Ruthenium complexes photosensitizers

Most photosensitizers, however, are reasonably photostable compounds, and their optical properties have been studied in depth. In particular, there has been much interest in ruthenium-based photosensitizers such as [Ru(bpy)3]2+ and [Ru(phen)3]2+, due to their stability and absorption of visible light. Detailed information on their optical properties, including ground and excited state information in relation to photosensitization, has been reviewed by Creutz et al. [16]. Similarly, the photochemistry and photophysics of rhenium complexes, as discussed here, have been reviewed in detail by Kirgan et al. [7]. 

Besides ruthenium complexes, rhenium complexes were also used as the photosensitizers in photovoltaic cells. Bulk heterojunction photovoltaic cells fabricated from sublimable rhenium complexes exhibited a power conversion efficiency of 1.7%.75,76 The same rhenium complex moiety was incorporated into conjugated polymer chains such as polymer 16a c (Scheme 9). Fabrication of devices based on conjugated rhenium containing polymers 17a c and SPAN by the LbL deposition method was reported.77 The efficiencies of the devices are on the order of 10 4%. 

In this section, some ruthenium complex containing polymers incorporated with charge transport functionalities are presented. Being incorporated with both photosensitizing and charge transport units in the same polymer molecule, they are considered promising candidates for polymeric photovoltaic cells. However, the photovoltaic properties have not been reported so far. 

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 ... 

There are several photocatalysts mimicking hydrogenase activity that are not based on metalloporphyrin systems. Among them there are mixed-valence complexes of rhodium or iridium, [41] as well as complex systems encompassing photosensitizers (eg ruthenium complexes) attached to a catalytic bimetallic centre [43], The design of more sophisticated systems approaches that of photosynthetic processes [44],... 

Photochemical methods offer a convenient tool to study intra- and interprotein ET because of their time resolution and selectivity. Various mechanistic and design approaches based on photochemistry of metal complexes have been undertaken. Most of the studies on protein electron transfer processes have been done for hae-moproteins using among others ruthenium complex as a photosensitizer, modified haemoproteins in which haem iron is substituted by another metal (mainly Zn), and CO-bonded haem proteins [6,7],... 

Ruthenium complexes can be employed as photosensitizers in several ways ... 

E. G, Paillous N, Vicendo P. Mechanism of DNA damage photosensitized by trisbipyrazyl ruthenium complex. Unusual role of Cu/Zn superoxide dismutase. Photochem Photobiol 2000 72 583-9. 

Tris(bipyridyl) complexes of ruthenium Another photosensitizer system that has been extensively studied in zeolites is tris(2,2 -bipyridine)ruthenium(ll) [Ru(bpy)3 +],... 

Two celebrated early investigations of transmembrane oxidation-reduction were interpreted in terms of direct electron exchange between redox partners bound at the opposite vesicle interfaces. One involved apparent reduction of diheptylviologen [( 7)2 V +] in the inner aqueous phase of phosphatidylcholine liposomes by EDTA in the bulk phase that was mediated by membrane-bound amphiphilic Ru(bpy)3 + analogs the ruthenium complexes acted as photosensitizers and were presumed to function as electron relays by undergoing Ru(II)-Ru(III) electron exchange across the bilayer [105]. The other apparently involved direct electron transfer between photoexcited Ru(bpy)3 + and bound at the opposite interfaces of asym-... 

Kamat P. V., Bedja I., Hotchandani S. and Patterson L. K. (1996), Photosensitization of nanocrystalline semiconductor films—modulation of electron transfer between excited ruthenium complex and Sn02 Nanocrystallites with an externally applied bias , J. Phys. Chem. 100,4900 908. 

A group in Switzerland has developed a photovoltaic cell that can function as a window for a building.376 In one example, a ruthenium pyridine complex photosensitizer is attached to the titanium dioxide semiconductor by a phos-phonate. An iodine-based electrolyte (Kl3 dissolved in 50 50 ethylene carbonate/propylene carbonate) is between the panes. All the films are so thin that they are transparent. The efficiency is 10-11%. Variants on such cells have included fullerenes377 and polypyrrole.378 The use of solid electrolytes will avoid problems that might occur if a seal on a liquid electrolyte leaked. 

Other Semiconductor-Ruthenium Complex Systems. Taqui Khan et al. used a ruthenium(III)-EDTA-bipyridyl complex as a photosensitizer in a Pt-Ti02 semiconductor particulate system [109]. The Ti02 powder was loaded with platinum by the procedure of Erbs et al. [110]. Here 50 mg of the Pt-Ti02 powder was stirred in 10 mL of 0.001 M K[Ru(EDTA)(bipy)] 3 to deposit the ruthenium complex on the Ti02 surface. The 3-treated powder was separated by centrifugation and dried at room temperature. 

Dynamics in cellular systems are well adapted to study by photophysical methods. Related to solar energy conversion also is a report of photosensitized electron transport from ethylenediaminetetracetic acid or Fe to Fe(CN)g across a liquid membrane containing both a surface-active ruthenium complex and vitamin The incorporation of a surface-active nicotinamide chloride... 

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