Nonplanar adsorption and orientational ordering of porphyrin molecules on Au(111)

Saddle-shaped deformation of planar porphyrin molecules is accomplished by rotations of four phenyl-based substituents, which results from optimum adsorption onto Au(111) surface. The nonplanar macrocyclic conformation is clearly visualized by using low-temperature scanning tunneling microscopy and confirmed by molecular orbital calculations. Inside of the supramolecular molecular islands, we find that two different orientations of the nonplanar porphyrins are randomly distributed. An orientational ordering is obtained after short thermal excitations, which should be associated with steric intermolecular interactions between substituents. (C) 2001 American Institute of Physics.