Photoelectrochemical behavior of multimetallic assemblies based on [Ru(bpy)3]2+-terpyridine building block: [Ru(II)–M–Ru(II)]n+ in solution and [Ru(II)–M]n+ dyad anchored on ITO (M=Co(III), Fe(II))
Résumé
One of the bipyridines of a [Ru(bpy)3]2+ core has been substituted at its 5 position by a terpyridine chelating unit through an ether bridge. The modification has only a minor influence on the photophysical and electrochemical properties of the Ru(II) ccomplex. This metallo-ligand (C1) is used to obtain two trimetallic structures [RuII_CoIII_RuII]7+ and [RuII_FeII_RuII]6+ in solution by complexation of the corresponding metallic ion to the terpyridine site. Under irradiation, an efficient intramolecular electron transfer process occurs in [RuII*_CoIII_RuII]7+ with a kinetic rate constant of 9×106 s-1 resulting in the formation of [RuIII_CoII_RuII]7+. In the presence of a sacrificial electron donor, continuous irradiation leads to the reduced species [RuII_CoII_RuII]6+. On the other hand, [RuII*_FeII_RuII]6+ follows a deactivation pathway through an energy transfer process with a rate constant of 2×108 s-1. This energy transfer is not total and can be short-circuited in the presence of an external electron acceptor to form the oxidized [RuII_FeIII_RuII]7+.
Based on these results in solution, C1 has been used in a stepwise approach to construct two photoelectrodes on ITO taking advantage of the strong self-assembling interaction between phosphonates with ITO surface and terpyridine ligands with first row transition metals. The luminescence lifetimes of the resulting dyads on surface are drastically lowered compared to the systems in solution. ITO/[CoIII_RuII]5+ behaves as a photoanode in presence of TEOA as sacrificial electron donor and ITO/[FeII_RuII]4+ as a photocathode in presence of ArN2+ as sacrificial electron acceptor. The photocurrent magnitude depends on the coverage value and increases linearly with the power of the irradiation light, proving the good photostability of these ITO-dyads modified surfaces. Association of both photoelectrodes in a photoelectrochemical cell would result in a gain of 0.8 V.