Fig. 5

On-surface homocoupling of precursor 5c yields fully planar and neutral diaza-HBC 7c on Ag(111). a Scanning tunneling microscopy (STM) overview of reaction product and unreacted species on Ag(111). V _s = 30 mV, I _t = 10 pA. b Constant-height STM data of diaza-HBC with partially superposed molecular model. V _s = 5 mV. c Frequency-modulated atomic force microscopy (FM-AFM) and d Laplace-filtered FM-AFM data reveal details in the molecular structure. Apparent C = C distance 1.0 Å (black), and N–C 1.8 Å (blue). e FM-AFM simulations of 7c employing a neutral tip. Apparent C = C distance 1.5 Å (black), N–C 1.5 Å (blue). f FM-AFM simulations employing a negatively charged probe tip. Apparent C = C distance 1.3 Å (black), N-C 1.9 Å (blue). For simulation parameters see Methods. g–n Constant-height STM data (g, i, k, m) at different biases and corresponding (h, j, l, n) DFT simulations. White arrows point to N atoms oriented along the diaza-HBC symmetry axis. Scale bars (a) 20 Å, (b–f) 2 Å, (g–n) 5 Å