Fig. 1: On-surface synthesis of covalently linked macrocycles.

a Schematic illustrating the synthetic pathway from precursor (left) to the 12-unit macrocycle (right) with a proposed intermediate (precursor 1′) with embedded pentagonal ring (middle). The as-formed benzenoid rings (dehydrogenative cyclization) and pentagonal rings (demethylation) are highlighted in orange and red, respectively. Hexagon and dodecagon illustrate the corresponding geometries of polymer rings synthesized from precursor 1 and precursor 1′ (internal angle between the coupling sites is highlighted in blue). b Overview STM image after annealing precursor 1 on Au(111) at 530 K, revealing individual 12-unit macrocycle (one of them is highlighted with a red arrow) coexisting with curved segments or half rings (highlighted with white arrows) and polymer chains (V = 1.0 V, I = 200 pA). c Plot of energy differences between total energy divided by number of units and the reference energy of 12-unit macrocycle (zoom-in plot of the region around the energy minimum (n = 12) is shown in Supplementary Fig. 4). Inset shows the three-dimensional STM image of one 12-unit macrocycle (V = −0.1 V, I = 200 pA). The scale bars in (b) and (c) are 3 and 1 nm, respectively.