Size-Increased All-Phenylene Molecular Spoked Wheels - A Combined Theoretical and Experimental Approach

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Molecular spoked wheels (MSWs) are complex molecular architectures with potential applications in nanotechnology.
• Previous attempts to synthesize large MSWs with all-phenylene backbones were hindered by aggregation and oligomerization issues.

Purpose of the Study:

• To develop a strategy for the lateral expansion of all-phenylene molecular spoked wheels.
• To overcome synthetic challenges associated with large, rigid molecular structures.

Main Methods:

• Synthesis of dodecabromo precursors for MSWs.
• Sixfold Yamamoto coupling for rim closure.
• Incorporation of fluorene units with alkyl chains into spokes.
• Quantum chemical calculations to understand reaction mechanisms.
• Characterization using spectroscopic methods and scanning tunneling microscopy (STM).

Main Results:

• Successfully synthesized larger MSWs with up to 30 phenylene rings in the perimeter.
• Demonstrated that fluorene units with alkyl chains prevent precursor aggregation and facilitate cyclization.
• Identified geometry and strain-related criteria for successful rim closure via quantum chemical calculations.
• Prepared MSWs with four and six phenylene units at each edge.

Conclusions:

• The incorporation of fluorene units is crucial for the successful synthesis of large, all-phenylene MSWs.
• Yamamoto coupling, guided by computational insights, is an effective method for constructing these complex architectures.
• The developed method allows for the controlled expansion of MSW size and complexity.