Ruthenium polypyridyl

Nasr C, Hotchandani S, Kim WY, Schmehl RH, Kamat PV (1997) Photoelectrochemistry of composite semiconductor thin films. Photosensitization of Sn02/CdS coupled nanocrystal-Utes with a ruthenium polypyridyl complex. J Phys Chem B 101 7480-7487... 

Figure 8 Tuning of HOMO (t2g) and LUMO (tt ) orbital energy in various ruthenium polypyridyl...

The sensor for the measurement of high levels of CO2 in gas phase was developed, as well90. It was based on fluorescence resonance energy transfer between 0 long-lifetime ruthenium polypyridyl complex and the pH-active disazo dye Sudan III. The donor luminophore and the acceptor dye were both immobilized in a hydrophobic silica sol-gel/ethyl cellulose hybrid matrix. The sensor exhibited a fast and reversible response to carbon dioxide over a wide range of concentrations. 

With the aim of mimicking, on a basic level, the photoinduced electron-transfer process from WOC to P680+ in the reaction center of PSII, ruthenium polypyridyl complexes were used (182-187) as photosensitizers as shown in Fig. 19. These compounds are particularly suitable since their photophysical and photochemical properties are well known. For example, the reduction potential [Rum(bpy)3]3+/-[Run(bpy)3]2+ (bpy = 2,2 -bipyridine) of 1.26 V vs NHE is sufficiently positive to affect the oxidation of phenols (tyrosine). As traps for the photochemically mobilized electron, viologens or [Co(NH3)5C1]2+ were used. 

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]. 

Fig. 31. Connection of 5-(3"-aminopropynyl)-2 -deoxyuridine-5 -triphosphate to the succinimide active ester arm of a ruthenium polypyridyl complex.

To illustrate the tuning aspects of the MLCT transitions in ruthenium polypyridyl complexes, let us begin by considering the well-known ruthenium mT-bipyridine complex (1). Complex 1 shows strong visible band at 466 nm, due to charge-transfer transition from metal t2g (HOMO) orbitals to tt orbitals (LUMO) of the ligand. The Ru(II)/(III) oxidation potential is at 1.3 V, and the ligand-based reduction potential is at -1.5 V versus SCE [36]. From spectro chemical and electrochemical studies of polypyridyl complexes of ruthenium, it has been con-... 

The emission quantum yields are typically obtained by ratioing the areas under luminescence spectra for absorbance-matched samples of the species in question and a material of known quantum yield. This technique has been described in detail by Demas and Crosby [17] for ruthenium-polypyridyl systems. 

Figure 4.19 Examples of some typical electropolymerizable ruthenium polypyridyl complexes...

Figure 5.30 Molecular structure of the disulfide-linked ruthenium polypyridyl methyl viologen dyad, [RuC7VC6S]2 [65]...

Figure 5.50 Molecular structures of the disulfide-linked ruthenium polypyridyl methylviologen diads, [RuC VC6S]2, and ruthenium disulfide complexes, [RuCmS]2 (of variable chain lengths n and m, respectively), plus the structure of the electron acceptor 4ZV, reported by Yamada and co-workers [81]...

Excitation of the complexes leads to photoinduced electron transfer from the excited ruthenium polypyridyl site to the viologen acceptor. The Ru2+ site is restored through electron transfer from the TEOA or back-electron transfer from the bipyridine, while the viologen is oxidized by the electrode, thus generating the photocurrent. As illustrated in Figure 5.51, this mechanism is supported by experiments in which the electron acceptor 4ZV (see Figure 5.50) reduced the... 

Figure 6.11 Illustration of the photophysical processes expected for a TiCVbound ruthenium polypyridyl dye...

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 ... 

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. 

Photodissociation of 4-aminopyridine from ruthenium polypyridyl complex was reported recently [135], It was found that the complex does not interact with neurons, although the photoliberated ligand gives a strong physiological response. Photodissociation occurs at low-energy excitation. This research opens a new possibility for optical control of activity of selected groups of neurons for neurobio-chemical studies. 

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