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)2vacuum deposited on graphite by scanning tunneling mi-croscopy and synchrotron photoemission spectroscopymeasurements, interpreted in close conjunction with abinitio simulations. Thanks to its unique dimeric structureconnected by a direct Ru?Ru bond, (RuPc)2can be found intwo stable rotameric forms separated by a low-energy barri-er. Such isomerism leads to a peculiar organization of themolecules 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 toform p-stacked columnar pillars of akin rotamers, compatiblewith the high conductivity measured in (RuPc)2powders.Such features yield an unprecedented supramolecular as-sembly of phthalocyanine films, which could open interest-ing perspectives toward the realization of new architecturesof organic electronic devices.