Electronic decoupling of polyacenes from the underlying metal substrate by sp3 carbon atoms

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SEPTEMBER 15, 2020

Mohammed S. G. Mohammed, Luciano Colazzo, Roberto Robles, Ruth Dorel, Antonio M. Echavarren, Nicolás Lorente and Dimas G. de Oteyza
Communications Physics 3, 159 (2020)


In this work we demonstrated the decoupling of polyacenes from an underlying Ag(001) surface by exploiting the non-planarity of the organic backbone imposed by sp3-type functional groups. The non-planarity imposed by the sp3 carbon atoms drives an electronic decoupling from the underlying substrate that has been shown to be sufficient to establish a double tunneling barrier and stabilize a singly charged molecule holding a net spin S = 1/2. Importantly, although the experiments have been performed on hydrogenated heptacene molecules, this concept may be transposed to many other polyaromatic hydrocarbons of great scientific interest.


On-surface synthesis is becoming an increasingly popular approach to obtain new organic materials. In this context, metallic surfaces are the most commonly used substrates. However, their hybridization with the adsorbates often hinder a proper characterization of the molecule’s intrinsic electronic and magnetic properties. Here we report a route to electronically decouple molecules from their supporting substrates. In particular, we have used a Ag(001) substrate and hydrogenated heptacene molecules, in which the longest conjugated segment determining its frontier molecular orbitals amounts to five consecutive rings. The non-planarity that sp3 atoms impose on the carbon backbone results in electronically decoupled molecules, as demonstrated by scanning tunneling spectroscopy measurements. The charging resonances of the latter imply the presence of double tunneling barriers. We further explain the existing relation between the charging resonance energy and their contrast, as well as with the presence or absence of additional Kondo resonances.