Ruthenium complexes MLCT 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 ... 

This idea was realized in recent photoinduced deracemization of Co(acac)3 with A-[Ru(( —)-menbpy)3]2+ in the absence of oxygen [44]. When the solution of rac-Co(acac)3 and A-[Ru(( —)-menbpy)3]2+ was irradiated with visible light corresponding to the MLCT absorption of this ruthenium(II) complex, Co(acac)3 was little consumed, but the CD spectrum exhibited a positive peak at 580 nm and a negative one at 660 nm. This CD spectrum is the same as that of A-Co(acac)3. This result clearly shows that rac-Co(acac)3 converts to A-Co(acac)3 with A-[Ru(menbpy)3]2 +. ... 

Ruthenium and osmium polyazine complexes have been widely used as light absorbers. The complex [Ru(bpy)3] (Fig. 2) is a well studied LA with high extinction coefficients in the ultraviolet and visible regions of the spectrum. This complex shows intense absorptions in the UV region that are intraligand n- n (IL) and in the visible region that are MLCT transitions. Upon optical excitation at 450 nm, population of the Ru(d7i)- bpy(ji ) MLCT occurs. 

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