Nanographene-Oxy Radical Stabilized by a Carbaporphyrin Framework

Area of Science:

• Organic Chemistry
• Materials Science
• Nanotechnology

Background:

• Stable organic radicals are of interest for their unique open-shell electronic properties.
• Preparation of hexa-peri-hexabenzocoronene (HBC)-based radicals is challenging due to the inherent stability of HBC structures.
• Nanographene hybrids offer a potential platform for stabilizing reactive radical species.

Purpose of the Study:

• To develop a method for synthesizing stable HBC-based organic radicals.
• To investigate the properties and stability of these novel radicals.
• To explore the potential of these radicals as ligands in metal complexes.

Main Methods:

• Synthesis of a carbaporphyrin-like dipyrromethene-fused nanographene hybrid (HBCP).
• Acetoxylation and hydrolysis to form an inner-hydroxy-substituted HBCP (HBCP-OH).
• Oxidation of HBCP-OH to yield the stable HBC-oxy radical (HBCP-O) using MnO2.
• Characterization using EPR, cyclic voltammetry, transient absorption, and DFT calculations.
• Complexation of HBCP-O with Cu(III) and Pd(II) ions.

Main Results:

• A stable, air- and moisture-tolerant HBC-oxy radical (HBCP-O) was successfully synthesized.
• HBCP-O exhibits clear organic π radical character confirmed by multiple spectroscopic and computational methods.
• The radical acts as a ligand, forming distinct Cu(III) (closed-shell) and Pd(II) (open-shell radical) complexes.
• The Pd(II) complex retains its open-shell radical character.

Conclusions:

• A novel and straightforward synthetic route to stable nanographene-based organic radicals has been established.
• The synthesized HBC-oxy radical is robust and amenable to further functionalization via metal coordination.
• This work expands the possibilities for creating advanced functional materials based on stable organic radicals and metal complexes.