Unexpected Rotamerism at the Origin of a Chessboard Supramolecular Assembly of Ruthenium Phthalocyanine

We have investigated the formation and the prop- erties of ultrathin films of ruthenium phthalocyanine (RuPc) 2 vacuum deposited on graphite by scanning tunneling mi- croscopy and synchrotron photoemission spectroscopy measurements, interpreted in close conjunction with ab initio simulations. Thanks to its unique dimeric structure connected by a direct Ru?Ru bond, (RuPc) 2 can be found in two stable rotameric forms separated by a low-energy barri- er. Such isomerism leads to a peculiar organization of the molecules in flat, horizontal layers on the graphite surface, characterized by a chessboard-like alternation of the two ro- tamers. Moreover, the molecules are vertically connected to form p-stacked columnar pillars of akin rotamers, compatible with the high conductivity measured in (RuPc) 2 powders. Such features yield an unprecedented supramolecular as- sembly of phthalocyanine films, which could open interest- ing perspectives toward the realization of new architectures of organic electronic devices.