The interaction of organometallic molecules with metal surfaces affects their conformation and accordingly their functionality. Surprising conformational complexity is revealed in single Au-porphyrin molecules on Au(111) exhibiting a variety of different asymmetric conformers. A combination of low-temperature scanning tunneling microscopy and spectroscopy experiments with density functional theory calculations discloses different registries of the pyrroles with the substrate lattice (determined and quantified with atomic precision) that cause asymmetric sub-Å buckling of the macrocycle and, furthermore, a redshift of the frontier-orbital energy gap.

• Received 28 October 2010

DOI:https://doi.org/10.1103/PhysRevB.83.165416