Exploration of pyrazine-embedded antiaromatic polycyclic hydrocarbons generated by solution and on-surface azomethine ylide homocoupling

Xiao-Ye Wang,Akimitsu Narita,Felix Hennersdorf,Klaus Müllen,Jan J Weigand,Jonas Björk,Yuanqin He,Alexander Riss,Raju Rajesh,Marcus Richter,Manuela Garnica,Carlos-Andres Palma,Reinhard Berger,Xinliang Feng,Willi Auwärter,Johannes V Barth

doi:10.1038/s41467-017-01934-1

Abstract

Nanographenes, namely polycyclic aromatic hydrocarbons (PAHs) with nanoscale dimensions (>1 nm), are atomically precise cutouts from graphene. They represent prime models to enhance the scope of chemical and physical properties of graphene through structural modulation and functionalization. Defined nitrogen doping in nanographenes is particularly attractive due to its potential for increasing the number of π-electrons, with the possibility of introducing localized antiaromatic ring elements. Herein we present azomethine ylide homocoupling as a strategy to afford internally nitrogen-doped, non-planar PAH in solution and planar nanographene on surfaces, with central pyrazine rings. Localized antiaromaticity of the central ring is indicated by optical absorption spectroscopy in conjunction with theoretical calculations. Our strategy opens up methods for chemically tailoring graphene and nanographenes, modified by antiaromatic dopants.

Highlights

Nanographenes, namely polycyclic aromatic hydrocarbons (PAHs) with nanoscale dimensions (>1 nm), are atomically precise cutouts from graphene
To develop nanographenes with strong antiaromatic ring dopants, we consider the possibility of incorporating a pyrazine structure inside the aromatic core, which employs two “graphitic” N atoms in the framework, providing additional π-electrons when compared to a benzene ring. 1,4-Disubstituted pyrazine entails intriguing chemistry, expressing 8π antiaromatic, 7π non-aromatic, or 6π aromatic properties, depending on its oxidation state
The structure was further characterized by 1H–13C heteronuclear single-quantum correlation (HSQC) and 1H–13C heteronuclear multiple-bond correlation (HMBC) spectroscopies

Summary

Introduction

Nanographenes, namely polycyclic aromatic hydrocarbons (PAHs) with nanoscale dimensions (>1 nm), are atomically precise cutouts from graphene. To develop nanographenes with strong antiaromatic ring dopants, we consider the possibility of incorporating a pyrazine structure inside the aromatic core, which employs two “graphitic” N atoms in the framework, providing additional π-electrons when compared to a benzene ring.

Results

Conclusion