Synthesis and characterization of a $\pi$-extended Clar's goblet

TL;DR

This paper reports the synthesis and detailed characterization of a pi-extended Clar's goblet, a non-Kekulé polybenzenoid hydrocarbon with potential applications in organic spintronics, using advanced microscopy and quantum chemistry methods.

Contribution

It introduces a novel synthetic route to a pi-extended Clar's goblet and provides comprehensive electronic property analysis through microscopy and theoretical calculations.

Findings

Successful synthesis of a pi-extended Clar's goblet molecule.

Characterization of electronic properties and many-body states.

Insights into the molecule's open-shell ground and excited states.

Abstract

Concealed non-Kekul\'e polybenzenoid hydrocarbons have no sublattice imbalance yet cannot be assigned a classical Kekul\'e structure, leading to an open-shell ground state with potential application in organic spintronics. They constitute an exceedingly small fraction of the total number of polybenzenoid hydrocarbons that can be constructed for a given number of benzenoid rings, and their synthesis remains challenging. The archetype of such a system is Clar's goblet (C$_{38}$H$_{18}$), a diradical proposed by Erich Clar in 1972 and recently synthesized on a Au(111) surface. Here, we report the synthesis of a pi-extended Clar's goblet (C$_{76}$H$_{26}$), a tetraradical concealed non-Kekul\'e polybenzenoid hydrocarbon, by a combined in-solution and on-surface synthetic approach. By means of low-temperature scanning tunneling microscopy and atomic force microscopy, we characterized individual molecules adsorbed on a Cu(111) surface. We provide insights into the electronic properties of this elusive molecule, including the many-body nature of its ground and excited states, by mean-field and multiconfigurational quantum chemistry calculations.