The photoinduced charge separation in three different assemblies composed of an electron donor D and a chromophore sensitizer S adsorbed on nanocrystalline TiO2 films (D-S\TiO2) was investigated. In all of the systems, the sensitizer was a ruthenium(II) bis-terpyridine complex anchored to the semiconductor surface by a phosphonate group. In two of the assemblies, the donor was a 4-(N,N-di-p-anisylamino) phenyl group linked to the 4＇ position of the terpyridine, either directly (dyad D1-S) or via a benzyl ether interlocking group (dyad D2-S). In the third system, the sensitizer and the donor (3-(4-(N,N-di-p-anisylamino)phenoxy)-propyl-1-phosphonate) were coadsorbed on the surface ((D3+S)\TiO2). Laser flash photolysis showed that the photoinduced charge separation process follows the sequence D-S*\TiO2 -->(1) D-S+\(e(-))TiO2 -->(2) D+-S\(e(-))TiO2 -->(3) D-S\TiO2 Resonance Raman spectroscopy indicates that in the excited assemblies D2-S*\TiO2 and (D3+S*)\TiO2, one electron is promoted from the metal center to the terpyridine ligand linked to the semiconductor, whereas in the system D1-S*\TiO2 the excited electron is located on the ligand linked to the donor. The quantum yield of charge separation (steps 1 and 2) was found to be close to unity for the two former assemblies but only 60% for the latter one. In all three cases, the electron injection was very fast (<1 ns), and the hole transfer to the donor was fast (10-20 ns). The half-lifetime of the charge separated state (step 3) was 3 mu s for (D3(+)+S)\(e-)TiO2, as in the model system S+\(e-)TiO2; it was 30 mu s in D1(+)-S\(e(-))TiO2 and 300 mu s in D2(+)-S\(e-)TiO2. Electrodes made of any of the surface-confined dyads on conducting glass display a strong redox-type photochromism. When a positive potential (+0.5 V vs NHE) is applied to the electrode, charge recombination (step 3) is blocked. As a result, the visible absorption spectrum of the electrode changes, due to the appearance: of the absorption feature of the oxidized donor (lambda(max) = 730 nm). Return to the reduced state is achieved by electron injection through the conduction band of the TiO2 under forward bias (-0.5 V). None of the assemblies D1-S\TiO2 and D2-S\TiO2 gave better photovoltaic performances than the model system S\TiO2. This was attributed in the first case to the low injection efficiency and, in the second case, to an additional short-circuiting pathway constituted by the charge percolation inside the molecular monolayer and to the underlying conducting glass, as previously observed with monolayers of the donor D3.