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

• Published in: Inorganic chemistry Vol. 47; no. 12; pp. 5071 - 5078
• Main Authors: Easun, Timothy L, Alsindi, Wassim Z, Towrie, Michael, Ronayne, Kate L, Sun, Xue-Zhong, Ward, Michael D, George, Michael W
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16-06-2008
• Subjects: Energy transfer; Ethylene; Excitation spectra; Infrared spectroscopy; Ligands; Luminescence; Nanostructure; Spectroscopy
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic702005w

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 ReI-based triplet metal-to-ligand charge-transfer (3MLCT) luminescence and consequent sensitization of the RuII-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 ReI and amide carbonyl substituents on the bpy ligands coordinated to RuII] 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 ReI donor at different rates; and the presence of at least two conformers of the flexible molecule RuLRe, which have different Re···Ru separations.