On-surface light-induced generation of higher acenes and elucidation of their open-shell character

José I Urgel,Jan Wilhelm,Roman Fasel,Shantanu Mishra,Masataka Yamashita,Roland Widmer,Marco Di Giovannantonio,Nao Hieda,Hironobu Hayashi,Hiroko Yamada,Carlo A Pignedoli,Pascal Ruffieux

doi:10.1038/s41467-019-08650-y

Abstract

Acenes are an important class of polycyclic aromatic hydrocarbons which have recently gained exceptional attention due to their potential as functional organic semiconductors. Fundamentally, they are important systems to study the convergence of physico-chemical properties of all-carbon sp2-frameworks in the one-dimensional limit; and by virtue of having a zigzag edge topology they also provide a fertile playground to explore magnetism in graphenic nanostructures. The study of larger acenes is thus imperative from both a fundamental and applied perspective, but their synthesis via traditional solution-chemistry route is hindered by their poor solubility and high reactivity. Here, we demonstrate the on-surface formation of heptacene and nonacene, via visible-light-induced photo-dissociation of α-bisdiketone precursors on an Au(111) substrate under ultra-high vacuum conditions. Through combined scanning tunneling microscopy/spectroscopy and non-contact atomic force microscopy investigations, together with state-of-the-art first principles calculations, we provide insight into the chemical and electronic structure of these elusive compounds.

Highlights

Acenes are an important class of polycyclic aromatic hydrocarbons which have recently gained exceptional attention due to their potential as functional organic semiconductors
Since the first report of using the Strating-Zwanenburg reaction[25], synthesis of hexacene to undecacene has been successfully demonstrated, though the compounds needed to be stabilized in a polymethyl methacrylate (PMMA) matrix[26,27], argon matrix[28] and a polystyrene matrix[29], which kept them from decomposing for a few hours
The synthesis of heptacene and nonacene precursors was accomplished by modified schemes of previous reports[28,40]

Summary

Introduction

Acenes are an important class of polycyclic aromatic hydrocarbons which have recently gained exceptional attention due to their potential as functional organic semiconductors. Since the first report of using the Strating-Zwanenburg reaction[25], synthesis of hexacene to undecacene (with the exception of decacene) has been successfully demonstrated, though the compounds needed to be stabilized in a PMMA matrix (hexacene and heptacene)[26,27], argon matrix (octacene and nonacene)[28] and a polystyrene matrix (undecacene)[29], which kept them from decomposing for a few hours In view of these limitations, conventional solution synthesis has been extended to single-crystal surfaces under ultra-high vacuum (UHV) conditions, which provide a versatile route toward the formation of stable molecules. In combination with complimentary theoretical calculations, this allows us to rationalize the nature of the ground state of larger acenes (i.e. open- or closed-shell)

Methods

Results

Conclusion