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.

Azaacenes are acene analogs containing nitrogen atoms in their carbon‐based molecular skeletons and are attracting significant attention because of their potential application in organic electronics. However, polyazaacenes have solubility and stability issues. In this study, we report a modular approach employing 8,11‐dihydro‐1,4 : 8,11‐diethanopentacene‐2,3,9,10(1H,4H)‐tetraone (1) as a key compound for π‐extension with commercially available materials to synthesize a series of polytetraazaacene thermal precursors. Exploiting this strategy, tetraazaheptacene, tetraazanonacene, and tetraazaundecacene precursors were successfully synthesized. Thermogravimetric analysis revealed that the tetraazanonacene precursor can be converted to its corresponding tetraazanonacene in a nitrogen atmosphere. To extend the applicability of this method, compound 1 was also used to synthesize the cyclazaacene precursor at 0.8 % yield. This approach provides a new perspective for exploring the synthesis of polyazaacene and cyclazaacene precursors by using a crucial key compound via dehydration condensation reactions.

The Front Cover shows the formation of polyazaacene and cyclazaacene precursors, which can be simply synthesized from a versatile key compound. The cover image was inspired by fairy tales with imaginative little fairies. With the magic ingredients, little fairies can create a flower and necklace for their elf, resembling the molecules in this article. More information can be found in the Research Article by H. Hayashi, H. Yamada et al.