Photosensitizer ruthenium-based

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]. 

Fig. 6 Schematic representations of dendrimeric ruthenium based polypyridine photosensitizers...

Mixed artificial systems can also be created. A [NiFe] hydrogenase and a ruthenium-based photosensitizer have both been attached to the same Ti02 particles (Fig. 4c) [14]. By using... 

Figure 38.2 Structures of some representative ruthenium-based complexes used as photosensitizers N3 (a), N719 (b), and black dyes (N749) (c), respectively. TEA, tetrabutylammonium cation.

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 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 ... 

TOWARDS THE DESIGN OF MOLECULAR PHOTOCHEMICAL DEVICES BASED ON RUTHENIUM BIPYRIDINE PHOTOSENSITIZER UNITS. 

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],... 

Fig. 25. Comparison of the sunlight harvesting features of tris(2,2 -bipyridyl)ruthenium (9) and a copper-based multielectron transfer photosensitizer (138) carrying a 7i-acceptor ligand of the BIAN-type (13)...

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. 

Sano Y, Onoda A, Hayashi T (2012) Photocatalytic hydrogen evolution by a diiron hydrogenase model based on a peptide fragment of cytochrome C555 with an attached diiron carbonyl cluster and an attached ruthenium photosensitizer. J Inorg Biochem 108 159-162. doi 10.1016/j.jinorgbio.2011.07.010... 

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