Hierarchical Self-Organization of AB Dendron-like Molecules into a Supramolecular Lattice Sequence

To understand the hierarchical self-organization behaviors of soft materials as well as their dependence on molecular geometry, a series of AB dendron-like molecules based on polyhedral oligomeric silsesquioxane (POSS) nanoparticles were designed and synthesized. The apex of these molecules is a hydrophilic POSS cage with 14 hydroxyl groups (denoted DPOSS). At its periphery, there are different numbers (n = 1-8) of hydrophobic POSS cages with seven isobutyl groups (denoted BPOSS), connected to the apical DPOSS via flexible dendron type linker(s). By varying the BPOSS number from one to seven, a supramolecular lattice formation sequence ranging from lamella (DPOSS-BPOSS), double gyroid (space group of Ia3̅d, DPOSS-BPOSS₂), hexagonal cylinder (plane group of P6mm, DPOSS-BPOSS₃), Frank-Kasper A15 (space group of Pm3̅n, DPOSS-BPOSS₄, DPOSS-BPOSS₅, and DPOSS-BPOSS₆), to Frank-Kasper sigma (space group of P4₂/mnm, DPOSS-BPOSS₇) phases can be observed. The nanostructure formations in this series of AB dendron-like molecules are mainly directed by the molecular geometric shapes. Furthermore, within each spherical motif, the spherical core consists hydrophilic DPOSS cages with flexible linkages, while the hydrophobic BPOSS cages form the relative rigid shell, and contact with neighbors to provide decreased interfaces among the spherical motifs for constructing final polyhedral motifs in these Frank-Kasper lattices. This study provides the design principle of molecules with specific geometric shapes and functional groups to achieve anticipated structures and macroscopic properties.