Ruthenium polypyridyl complexes sensitizers

Platinized and sensitized (by ruthenium polypyridyl complexes) layered alkali-metal titanates, niobates, and titaniobates were used as photocatalysts for H2 and IJ production [91]. The use of reversed micelles as microreactors was reviewed in a feature article [92]. 

Durrant and co-workers have compared the electron injection and recombination processes of 28 or Zn-28 with that of N3 (a famous ruthenium polypyridyl complex with very high IPCE). Their experiments revealed that the electron injection and recombination kinetic for these three dyes on the surface of Ti02 are almost identical. The high IPCE for N3 dye probably originates from the electron transfer from the iodide redox couple to the dye cations. It is also possible that the lower efficiency of porphyrin sensitizers was caused by the annihilation of the excited states between the neighboring porphyrin molecules because of the closed proximity [70],... 

Both phthalocyanines and porhyrins are very promising sensitizers for wide band gap semiconductors. DSSCs fabricated from these kind of sensitizers present overall power conversion efficiency as high as 7%, which is still smaller than that achieved by the ruthenium polypyridyl complexes though, but higher than most of other dyes. The multiplicity on the molecular structure modification of these compounds provides a great potential for further promotion on their sensitization properties. The research in this field is still far from systematic and comprehensive and quantitatively much less than the researches on polypyridyl ruthenium complexes. But... 

Nasr, C. Hotchandani, S. Kamat, P. V. Photoelectrochemical behavior of composite semiconductor thin films and their sensitization with ruthenium polypyridyl complex. In Photoelectrochemistry, K. Rajeshwar, ed., The Electrochemical Society Pennington, NJ, 1997, in press. 

Nogueira, A.R, L.F.O. Furtado, A.L.B. Formiga, M. Nakamura, K. Araki, and H.E. Toma (2(X)4). Sensitization of T1O2 by supramolecules containing zinc porphyrins and ruthenium-polypyridyl complexes. Inorg. Chem. 43,396-398. 

G. Ramakrishna, A. D. Jose, D. Krishnakumar, A. Das, D. K. Palit, and H. N. Ghosh, 2005. Strongly coupled ruthenium-polypyridyl complexes for efficient electron injection in dye-sensitized semiconductor nanoparticles. J. Phys. Chem. B 109,15445-15453. 

Electronic properties of hydroquinone-containing ruthenium polypyridyl complexes Ruthenium polypyridyl complexes bound to hydroquinone/ quinone moieties are expected to yield information on the behaviour of hydroquinone-type compounds in biological processes. Furthermore, ruthenium(II)-hydroquinone complexes involving O and N bonds are likely to absorb well into the visible region and therefore have potential as dyes in sensitized solar cells. A recent example in the application of spectroelectrochemistry to the study of hydroquinone-containing ruthenium polypyridyl complexes is the oxidation of [Ru(bipy)2(HL )]+ (H2L0 = 1,4-dihy-droxy-2,3-bis(pyrazol-l-yl)benzene) (Figure 9). 

Cyclic voltammetry is an excellent tool to explore electrochemical reactions and to extract thermodynamic as well as kinetic information. Cyclic voltammetric data of complexes in solution show waves corresponding to successive oxidation and reduction processes. In the localized orbital approximation of ruthenium(II) polypyridyl complexes, these processes are viewed as MC and LC, respectively. Electrochemical and luminescence data are useful for calculating excited state redox potentials of sensitizers, an important piece of information from the point of view of determining whether charge injection into Ti02 is favorable. 

The ruthenium(II) polypyridyl complexes are also popular but the brightnesses do not exceed 15,000 and thermal quenching is rather significant. This property can be utilized to design temperature-sensitive probes providing that the dyes are effectively shielded from oxygen (e.g., in polyacrylonitrile beads). Despite often very high emission quantum yields the visible absorption of cyclometallated complexes of iridium(III) and platinum(II) is usually poor (e < 10,000 M-1cm-1), thus,... 

Many PSPs are composed of probe dyes, such as polycyclic aromatic hydrocarbons (e.g., pyrene) and coordination compounds (e.g., platinum por-phryins and ruthenium(II) polypyridyl complexes) immobilized in various gas permeable polymer films such as silicon polymer, organic glassy polymers (e.g., poly(methylmethacrylate), polystyrene), fluorinated polymers, or cellulose derivatives such as ethyl cellulose [9,10]. As probe molecules interact with polymer matrices directly, the properties of PSPs strongly depend on the properties of polymer matrices. The oxygen permeability of polymer matrix is an especially important factor for highly sensitive PSP. 

In the example discussed above, the heterotriad consists of a photosensitizer and an electron donor. In the following example, a ruthenium polypyridyl sensitizer is combined with an electron acceptor, in this case a rhodium(lll) polypyridyl center [15]. The structure of this dyad is shown in Figure 6.21 above. The absorption characteristics of the dyad are such that only the ruthenium moiety absorbs in the visible part of the spectrum. Irradiation of a solution containing this ruthenium complex with visible light results in selective excitation of the Ru(ll) center and in an emission with a A.max of 620 nm. This emission occurs from the ruthenium-polypyridyl-based triplet MLCT level, the lifetime of which is about 30 ns. This lifetime is very short when compared with the value of 700 ns obtained for the model compound [Ru(dcbpy)2dmbpy)], which does not contain a rhodium center. Detailed solution studies have shown that this rather short lifetime can be explained by fast oxidative quenching by the Rh center as shown in the following equation ... 

Kuciauskas D, Freund MS, Gray HB et al (2001) Electron transfer dynamics in nanocrystalline titanium dioxide solar cells sensitized with ruthenium or osmium polypyridyl complexes. J Phys Chem B 105 392-403... 

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