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

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.