title: Reversing the thermal stability of a molecular switch on a gold surface: ring-opening reaction of nitrospiropyran.
abstract: The ring-opening/closing reaction between spiropyran (SP) and merocyanine (MC) is a prototypical thermally and optically induced reversible reaction. However, MC molecules in solution are thermodynamically unstable at room temperature and thus return to the parent closed form on short time scales. Here we report contrary behavior of a submonolayer of these molecules adsorbed on a Au(111) surface. At 300 K, a thermally induced ring-opening reaction takes place on the gold surface, converting the initial highly ordered SP islands into MC dimer chains. We have found that the thermally induced ring-opening reaction has an activation barrier similar to that in solution. However, on the metal surface, the MC structures turn out to be the most stable phase. On the basis of the experimentally determined molecular structure of each molecular phase, we ascribe the suppression of the back reaction to a stabilization of the planar MC form on the metal surface as a consequence of its conjugated structure and large electric dipole moment. The metal surface thus plays a crucial role in the ring-opening reaction and can be used to alter the stability of the two isomers.
authors.affiliation: Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Marten
authors.initials: M
authors.lastname: Piantek
authors.forename: Gunnar
authors.initials: G
authors.lastname: Schulze
authors.forename: Matthias
authors.initials: M
authors.lastname: Koch
authors.forename: Katharina J
authors.initials: KJ
authors.lastname: Franke
authors.forename: Felix
authors.initials: F
authors.lastname: Leyssner
authors.forename: Alex
authors.initials: A
authors.lastname: Krüger
authors.forename: Cristina
authors.initials: C
authors.lastname: Navío
authors.forename: Jorge
authors.initials: J
authors.lastname: Miguel
authors.forename: Matthias
authors.initials: M
authors.lastname: Bernien
authors.forename: Martin
authors.initials: M
authors.lastname: Wolf
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kuch
authors.forename: Petra
authors.initials: P
authors.lastname: Tegeder
authors.forename: José Ignacio
authors.initials: JI
authors.lastname: Pascual