title: Photoinduced energy transfer in a conformationally flexible Re(I)/Ru(II) dyad probed by time-resolved infrared spectroscopy: effects of conformation and spatial localization of excited states.
abstract: The dyad RuLRe contains (Re(bpy)(CO)3Cl) and (Ru(bpy)(bpyam)2)2+ termini (bpy = 2,2'-bipyridine; bpyam = 4,4'-diethylamido-2,2'-bipyridine) separated by a flexible ethylene spacer. Luminescence studies reveal the expected Re --> Ru photoinduced energy transfer, with partial quenching of Re(I)-based triplet metal-to-ligand charge-transfer (3MLCT) luminescence and consequent sensitization of the Ru(II)-based 3MLCT luminescence, which has a component with a grow-in lifetime of 0.76 (+/-0.2) ns. The presence of IR-active spectroscopic handles on both termini [CO ligands directly attached to Re(I) and amide carbonyl substituents on the bpy ligands coordinated to Ru(II)] allowed the excited-state dynamics to be studied by time-resolved IR (TRIR) spectroscopy in much more detail than allowed by luminescence methods. A combination of picosecond- and nanosecond-time-scale TRIR studies revealed the presence of at least three distinct Re --> Ru energy-transfer processes, with lifetimes of ca. 20 ps and 1 and 13 ns. This complex behavior occurs because of a combination of two different Ru-based 3MLCT states (Ru --> L and Ru --> bpyam), which are sensitized by energy transfer from the Re(I) donor at different rates; and the presence of at least two conformers of the flexible molecule RuLRe, which have different Re...Ru separations.
authors.affiliation: Department of Chemistry, University of Sheffield, Sheffield, UK.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Easun
authors.forename: Wassim Z
authors.initials: WZ
authors.lastname: Alsindi
authors.forename: Michael
authors.initials: M
authors.lastname: Towrie
authors.forename: Kate L
authors.initials: KL
authors.lastname: Ronayne
authors.forename: Xue-Zhong
authors.initials: XZ
authors.lastname: Sun
authors.forename: Michael D
authors.initials: MD
authors.lastname: Ward
authors.forename: Michael W
authors.initials: MW
authors.lastname: George