title: Bowl inversion of surface-adsorbed sumanene.
abstract: Bowl-shaped π-conjugated compounds offer the possibility to study curvature-dependent host-guest interactions and chemical reactivity in ideal model systems. For surface-adsorbed π bowls, however, only conformations with the bowl opening pointing away from the surface have been observed so far. Here we show for sumanene on Ag(111) that both bowl-up and bowl-down conformations can be stabilized. Analysis of the molecular layer as a function of coverage reveals an unprecedented structural phase transition involving a bowl inversion of one-third of the molecules. On the basis of scanning tunneling microscopy (STM) and complementary atomistic simulations, we develop a model that describes the observed phase transition in terms of a subtle interplay between inversion-dependent adsorption energies and intermolecular interactions. In addition, we explore the coexisting bowl-up and -down conformations with respect to host-guest binding of methane. STM reveals a clear energetic preference for methane binding to the concave face of sumanene.
authors.affiliation: nanotech@surfaces Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology , Überlandstrasse 129, 8600 Dübendorf, Switzerland.
authors.forename: Rached
authors.initials: R
authors.lastname: Jaafar
authors.forename: Carlo A
authors.initials: CA
authors.lastname: Pignedoli
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bussi
authors.forename: Kamel
authors.initials: K
authors.lastname: Aït-Mansour
authors.forename: Oliver
authors.initials: O
authors.lastname: Groening
authors.forename: Toru
authors.initials: T
authors.lastname: Amaya
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Hirao
authors.forename: Roman
authors.initials: R
authors.lastname: Fasel
authors.forename: Pascal
authors.initials: P
authors.lastname: Ruffieux