Spherical Supramolecular Structures Constructed via Chemically Symmetric Perylene Bisimides: Beyond Columnar Assembly

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Organic Electronics

Background:

• Discotic molecules, such as perylene bisimides (PBIs), typically self-assemble into columnar or lamellar structures.
• The π-conjugated scaffolds and rectangular perylene cores of PBIs inherently favor these conventional packing arrangements.
• Expanding the structural diversity of PBI assemblies is crucial for developing novel PBI-based materials with enhanced functionalities.

Purpose of the Study:

• To investigate and report unconventional spherical packing phases in perylene bisimides (PBIs).
• To explore a strategy for achieving spherical PBI assemblies, deviating from typical columnar structures.
• To understand the influence of peripheral functionalization on PBI self-assembly behavior.

Main Methods:

• Functionalization of the perylene core with multiple polyhedral oligomeric silsesquioxane (POSS) cages.
• Characterization of the resulting supramolecular structures using techniques to identify packing phases.
• Investigating phase transitions through controlled annealing temperature variations.

Main Results:

• Discovery and characterization of several unconventional spherical packing phases: A15, σ, dodecagonal quasicrystalline (DQC), and body-centered cubic (BCC).
• Demonstration that POSS cage functionalization induces spherical PBI assemblies by increasing peripheral steric hindrance.
• Observation of an unusual inverse phase transition sequence (BCC to σ) upon increasing annealing temperature.

Conclusions:

• Peripheral functionalization with bulky groups like POSS cages is an effective strategy to achieve unconventional spherical PBI assemblies.
• This approach holds potential for inducing spherical self-assembly in other discotic molecules.
• The observed inverse phase transition sequence highlights complex thermal behavior in these novel PBI structures.