Supramolecular and Chiral Effects at the Titanyl Phthalocyanine/Ag(100) Hybrid Interface

Nonplanar titanyl phthalocyanine (TiOPc) molecules, characterized by a central, highly dipolar Ti-O group, can offer further degrees of freedom in tailoring the properties of hybrid organic-inorganic structures. Here, we combine scanning tunneling microscopy and low-energy electron diffraction measurements with ab initio density functional theory calculations to investigate the interaction of TiOPc molecules with the Ag(100) surface. Isolated molecules are adsorbed with the macrocycle parallel to the surface in two different configurations: with the O atom pointing outward (UP configuration) or with the O atom pointing toward the surface (DOWN configuration). A different interaction of UP and DOWN molecules with the surface can account for their different orientation on the surface as well as for the observation of marked chiral effects only for UP molecules. Self-assembled domains of randomly mixed UP and DOWN molecules form at the monolayer coverage, driven by a subtle interplay between the molecule-surface interaction, the intermolecular dipolar attraction, and the side interaction between adjacent molecules. Chiral patterns of isolated molecules, observed by STM, are transferred to these domains. Remarkably, theoretical calculations disclose an interfacial nature of such chiral properties. Finally, a metallic behavior observed for the monolayer disappears for TiOPc molecules in a second layer, which are electronically decoupled from the substrate.