Département de chimie moléculaire

Herein we report the synthesis and electrochemical and photophysical behaviors of a nanocomposite TiO2/P-[Ru-pyr]2+, where [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) cores bearing two pyrrole substituents on distinct bipyridines and a phosphonic anchoring group on the third bipyridine are immobilized on TiO2 colloidal nanoparticles. Under visible light and in the presence of O2 as a sacrificial electron scavenger, TiO2/P-[Ru-pyr]2+ was converted into a suprastructure TiO2/P-oligo(Ru-pyr), where the [Ru(bpy)3]2+ cores were linked together through a pyrrole coupling reaction. The photoinduced charge separated state (e–)TiO2/RuII-pyr+ was revealed by electron paramagnetic resonance (EPR) spectroscopy ((e–)TiO2 signal). The oxidative coupling of pyrroles was ascertained by identifying the additional organic radical EPR signal with DFT calculations of pyrrole-derived oligomers, combined with X-ray photoelectron spectroscopy (XPS) results. TiO2/P-oligo(Ru-pyr) exhibited a higher rate of electron injection from [Ru(bpy)3]2+* to TiO2 than for colloidal nanoparticules without pyrrole denoted as TiO2/P-[Ru]2+. The composites were then electrophoretically deposited on a fluorine-doped tin oxide surface and tested as photoanodes. At a bias of 0.12 V vs Ag/Ag+ 0.01 M, FTO/TiO2/P-oligo(Ru-pyr) in the presence of tertiary amine as a sacrificial electron donor, displayed a current density double that of FTO/TiO2/P-[Ru]2+ under similar conditions. XPS confirmed the stability of [Ru(bpy)3]2+ cores after the photopolymerization process, but a partial desorption was observed after the electrophoretic deposition.