Ruthenium complex emission spectra

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. 

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