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J. Am. Chem. Soc. 1999, 121, 1324-1336
Long-Lived Photoinduced Charge Separation and Redox-Type Photochromism on Mesoporous Oxide Films Sensitized by Molecular Dyads Pierre Bonhoˆ te,* Jacques-E. Moser, Robin Humphry-Baker, Nicolas Vlachopoulos, Shaik M. Zakeeruddin, Lorenz Walder,§ and Michael Gra1 tzel Contribution from the Laboratoire de Photonique et Interfaces, De´ partement de Chimie, Ecole Polytechnique Fe´ de´ rale de Lausanne, CH-1015 Lausanne, Switzerland ReceiVed May 19, 1998
Abstract: 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 1
2
photoinduced charge separation process follows the sequence D-S*|TiO2 f D-S+|(e-)TiO2 f 3
D+-S|(e-)TiO2 f 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 (
