Ruthenium complex absorption spectra

The long lifetimes and high redox potentials of a range of ruthenium(II) complexes and in particular [Ru(bpy)3] " have important consequences for their use as photoactive redox catalysts. This area of research is extremely active and we now focus on the decay of the excited state of [Ru(bpy)3] + ( [Ru(bpy)3] " ) and its quenching. Braterman et al. have described the electronic absorption spectrum and structure of the emitting state of [Ru(bpy3] +, and the effects of excited state asymmetry. The effects of solvent on the absorption spectrum of [Ru(bpy)3] " have been studied. In H2O, MeCN and mixtures of these solvents, the value of e(450 nm) remains the same ((4.6 0.4) x 10 dm mol cm ). The ground state spectrum is essentially independent of... 

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 ... 

Upon combination of complexes 1 and 2 in an equimolar 0.025 mM aqueous solution, the absorption spectrum displayed features of both complexes. On the contrary, the emission spectrum of such mixture showed a maximum centered at 645 nm, which resembled only one of the complex 1, while the emission of complex 2 was not detected. The time-resolved emission analysis confirmed that the decay was only related to complex 1 above the CMC. These findings strongly indicate a full and efficient energy transfer process involving the iridium-based metallosurfactant 2, being quenched by the ruthenium-based amphiphilic complex 1 in a system that can be depicted as a mixed aggregate. 

FRET, which converts color changes into luminescence information, either intensity or lifetime, based on the overlap of an inert luminescent donor and the absorption spectrum of an analyte-dependent acceptor. High levels of CO2 in a gas phase can be measured based on FRET between a ruthenium pol-ypyridyl complex and the pH indicator Sudan III. 

The dpp-bridged Ru(II)-Rh(III) complex displays typical absorptions for ruthenium and rhodium polyazine complexes in the UV and visible regions. The UV region in the electronic absorption spectrum of [(bpy)2Ru(dpp)Rh(bpy)2] in acetonitrile reveals two bands at = 312... 

The absorption spectra of tris-polypyridyl Rhodium(III) complexes are characterised by several intense Ligand Centered (LC) absorption bands in the UV. Neither MC absorption bands, nor CT bands are observed in the visible region of the spectrum in contrast to their Ruthenium analogues. This makes tris(polypyridyl)Rh(III) complexes formed with bpy and phen practically colorless [1]. 

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