-assembly behaviors. The controlled structural variations of these giant surfactants through precision synthesis further reveal that their selfassemblies are remarkably sensitive to primary chemical structures, leading to highly diverse, thermodynamically stable nanostructures with feature sizes around 10 nm or smaller in the bulk, thin-film, and solution states, as dictated by the collective physical interactions and geometric constraints. The results suggest that this class of materials provides a versatile platform for engineering nanostructures with sub-10-nm feature sizes. These findings are not only scientifically intriguing in understanding the chemical and physical principles of the self-assembly, but also technologically relevant, such as in nanopatterning technology and microelectronics. giant molecules | shape amphiphiles | hybrid materials | microphase separation | colloidal particles P hysical properties of materials are dictated by the hierarchical arrangements of atoms, molecules, and supramolecular assemblies across different length scales. The construction and engineering of structures at each length scale, especially at the 2-to 100-nm scale (1), are critically important in achieving desired macroscopic properties. As the traditional top-down lithography techniques face serious challenges in fabricating 2D and 3D nanostructured materials with sub-20-nm feature sizes (2), the bottom-up approach based on self-organization or directed assembly of functional molecules provides a promising alternative. The past decades have witnessed the development of diverse self-assembly building blocks ranging from small-molecule surfactants (3), block copolymers (4), and dendrimers (5) to DNAs (6, 7), peptides (8), and proteins (9). Notably, these motifs have enabled the programmed self-assembly of nanomaterials as demonstrated in DNA-coated nanoparticles (10-13). These studies have greatly improved our understanding of the thermodynamics and kinetics of self-assembly processes and opened enormous possibilities in modern nanotechnology.Noncovalent interactions, such as hydrogen bonding, amphiphilic effect, π-π interacti...