Aryl Radical Geometry Determines Nanographene Formation on Au(111)

Area of Science:

• Surface Chemistry
• Organic Synthesis
• Materials Science

Background:

• Ullmann coupling is a key method for C-C bond formation on surfaces.
• Aryl bromides and iodides are commonly used, limiting substrate scope.
• Graphene nanoribbon synthesis requires efficient surface coupling strategies.

Purpose of the Study:

• To investigate the use of aryl chlorides in surface-catalyzed Ullmann coupling.
• To explore the bottom-up assembly of graphene nanoribbons using aryl chlorides.
• To elucidate the reaction mechanism and intermediate structures.

Main Methods:

• Surface-catalyzed Ullmann coupling reactions on Au(111).
• Atomic resolution non-contact Atomic Force Microscopy (AFM) for structural analysis.
• Investigation of 10,10'-dichloro-9,9'-bianthryl (DCBA) reactivity.

Main Results:

• Aryl chlorides are viable precursors for Ullmann coupling on Au(111).
• Cyclodehydrogenation precedes dehalogenation and polymerization for aryl chlorides.
• Planar bisanthene radicals exhibit distinct coupling behavior from staggered bianthryl radicals.
• Formation of oligo- and polybisanthenes with fluoranthene-type linkages.

Conclusions:

• Aryl chlorides offer a new pathway for graphene nanoribbon synthesis via Ullmann coupling.
• Intermediate radical geometry critically dictates coupling mechanism and product formation.
• The study provides fundamental insights into surface-mediated polymerization.