Département de chimie moléculaire

The trinuclear [{\{}RuII(bpy)2(bpy-terpy){\}}2CoII]6+ complex (16+) in which a Co(II)-bis-terpyridine-like center is covalently linked to two Ru(II)-tris-bipyridine-like moieties by a bridging bipyridine-terpyridine ligand has been synthesized and characterized. Its electrochem., photophys. and photochem. properties have been investigated in CH3CN. The cyclic voltammetry exhibits two successive reversible oxidn. processes, corresponding to the CoIII/CoII and RuIII/RuII redox couples at E 1/2 = -0.06 and 0.91 V vs Ag/Ag+ 10 mM, resp. The one-electron oxidized form of the complex, [{\{}RuII(bpy)2(bpy-terpy){\}}2CoIII]7+ (17+) obtained after exhaustive electrolysis carried out at 0.2 V is fully stable. 16+ and 17+ are only poorly luminescent, indicating that the covalent linkage of the Ru(II)-tris-bipyridine center to the cobalt subunit leads to a strong quenching of the RuII excited state by an intramol. process. Luminescence lifetime expts. carried out at different temps. indicate that the transfer is more efficient for 17+ compare to 16+ due to lower activation energy. Continuous irradn. of 17+ performed at 405 nm in the presence of P(Ph)3 acting as sacrificial electron donor leads to its quant. redn. into 16+, whereas similar expt. starting from 16+ with a sulfonium salt as sacrificial electron acceptor converts 16+ into 17+ with a slower rate and a max. yield of 80{%}. These photoinduced electron transfers were followed by UV-Visible spectroscopy and compared with those obtained with a simple mixt. of both mononuclear parent complexes i.e. [RuII(bpy)3]2+ and [CoII(tolyl-terpy)2]2+ or [CoIII(tolyl-terpy)2]3+ (tolyl-terpy = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine). [on SciFinder(R)]