title: Photophysical and redox properties of dinuclear Ru and Os polypyridyl complexes with incorporated photostable spiropyran bridge.
abstract: Aimed at creating a true photoswitchable energy transfer system, four dinuclear complexes containing ruthenium(II) and osmium(II) metal centers bridged by spiropyran-type linkers were designed and investigated. The bridge in its closed spiropyran form was shown to be a good insulator for energy transfer between the Ru-bpy donor and the Os-bpy acceptor (bpy = 2,2'-bipyridine). On the basis of properties of previously reported photochromic nitrospiropyrans substituted with a single polypyridine metal center, conversion of the bridge to the open merocyanine form was envisaged to result in efficient electronic energy transfer by a sequential ("hopping") mechanism. In contrast to the expectations, however, the studied closed-form dinuclear complexes remained stable independently of their photochemical or electrochemical activation. This difference in reactivity is attributed to the replacement of the nitro group by a second polypyridine metal center. We assume that these changes have fundamentally altered the excited-state and redox properties of the complexes, making the ring-opening pathways unavailable.
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
authors.forename: Ron T F
authors.initials: RT
authors.lastname: Jukes
authors.forename: Biljana
authors.initials: B
authors.lastname: Bozic
authors.forename: Peter
authors.initials: P
authors.lastname: Belser
authors.forename: Luisa
authors.initials: L
authors.lastname: De Cola
authors.forename: Frantisek
authors.initials: F
authors.lastname: Hartl