D.E.) † Equally contributing authors. One Sentence Summary:The on-surface chemical reactions of molecular precursors on a pristine Au(111) surfaces results in the formation of long, defect-free, -conjugated polymers featuring a topological non-trivial SSH quantum phase, with a very narrow bandgap due to the proximity to the point of topological transition, in-gap zero-energy edge-states and electronic transformation of the π-conjugated polymers.

Resolution of the σ-hole Anisotropic distribution of charges on atoms plays an important role in intermolecular interactions, yet direct experimental imaging remains a long-standing challenge. A good example is the σ-hole, an anisotropic charge distribution on a halogen atom covalently linked to carbon atoms. The σ-hole gives rise to the halogen-bonding mechanism, which is well known in supramolecular chemistry despite its existence being confirmed only indirectly. Mallada et al . developed Kelvin probe force microscopy with a specifically functionalized tip and report direct real-space visualization of the σ-hole, revealing its strong anisotropic charge distribution. The authors show that this technique, which relies entirely on electrostatic interactions, may be a powerful tool with which to study anisotropic atomic charge distributions. —YS