Over the past ∼15 years our group has performed multiple structure/properties relationship studies to assess how logical structural refinement can affect the antiaromaticity/diradicaloid continuum. Us...

Stereochemistry, usually associated with the three-dimensional arrangement of atoms in molecules, is crucial in processes like life functions, drug action, or molecular reactions. This three-dimensionality typically originates from sp3 hybridization in organic molecules, but it is also present in out-of-plane sp2-based molecules as a consequence of helical structures, twisting processes, and/or the presence of nonbenzenoid rings, the latter significantly influencing their global stereochemistry and leading to the emergence of new exotic properties. In this sense, on-surface synthesis methodologies provide the perfect framework for the precise synthesis and characterization of organic systems at the atomic scale, allowing for the accurate assessment of the associated stereochemical effects. In this work, we demonstrate the importance of the initial diastereomeric configuration in the surface-induced skeletal rearrangement of a substituted cyclooctatetraene (COT) moiety–a historical landmark in the understanding of aromaticity–into a cyclopenta[c,d]azulene (CPA) one in a chevron-like graphene nanoribbon (GNR). These findings are evidenced by combining bond-resolved scanning tunneling microscopy with theoretical ab initio calculations. Interestingly, the major well-defined product, a CPA chevron-like GNR, exhibits the lowest bandgap reported to date for an all-carbon chevron-like GNR, as evidenced by scanning tunneling spectroscopy measurements. This work paves the way for the rational application of stereochemistry in the on-surface synthesis of novel graphene-based nanostructures.

Chiral nanographenes constitute an unconventional material class that deviates from planar graphene cutouts. They have gained considerable attention for their ability to exhibit circularly polarized luminescence (CPL), which offers new opportunities in chiral optoelectronics. Their unique π-conjugated architecture