On-Surface Synthesis and Characterization of a High-Spin Aza-[5]-Triangulene

Area of Science:

• Materials Science
• Surface Chemistry
• Quantum Chemistry

Background:

• Triangulenes are graphene flakes with spin increasing with size.
• On-surface synthesis allows precise fabrication of triangulenes.
• Direct experimental proof of spin increase with size is lacking.

Purpose of the Study:

• Synthesize and characterize a large nitrogen-doped triangulene (aza-[5]-triangulene).
• Detect the high-spin ground state of the synthesized molecule on a surface.
• Investigate the role of electron transfer and N-substitution on spin states.

Main Methods:

• Combined in-solution and on-surface synthesis.
• Atomic precision fabrication on Au(111) surface.
• Bond-resolved scanning tunneling microscopy (STM) and spectroscopy.
• Kondo screening analysis and theoretical simulations.

Main Results:

• Successful synthesis of aza-[5]-triangulene on Au(111).
• Detection of radical states along zigzag edges via STM.
• Observation of Kondo screening indicating a high-spin state.
• Experimental evidence for a quintet ground state (S=2), higher than expected.

Conclusions:

• Electron transfer to the Au(111) substrate increases the ground state spin.
• N-substitution modifies aromaticity and stabilizes charge on the surface.
• The study confirms a surface-induced high-spin state in aza-triangulene.