Electronic structures, photophysical properties, and electrochemistry of ruthenium(II)(bpy)2 pyridylimidazole complexes

✍ Scribed by Kyle M. Lancaster; James B. Gerken; Alec C. Durrell; Joshua H. Palmer; Harry B. Gray

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 962 KB
• Volume: 254
• Category: Article
• ISSN: 0010-8545
• DOI: 10.1016/j.ccr.2010.04.005

✦ Synopsis

The properties of Ru II complexes involving the imidazole moiety are discussed. Complexes [Ru(bpy) 2 (L)] 2+ [bpy = 2,2 -bipyridine, L = 2-(2 -pyridyl)imidazole (2-pimH) and 4-(2 -pyridyl)imidazole (4-pimH)] have been synthesized and fully characterized. Reduction potentials are 0.76 V vs. Fc + /Fc 0 for both complexes in acetonitrile solution, and the deprotonated complexes undergo irreversible electrochemical oxidation at 0.38 V vs. Fc + /Fc 0 . Density functional theory (DFT) calculations suggest that oxidation of the protonated complexes is primarily metal-based and that of the deprotonated complexes is ligand-centered. The pK a of the 4-pimH complex was found to be 9.7 ± 0.2; the pK a of the 2-pimH complex is 7.9 ± 0.2. Luminescence lifetimes (L = 4-pimH, 277 ns; 2-pimH, 224 ns; 4pim -, 40 ns; 2pim -, 34 ns in 5% methanol/water solution) combined with quantum yield data and acid-base behavior suggest that the non-coordinated imidazole nitrogen tunes deactivation pathways.