Edge-On Self-Assembly of Tetra-bromoanthracenyl-porphyrin on Silver Surfaces

Molecular self-assembly on surfaces is driven by the range of interactions between the molecules themselves and the substrate. Generally, a face-on structure is favored for aromatic molecules lying flat on the surface. Here we report on the supramolecular self-assembly of 5,10,15,20-tetrakis(10-bromoanthracen-9-yl)porphyrin on the Ag(111) and Ag(110) surfaces. Well-ordered molecular chains were observed by room-temperature scanning tunneling microscopy on both surfaces. The relatively small size of the unit cell revealed an edge-on configuration of the porphyrin macrocycles, i.e. perpendicular to the surface plane, as confirmed by molecular mechanics calculations. Distinct intermolecular interactions were found on the two surfaces, providing different molecular chain orientations on Ag(111) and on Ag(110).