Role of Specific Intermolecular Interactions for the Arrangement of Ni(II)-5, 10, 15, 20-Tetraphenyltetrabenzoporphyrin on Cu(111)

We have studied the coverage-dependent adsorption behavior of Ni(II)-5,10,15,20-tetraphenyltetra-benzoporphyrin on Cu(111) by scanning tunneling microscopy (STM) at room temperature. At medium coverages, the molecules self-assemble into two-dimensional islands, due to mutual stabilization through intermolecular interactions. Altogether, three different supramolecular arrangements coexist at low-to-medium coverages. On the basis of high-resolution STM images and density functional theory calculations, models for the three arrangements and the corresponding intramolecular conformations of the individual molecules are proposed. The observed polymorphism is attributed to a complex interplay of specific T-type and pi-pi stacking interactions between the phenyl groups. For Ni(II)-meso-tetrakis (4-tert-butylphenyl) benzoporphyrin, in which the aromatic periphery is modified by the attachment of tert-butyl groups, only one supramolecular arrangement on Cu(111) is found. This difference highlights the fact that the choice of peripheral ligands of the porphyrin derivatives plays an important role in the fabrication and tailoring of functional molecular architectures.