Fig. 2. Chemical structure of the studied molecules (a) PC1 and (b) ZnPC1. Each of the two central metal Zn ions in ZnPC1 is replaced by two H atoms in PC1. In solution, R represents an acetate (Ac), as synthesized. After in situ deprotection on the gold wire, R is either a hydrogen (H) atom or gold (Au). Side and top views of ball-and-stick representations of calculated (c) compressed and (d) stretched states of PC1 in the gas phase with R = H. Note that compressed and stretched geometries in panels (c) and (d) are both energetic minima.