Ruthenium-based dyes

As reported before, and as widely demonstrated in the literature, the hydroxyl groups ensure anchorage to Ti02 nanoparticles, as in the case of the most popular ruthenium-based dyes [32, 33],... 

This is considerably different from the recombination reaction with, for example, typical ruthenium dyes. This slow re-reduction of the dyad is explained by the low redox potential of the osmium center, the value of 0.66 V (vs. SCE) observed, points to a small driving force for the redox process. This observation is important for the design of dyes for solar cell applications. Osmium compounds have very attractive absorption features, which cover a large part of the solar spectrum. However, their much less positive metal-based oxidation potentials will result in a less effective re-reduction of the dyes based on that metal and this will seriously affect the efficiency of solar cells. In addition, for many ruthenium-based dyes, the presence of low energy absorptions, desirable for spectral coverage, is often connected with low metal-based redox potentials. This intrinsically hinders the search for dyes which have a more complete coverage of the solar spectrum. Since electronic and electrochemical properties are very much related, a lowering of the LUMO-HOMO distance also leads to a less positive oxidation potential. 

The sensitization properties of porphyrin compounds have also been improved by introducing dendron groups to the cyano substituted meso-stilbene moieties (46, 47). The aggregation of porphyrin was efficiently suppressed by the bulky dendrons while the electron injection to the conduction band of TiC>2 was improved by the cyano groups. The overall energy transfer efficiency was promoted remarkably to 2.76% for a solid DSSC. This is an encouraging result for a porphyrin dye and it offers the potential for porphyrins as alternatives to ruthenium-based dyes in the DSSC [82]. 

Dare-Edwards M. P., Goodenough J. B., Hamnett A., Seddon K. R. and Wright R. D. (1980), Sensitization of semiconducting electrodes with ruthenium-based dyes , Faraday Discussions, 285-298. 

M. P. Dare-Edwards, J. B. Goodenough, A. Andrew, K. R. Seddon, and R. D. Wright, Sensitisation of semiconducting electrodes with ruthenium-based dyes, Faraday Discussions of the Chemical Sodety, vol. 70, 285 pages, 1981. 

Figure 3.15 Structures of the standard ruthenium-based dyes used in DSSCs...

Figure 11.14 shows the carrier dynamics monitored by TRTS for Ti02 films sensitized by N719 ruthenium based dyes. The THz signal exhibits biphasic electron transfer kinetics which is typically reported for Ti02 sensitized by ruthenium-based dyes. in,ns component has been attributed to in-... 

A direct visualization of the potential distribution in the DSSC film was achieved by dye desorption experiments [42]. The common ruthenium-based sensitizing dyes desorb from the Ti02 surface at potentials negative of a threshold (-----1.0... 

In the most commonly studied configuration of the DSSC, the electron conductor is a wide band gap, nanocrystalhne, metal oxide film. Colloidal titanium dioxide is most often used although other wide band gap metal oxides are candidates. The sensitizer is a transition metal-based (usually ruthenium), organic dye, with excited state free energy sufficient to reduce the semiconductor, and containing ligands, such as carboxylates or phosphonates, which facilitate bonding to the semiconductor... 

A. Fillinger, B. A. Parkinson, The adsorption behavior of a ruthenium-based sensitizing dye to nanocrystalline Ti02 - coverage effects on the external and internal sensitization quantum yields, J. Electrochem. Soc. 1999, 146(12), 4559-4564. 

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.

Later on, such S-layer-based sensing layers were also used in the development of optical biosensors (optodes), where the electrochemical transduction principle was replaced by an optical one [97] (Fig. 10c). In this approach an oxygen-sensitive fluorescent dye (ruthenium(II) complex) was immobilized on the S-layer in close proximity to the glucose oxidase-sensing layer [97]. The fluorescence of the Ru(II) complex is dynamically quenched by molecular oxygen. Thus, a decrease in the local oxygen pressure as a result of... 

Molecular engineering of ruthenium complexes that can act as panchromatic CT sensitizers for Ti02-based solar cells presents a challenging task as several requirements have to be fulfilled by the dye, which are very difficult to be met simultaneously. The lowest unoccupied molecular orbitals (LUMOs) and the highest occupied molecular orbitals (HOMOs) have to be maintained at levels where photo-induced electron transfer into the Ti02 conduction band and regeneration... 

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