Photoelectrochemistry with integrated photosensitizer-electron acceptor and Au-nanoparticle arrays

Photosensitizer/electron acceptor molecular cross-linked Au-nanoparticle arrays are assembled on indium-doped tin oxide (ITO) electrodes by a layer-by-layer deposition process. A Ru(II)-tris-(2, 2'-bipyridine)cyclobis(paraquat-p-phenylene) catenane (1) or Zn(II)-protoporphyrin IX-bis(N-methyl-N'-undecanoate-4,4'-bipyridinium) (2) are used as molecular cross-linkers for the generation of Au-nanoparticle (13 +/- 1 nm) arrays of a controlled number of layers. The Au-nanoparticle arrays are characterized by absorbance spectroscopy and by electrochemical means. The electrodes functionalized with 1- or 2-cross-linked Au-nanoparticle arrays are used in photoelectrochemical experiments. The resulting action spectra of the photocurrents follow the absorbance spectra of the respective chromophores. Mechanistic studies indicate that the photocurrents originate from intramolecular electron-transfer quenching of the photoexcited state of the photosensitizer by the electron acceptor units, leading to the formation of intermediate redox species. The oxidized photoproduct oxidizes the sacrificial electron donor, Na(2)EDTA, whereas the reduced bipyridinium radical cations transfer the electrons to the bulk electrode support.