Photoinduced Ultrafast Dynamics of Coumarin 343 Sensitized p-Type-Nanostructured NiO Films

Photoinduced electron transfer from the valence band of nanocryst. NiO, a p-type semiconductor, to an excited bound dye, Coumarin 343, and the subsequent recombination have been measured by femtosecond transient absorbance spectroscopy probing with white light. It was found that both processes are nonexponential. The photoinduced electron transfer from the semiconductor to the excited bound dye has an ultrafast component (∼200 fs), which is comparable to the time consts. measured for photoinduced electron injection in C343-TiO2 colloid solns. The process is very efficient and constitutes the main path of deactivation of the excited dye. Back electron transfer is also remarkably fast, with the main part of the recombination process happening with a time const. of ∼20 ps. Dye-sensitized nanostructured p-type semiconductors are attractive materials due to their potential use as photocathodes in dye-sensitized solar cells and solid electrolytes in solid-state dye-sensitized solar cells. To the authors knowledge, this is the first time that the photoinduced electron-transfer kinetics of a sensitized p-type semiconductor has been studied

Photoinduced electron transfer in ruthenium(II) trisbipyridine complexes connected to a naphthalenebisimide via an oligo(phenyleneethynylene) spacer

The preparation and the characterization of three new dyads composed of a ruthenium trisbipyridine complex linked to a naphthalene bisimide electron acceptor via a phenyleneethynylene spacer of different length (one or two units) are reported. The dyads also differ by the anchoring position of the spacer on the bipyridine, which is appended either at the 4-position or the 5-position. Cyclic voltammetry and the UV-Vis absorption spectroscopy suggested that the spacer linked at the 5-position ensures a longer pi-conjugation length but the electron transfer rates indicate a lower electronic coupling, than in 4-position. Photoinduced emission yields indicate a significant quenching of the MLCT excited-state of the ruthenium complex in these dyads. Except for the dyad linked in 5 position with one phenyleneethynylene unit, the transient absorption spectroscopy of all the other dyads evidences that the MLCT excited-state decays almost exclusively by electron transfer to form the charge-separated state Ru-III-NBI-. This state could not be observed, presumably because the subsequent recombination to the ground state was much faster than its formation. In the dyad linked in 5 position with only one phenyleneethynylene unit, at room temperature, the (MLCT)-M-3* state is in equilibrium with the (NBI)-N-3* state, and it also decays via electron transfer. The notable feature of these dyads is first the occurrence of a relatively long-range electron transfer reaction via a bis(phenylethynylene) linking unit anchored at the 5 position. Secondly, we show within these series of compounds that subtle variations in the structure of the dyads (length of the spacer and anchoring position on bipy) have a strong impact on the rates and in the mechanism of decay of the (MLCT)-M-3* state. The photophysical properties of the dyads can be explained in terms of energy proximity of different excited states and magnitude of the electronic coupling according to the anchoring position

Sensitized hole injection of phosphorus porphyrin into NiO: toward new photovoltaic devices

This paper describes the preparation and the characterization of a photovoltaic cell based on the sensitization of a wide band gap p-type semiconductor (NiO) with a phosphorus porphyrin. A photophysical study with femtosecond transient absorption spectroscopy showed that light excitation of the phosphorus porphyrin chemisorbed on NiO particles induces a very rapid interfacial hole injection into the valence band of NiO, occurring mainly on the 2-20 ps time scale. This is followed by a recombination in which ca. 80% of the ground-state reactants are regenerated within 1 ns. A photoelectrochemical device, prepared with a nanocrystalline NiO electrode coated with the phosphorus porphyrin, yields a cathodic photocurrent indicating that electrons indeed flow from the NiO electrode toward the solution. The low incident-to-photocurrent efficiency (IPCE) can be rationalized by the rapid back recombination reaction between the reduced sensitizer and the injected hole which prevents an efficient regeneration of the sensitizer ground state from the iodide/triiodide redox mediator. To the best of our knowledge, this work represents the first example of a photovoltaic cell in which a mechanism of hole photoinjection has been characterized.[on SciFinder (R)

Accumulative electron transfer: Multiple charge separation in artificial photosynthesis

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Cobalt Polypyridyl-Based Electrolytes for p-Type Dye-Sensitized Solar Cells

Polypyridyl Co complexes with different substituents were applied as redox mediators in p-type dye-sensitized solar cells (p-DSCs), consisting of mesoporous NiO sensitized with a perylenemonoimide-naphthalenediimide (PMI-NDI) dyad. The photocurrent and photovoltages of the devices were found to depend on the steric bulk of the redox species rather than their electrochem. potential. Bulky substituents were found to slow the detrimental charge recombination reactions between holes in the NiO semiconductor and the reduced form of the redox couple. The open-circuit potential (VOC) of each of the devices was superior to the equiv. PMI-NDI-sensitized p-DSCs contg. the triiodide/iodide redox couple

Data for 'Self-Assembled Liposomes Enhance Electron Transfer for Efficient Photocatalytic CO2 Reduction'

Main - contains UV-vis, electrochemistry, cryogenic TEM, photocatalysis, product quantification, time-resolved and steady-state emission spectroscopy, transient absorption spectroscopy, UV-vis-NIR and Resonance Raman spectroelectrochemistry and image data related to main text sorted by respective figure. SI Data - contains all synthesis details (including 1H and 13C NMR, MS, microanalysis, FT-IR), liposome preparation details, electrochemistry, cryogenic TEM, photocatalysis, ime-resolved and steady-state emission spectroscopy, transient absorption spectroscopy, UV-vis-NIR and Resonance Raman spectroelectrochemistry, DFT calculated Raman spectra and structures and image data related to the Supplementary Information sorted by respective figure