Superlattice Engineering with Chemically Precise Molecular Building Blocks

Precisely Constructing Superlattices of Soft Giant Molecules via Regulating Volume Asymmetry

Soft matters, particularly giant molecular self-assembly, have successfully replicated complex structures previously exclusive to metal alloys. These superlattices are constructed from mesoatoms─supramolecular spherical motifs of aggregated molecules, and the formation of superlattices critically depends on the volume distributions of these mesoatoms. Herein, we introduce two general methods to control volume asymmetry (i.e., the volumes' ratio of the largest to smallest mesoatoms, VL/VS) within giant molecular self-assembly. Leveraging the spontaneous increase in the mesoatomic volume ratio in unary systems and self-sorted binary blends, we systematically adjust the volume asymmetry from 1.0 to 9.0 across 24 unary systems and 56 binary blends of giant molecules, uncovering the formation of various superlattices, including BCC, Frank-Kasper A15, σ, Laves C14, C15, NaZn13, AlB2, and notably, the first NaCl like superlattice in homogeneous soft matter self-assembly. A geometric-based analysis, combined with experimental results, further establishes a quantitative relationship between volume asymmetry and the corresponding superlattice formations, thus laying a solid foundation for superlattice engineering within giant molecular systems to mimic and even beyond metal alloys. The lattice parameters of various unit cells range from approximately 5 to 20 nm. Our investigation in giant molecules could guide the advancement of mesoscopic, periodic soft matter materials.

Self-assembled soft alloy with Frank-Kasper phases beyond metals

Soft building blocks, such as micelles, cells or soap bubbles, tend to adopt near-spherical geometry when densely packed together. As a result, their packing structures do not extend beyond those discovered in metallic glasses, quasicrystals and crystals. Here we report the emergence of two Frank-Kasper phases from the self-assembly of five-fold symmetric molecular pentagons. The μ phase, an important intermediate in superalloys, is indexed in soft matter, whereas the ϕ phase exhibits a structure distinct from known Frank-Kasper phases in metallic systems. We find a broad size and shape distribution of self-assembled mesoatoms formed by molecular pentagons while approaching equilibrium that contribute to the unique packing structures. This work provides insight into the manipulation of soft building blocks that deviate from the typical spherical geometry and opens avenues for the fabrication of 'soft alloy' structures that were previously unattainable in metal alloys.

A Thiol-Michael Approach Towards Versatile Functionalized Cyclic Titanium-Oxo Clusters

In expanding our research activities of superlattice engineering, designing new giant molecules is the necessary first step. One attempt is to use inorganic transition metal clusters as building blocks. Efficient functionalization of chemically precise transition metal clusters, however, remains a great challenge to material scientists. Herein, we report an efficient thiol-Michael addition approach for the modifications of cyclic titanium-oxo cluster (CTOC). Several advantages, including high efficiency, mild reaction condition, capability of complete addition, high atom economy, as well as high functional group tolerance were demonstrated. This approach can afford high yields of fully functionalized CTOCs, which provides a powerful platform for achieving versatile functionalization of precise transition metal clusters and further applications.

Leveraging Macromolecular Isomerism for Phase Complexity in Janus Nanograins

It remains intriguing whether macromolecular isomerism, along with competing molecular interactions, could be leveraged to create unconventional phase structures and generate considerable phase complexity in soft matter. Herein, we report the synthesis, assembly, and phase behaviors of a series of precisely defined regioisomeric Janus nanograins with distinct core symmetry. They are named B₂DB₂ where B stands for iso-butyl-functionalized polyhedral oligomeric silsesquioxanes (POSS) and D stands for dihydroxyl-functionalized POSS. While BPOSS prefers crystallization with a flat interface, DPOSS prefers to phase-separate from BPOSS. In solution, they form 2D crystals owing to strong BPOSS crystallization. In bulk, the subtle competition between crystallization and phase separation is strongly influenced by the core symmetry, leading to distinct phase structures and transition behaviors. The phase complexity was understood based on their symmetry, molecular packing, and free energy profiles. The results demonstrate that regioisomerism could indeed generate profound phase complexity.

Progress in the self-assembly of organic/inorganic polyhedral oligomeric silsesquioxane (POSS) hybrids

This Review describes recent progress in the self-assembly of organic/inorganic POSS hybrids derived from mono-, di-, and multi-functionalized POSS cages. We highlight the self-assembled structures and physical properties of giant surfactants and chain-end- and side-chain-type hybrids derived from mono-functionalized POSS cages; main-chain-type hybrids derived from di-functionalized POSS cages; and star-shaped hybrids derived from multi-functionalized POSS cages; with various polymeric attachments, including polystyrene, poly(methyl methacrylate), phenolic, PVPh, and polypeptides.