Abstract
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 π-electron correlation.
Highlights
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
We demonstrate that a designed precursor can be used to synthesize the pristine undecacene 4
In addition to the detailed chemical and structural properties unveiled via STM and non-contact atomic force microscopy (nc-AFM) measurements, we report on STS experiments to characterize the electronic structure of the synthesized compounds
Summary
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. These dI/dV maps show an excellent agreement with the DFT-calculated local density of states (LDOS) maps of the frontier orbitals (Fig. 3i, middle and right column) and allow to assign the NIR to LUMO and PIR to HOMO of 1.
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