Selective supramolecular fullerene-porphyrin interactions and switching in surface-confined C ₆₀-Ce(TPP) ₂ dyads

The control of organic molecules, supramolecular complexes and donor-acceptor systems at interfaces is a key issue in the development of novel hybrid architectures for regulation of charge-carrier transport pathways in nanoelectronics or organic photovoltaics. However, at present little is known regarding the intricate features of stacked molecular nanostructures stabilized by noncovalent interactions. Here we explore at the single molecule level the geometry and electronic properties of model donor-acceptor dyads stabilized by van der Waals interactions on a single crystal Ag(111) support. Our combined scanning tunneling microscopy/spectroscopy (STM/STS) and first-principles computational modeling study reveals site-selective positioning of C ₆₀ molecules on Ce(TPP) ₂ porphyrin double-decker arrays with the fullerene centered on the π-system of the top bowl-shaped tetrapyrrole macrocycle. Three specific orientations of the C ₆₀ cage in the van der Waals complex are identified that can be reversibly switched by STM manipulation protocols. Each configuration presents a distinct conductivity, which accounts for a tristable molecular switch and the tunability of the intradyad coupling. In addition, STS data evidence electronic decoupling of the hovering C ₆₀ units from the metal substrate, a prerequisite for photophysical applications.