Département de chimie moléculaire

A trinuclear [{\{}RuII(bpy)2(bpy-terpy){\}}2FeII]6+ complex (I) in which a FeII-bis-terpyridine-like center is covalently linked to two RuII-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 and compared with those of mononuclear model complexes. The cyclic voltammetry of (I) exhibits, in the pos. region, two successive reversible oxidn. processes, corresponding to the FeIII/FeII and RuIII/RuII redox couples. These systems are clearly sepd. ($Δ$E1/2 = 160 mV), demonstrating the lack of an electronic connection between the two subunits. The two oxidized forms of the complex, [{\{}RuII(bpy)2(bpy-terpy){\}}2FeIII]7+ and [{\{}RuIII(bpy)2(terpy-bpy){\}}2FeIII]9+, obtained after two successive exhaustive electrolyzes, are stable. The complex I is poorly luminescent, indicating that the covalent linkage of the RuII-tris-bipyridine to the FeII-bis-terpyridine subunit leads to a strong quenching of the RuII* excited state by energy transfer to the FeII center. Luminescence lifetime expts. show that the process occurs within 6 ns. The nature of the energy transfer process is discussed and an intramol. energy exchange is proposed as a preferable deactivation pathway. Nevertheless this energy transfer can be efficiently quenched by an electron transfer process in the presence of a large excess of the 4-bromophenyldiazonium cation, playing the role of a sacrificial oxidant. Finally complete photoinduced oxidn. of (I) has been performed by continuous photolysis expts. in the presence of a large excess of this sacrificial oxidant. The comparison with a mixt. of the corresponding mononuclear model complexes has been made. [on SciFinder(R)]