On-surface synthesis and characterization of nitrogen-substituted undecacenes

Heteroatom substitution in larger acenes represents a fundamental step towards precise engineering of the remarkable electronic properties of the acene family. Here, the authors present an on-surface synthesis strategy and detailed characterization for three undecacene analogs substituted with four nitrogen atoms. Heteroatom substitution in acenes allows tailoring of their remarkable electronic properties, expected to include spin-polarization and magnetism for larger members of the acene family. Here, we present a strategy for the on-surface synthesis of three undecacene analogs substituted with four nitrogen atoms on an Au(111) substrate, by employing specifically designed diethano-bridged precursors. A similarly designed precursor is used to synthesize the pristine undecacene molecule. By comparing experimental features of scanning probe microscopy with ab initio simulations, we demonstrate that the ground state of the synthesized tetraazaundecacene has considerable open-shell character on Au(111). Additionally, we demonstrate that the electronegative nitrogen atoms induce a considerable shift in energy level alignment compared to the pristine undecacene, and that the introduction of hydro-aza groups causes local anti-aromaticity in the synthesized compounds. Our work provides access to the precise fabrication of nitrogen-substituted acenes and their analogs, potential building-blocks of organic electronics and spintronics, and a rich playground to explore pi-electron correlation.

Automated summary

A successful on-surface synthesis strategy was used to synthesize three undecacene analogs substituted with four nitrogen atoms, and their electronic properties and energy level alignment changes were studied in detail. These nitrogen-substituted acenes and their analogs could potentially be important building-blocks for organic electronics and spintronics.