Thesis presented December 21, 2017

Abstract:
This thesis aims to investigate the possibility of using TiO₂ nanoparticles (NPs) as a platform to immobilize proximal coordination complexes that can interact with each other by photoinduced electron transfer. We have studied hybrid nanomaterials combining [Ru(bpy)₃]²⁺ (bpy = 2,2'-bipyridine) as a photosensitizer and [Cr(ttpy)₂]³⁺ or [Mn(ttpy)(CO)₃Br (ttpy = 4'-(p-tolyl)-2,2':6',2''-terpyridine) as electron acceptors. To immobilize the various complexes on the surface of TiO₂, a phosphonic acid functional group was introduced on one of the bipyridines of the [Ru(bpy)₃]²⁺ center and on the terpyridines of the [Cr(ttpy)₂]³⁺ complex. Under visible light, the TiO₂/RuII colloid undergoes a photo-induced charge transfer process leading to a long-lived charge separation state (e )TiO₂/RuIII, which makes it possible to be engaged in successive oxidation or reduction reactions. In particular, the visible irradiation of the TiO₂/RuII colloid in the presence of [Cr(ttpy)₂]³⁺ and triethanolamine (TEOA) as a sacrificial electron donor allows the two-electron reduction of [Cr(ttpy)₂]³⁺. Subsequently, the [Cr(ttpy)₂]³⁺ complex has been immobilized on the TiO₂/RuII NPs to form a RuII/TiO₂/CrIII assembly in which the photoinduced electron transfer processes were investigated. In order to propose a system for the photocatalytic reduction of CO₂, the [Mn(ttpy)(CO)₃Br] and [Ru(bpy)₃]²⁺ complexes were co-immobilized on TiO₂ NPs following a chemistry on surface approach to form a RuII/TiO₂/MnI triad. Under irradiation at 470 nm, this system exhibits excellent selectivity towards HCOOH as the only product of CO₂ photoreduction in DMF/TEOA solvent mixture, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH) as a sacrificial electron donor. Another hybrid system linking a [Ru(bpy)₃]²⁺ unit to two pyrrole functions and being immobilized on TiO₂ has also been synthesized and studied. Under visible light, the transient (e-)TiO₂/[Ru-pyr]³⁺ species induce the polymerization of pyrrole to form a TiO₂/poly(Ru-pyr) nanocomposite. The nanocomposite deposited on an electrode generates, in the presence of TEOA, a stable anodic photocurrent of more than 10 μA.cm^-2. All the results show that TiO₂ NPs can be used to associate different complexes in a close environment by limiting the interactions in the ground state but allow photoinduced electron transfer processes between them. Depending on the redox potentials of the different components, the electron transfer takes place either through the semiconducting NPs or on the surface.

Keywords:
TO₂ nanoparticles, Photoinduced electron transfer, CO₂ reduction, Photophysics, EPR spectroscopy, Photoelectrodes

Download this thesis.