Fig. 2: Scanning tunneling micrographs showing the evolution of conformation and assembly of pyrazinacene 2 with its progressive chemical conversion/oxidation on Cu(111) of 2 on Cu(111) substrate.

a Double-lobed shape of randomly distributed, individually adsorbed molecules of 2 observed after deposition onto the substrate held at room temperature (Image taken at 5 K: 50 × 50 nm, 10 pA, 1 V). b By thermal activation at ambient temperature, linear arrays form gradually within a few hours indicating a complex multi-step conversion process. This process is accelerated at elevated temperatures up to 150 °C. (Image: 50 × 50 nm, 30 pA, 500 mV). c Modified individual adsorbates observed after annealing at temperatures between 150 °C and 300 °C (Image: 50 × 50 nm, 10 pA, 1 V). The dark zone at the position of the molecular backbone and the reduced apparent height of the molecules (see also Fig. 3 and Supplementary Figs. 7 & 8) indicate their strengthened interaction with the substrate after annealing. d–f Magnified images of species shown in a–c, respectively. d The double-lobe shaped monomers are chiral as marked by an ‘S’ (Image: 4 × 4 nm, 50 pA, 1 V). e Line structures showing packed monomers (Note that the spots are identified as phenyl rings and the lines correspond to the acene backbone—see Fig. 3) (Image: 13 × 13 nm, 30 pA, 500 mV). f The characteristic modification of the individual molecules after annealing at higher temperature: this is reflected in a lower peak-peak corrugation in STM (see also STM profiles in Supplementary Figs. 7 & 8) and in the formation of low electron Density of States (DOS) regions at their center is consistent with dehydrogenation/cyclodehydrogenation (see main text and Fig. 3c, f) (Image: 4 × 4 nm, 30 pA, 500 mV). g–i N1s XP spectra of 2 on Cu(111): g as-deposited as in a, d; h after annealing at 150 °C as in b, c; i after annealing at 300 °C as in c, f. For the corresponding data for 1 see Supplementary Fig. 6.