On-surface route for producing planar nanographenes with azulene moieties

TL;DR

This paper presents a novel on-surface synthesis method for creating planar nanographenes with azulene units, using a unique cyclodehydrogenation reaction characterized by STM, resulting in large, insoluble aromatic structures with potential functional applications.

Contribution

It introduces a new cyclodehydrogenation process to incorporate azulene into nanographenes, expanding the diversity of on-surface synthesized aromatic carbon structures.

Findings

Successful synthesis of azulene-containing nanographenes on Au(111)

STM characterization reveals detailed reaction mechanisms

Discovery of pore states within the [18]annulene core

Abstract

Large aromatic carbon nanostructures are cornerstone materials due to their increasingly active role in functional devices, but their synthesis in solution encounters size and shape limitations. New on-surface strategies facilitate the synthesis of large and insoluble planar systems with atomic-scale precision. While dehydrogenation is usually the chemical zipping reaction building up large aromatic carbon structures, mostly benzenoid structures are being produced. Here, we report on a new cyclodehydrogenation reaction transforming a sterically stressed precursor with conjoined cove regions into planar carbon platform by incorporating azulene moieties in their interior. Submolecular resolution STM is used to characterize this exotic large polycyclic aromatic compound on Au(111) yielding unprecedented insight into a dehydrogenative intramolecular aryl-aryl coupling reaction. The resulting polycyclic aromatic carbon structure shows a [18]annulene core hosting peculiar pore states confined at the carbon cavity.