On-Surface Synthesis and Characterization of Tetraazanonacene

Area of Science:

• Organic Chemistry
• Materials Science
• Surface Science

Background:

• Isosteric replacement of carbon-hydrogen (CH) units in acenes with nitrogen significantly alters electronic, redox, and spectroscopic properties.
• Understanding the impact of nitrogen incorporation on extended aromatic systems is crucial for designing novel functional materials.

Purpose of the Study:

• To achieve on-surface synthesis of a nonacene analogue featuring four nitrogen atoms (tetraazanonacene).
• To investigate the electronic and aromatic properties of the synthesized tetraazanonacene.
• To compare the properties of tetraazanonacene with pristine nonacene and other nitrogen-substituted acenes.

Main Methods:

• On-surface synthesis using a two-step atom manipulation on a Au(111) surface.
• Characterization via scanning tunneling microscopy/spectroscopy (STM/STS) and noncontact atomic force microscopy (nc-AFM).
• Theoretical analysis using first-principles calculations.

Main Results:

• Successful synthesis of tetraazanonacene on the Au(111) surface.
• Nitrogen atoms lower frontier orbitals, increasing the scanning tunneling spectroscopy (STS) transport gap to 1.49 eV compared to nonacene.
• Pyridine-like ring formation in tetraazanonacene leads to stronger aromaticity modulation than pyrazine-like structures, differing from previous findings.

Conclusions:

• The study demonstrates a viable route for synthesizing extended azaacenes.
• Electronegative nitrogen atoms significantly tune the electronic properties and aromaticity of acene derivatives.
• The findings provide insights into structure-property relationships in nitrogen-containing polycyclic aromatic hydrocarbons.