title: Structural and photophysical properties of adducts of [Ru(bipy)(CN)4]2- with different metal cations: metallochromism and its use in switching photoinduced energy transfer.
abstract: We show in this paper how the 3MLCT luminescence of [Ru(bipy)(CN)4]2-, which is known to be highly solvent-dependent, may be varied over a much wider range than can be achieved by solvent effects, by interaction of the externally directed cyanide ligands with additional metal cations both in the solid state and in solution. A series of crystallographic studies of [Ru(bipy)(CN)4]2- salts with different metal cations Mn+ (Li+, Na+, K+, mixed Li+/K+, Cs+, and Ba2+) shows how the cyanide/Mn+ interaction varies from the conventional "end-on" with the more Lewis-acidic cations (Li+, Ba2+) to the more unusual "side-on" interaction with the softer metal cations (K+, Cs+). The solid-state luminescence intensity and lifetime of these salts is highly dependent on the nature of the cation, with Cs+ affording the weakest luminescence and Ba2+ the strongest. A series of titrations of the more soluble derivative [Ru(tBu2bipy)(CN)4]2- in MeCN with a range of metal salts showed how the cyanide/Mn+ association results in a substantial blue-shift of the 1MLCT absorptions, and 3MLCT energies, intensities, and lifetimes, with the complex varying from essentially non-luminescent in the absence of metal cation to showing strong (phi = 0.07), long-lived (1.4 micros), and high-energy (583 nm) luminescence in the presence of Ba2+. This modulation of the 3MLCT energy, over a range of about 6000 cm-1 depending on the added cation, could be used to reverse the direction of photoinduced energy transfer in a dyad containing covalently linked [Ru(bipy)3]2+ and [Ru(bipy)(CN)4]2- termini. In the absence of a metal cation, the [Ru(bipy)(CN)4]2- terminus has the lower 3MLCT energy and thereby quenches the [Ru(bipy)3]2+-based luminescence; in the presence of Ba2+ ions, the 3MLCT energy of the [Ru(bipy)(CN)4]2- terminus is raised above that of the [Ru(bipy)3]2+ terminus, resulting in energy transfer to and sensitized emission from the latter.
authors.affiliation: Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom.
authors.forename: Theodore
authors.initials: T
authors.lastname: Lazarides
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Easun
authors.forename: Claire
authors.initials: C
authors.lastname: Veyne-Marti
authors.forename: Wassim Z
authors.initials: WZ
authors.lastname: Alsindi
authors.forename: Michael W
authors.initials: MW
authors.lastname: George
authors.forename: Nina
authors.initials: N
authors.lastname: Deppermann
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Hunter
authors.forename: Harry
authors.initials: H
authors.lastname: Adams
authors.forename: Michael D
authors.initials: MD
authors.lastname: Ward