title: Switching ability of nitro-spiropyran on Au(111): electronic structure changes as a sensitive probe during a ring-opening reaction.
abstract: Spiropyran is a prototype molecular switch which undergoes a reversible ring-opening reaction by photoinduced cleavage of a C-O bond in the spiropyran (SP) to the merocyanine (MC) isomer. While the electronic states and switching behavior are well characterized in solution, adsorption on metal surfaces crucially affects these properties. Using two-photon photoemission and scanning tunneling spectroscopy, we resolve the molecular energy levels on a Au(111) surface of both isomeric forms. Illumination at various wavelengths does not yield any observable switching rate, thus evidencing a very small upper limit of the quantum efficiency. Electron-induced switching from the SP to the MC isomer via generation of a negative ion resonance can be detected with a quantum yield of (2.2 ± 0.2) × 10(-10) events/electron in tunneling spectroscopy. In contrast, the back reaction could not be observed. This study reveals that the switching properties of surface-bound molecular switches can be very different compared with free molecules, reflecting the strong influence of the interaction with the metal substrate.
authors.affiliation: Freie Universität Berlin, Fachbereich Physik, Berlin, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Bronner
authors.forename: Gunnar
authors.initials: G
authors.lastname: Schulze
authors.forename: Katharina J
authors.initials: KJ
authors.lastname: Franke
authors.forename: José Ignacio
authors.initials: JI
authors.lastname: Pascual
authors.forename: Petra
authors.initials: P
authors.lastname: Tegeder