title: A pre-organised truxene platform for phosphorescent [Ru(bpy)2] and [Os(bpy)2] metal centres: a clear-cut switch from Förster- to Dexter-type energy-transfer mechanism.
abstract: We report on the synthesis, optical properties and energy-transfer features of a series of transition-metal-containing complexes and dyads, based on a pre-organised truxene scaffold. In this series, the [Ru(bpy)(3)](2+) and [Os(bpy)(3)](2+) photoactive terminals are coupled to the bridging aromatic truxene core through rigid ethynyl linkers. The photoinduced energy-transfer processes taking place from the Ru- to the Os-based levels, and from the truxene bridging ligand to the terminal-metal chromophores are studied and the pathways and mechanisms are discussed. The photoinduced energy-transfer process observed in the dyad proceeds rapidly through: i) an efficient (1)L-->(1)Os direct energy transfer followed by intersystem crossing to (3)Os, and ii) a fast (1)L-->(1)Ru energy-transfer step and subsequent intersystem crossing to (3)Ru followed by a (3)Ru-->(3)Os energy-transfer process. The first (1)L-->(1)Os and (1)L-->(1)Ru steps are controlled by a dipole-dipole interaction (Förster mechanism), whereas the subsequent (3)Ru-->(3)Os step proceeds by means of a long-range (approximately 24 A) through-bond mediated Dexter mechanism, facilitated by the conjugation along the bpy-truxene-bpy molecular axis.
authors.affiliation: Laboratoire de Chimie Organique et Spectroscopies Avancées (LCOSA), Ecole de Chimie, Polymères, Matériaux (ECPM), Université de Strasbourg (UdS), 25 rue Becquerel, 67087 Strasbourg Cedex 02, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Diring
authors.forename: Raymond
authors.initials: R
authors.lastname: Ziessel
authors.forename: Francesco
authors.initials: F
authors.lastname: Barigelletti
authors.forename: Andrea
authors.initials: A
authors.lastname: Barbieri
authors.forename: Barbara
authors.initials: B
authors.lastname: Ventura