Ultrafast, Light-Induced Electron Transfer in a Perylene Diimide Chromophore-Donor Assembly on TiO2

Surface-bound, perylenediimide (PDI)-based molecular assemblies have been synthesized on nanocrystalline TiO2 by reaction of a dianhydride with a surface-bound aniline and succinimide bonding. In a second step, the Fe(II) polypyridyl complex [Fe-II(tpy-PhNH2)(2)](2+) was added to the outside of the film, also by succinimide bonding. Ultrafast transient absorption measurements in 0.1 M HClO4 reveal that electron injection into TiO2 by (PDI)-P-1* does not occur, but rather leads to the ultrafast formation of the redox-separated pair PDI center dot+,PDI center dot-, which decays with complex kinetics (tau(1) = 0.8 ps, tau(2) = 15 ps, and tau(3) = 1500 ps). With the added Fe(II) polypyridyl complex, rapid (<25 ps) oxidation of Fe(II) by the PDI center dot+,PDI center dot- redox pair occurs to give Fe(III),PDI center dot- persisting for >400 mu s in the film environment.