Topology and peripheral functionality govern intramolecular π-π stacking, solid-state self-assembly and chiroptical...

Area of Science:

• Carbon materials science
• Supramolecular chemistry
• Organic electronics

Background:

• Controlling interlayer organization in nanographenes is crucial as stacking geometry dictates electronic, supramolecular, and chiroptical properties.
• Developing strategies for precise structural control in nanographenes remains a significant challenge.

Purpose of the Study:

• To report a topological design strategy for rigid bilayer nanographenes.
• To achieve extensive intramolecular π-π overlap and tunable chiroptical properties.

Main Methods:

• Synthesis of two covalently locked extended helicenes (1 and 2) using Sonogashira/Diels-Alder reactions followed by Scholl oxidation.
• Structural analysis to confirm highly ordered bilayer architectures.
• Comparison with topological isomer EP9H to establish topology-property relationships.

Main Results:

• Successful synthesis of rigid bilayer nanographenes with extensive intramolecular π-π overlap.
• Peripheral triflyloxy substitution in molecule 2 altered solid-state self-assembly and enhanced circularly polarized luminescence (CPL) brightness.
• Demonstrated a clear topology-property relationship, where functionalization of 2 enhanced molar absorptivity and chiroptical output compared to EP9H.

Conclusions:

• The reported topological design strategy enables precise control over nanographene structures.
• Functionalization of nanographenes offers a route to tune chiroptical properties and CPL brightness.
• This work provides fundamental insights into structure-property relationships in advanced carbon materials.