Perturbations slight absorption

Because aH bonds within the polymethine chain of symmetrical PMDs are significantly equalized and change slightly on excitation, relatively smaH Stokes shifts (500 600 cm ) are observed in their spectra. In unsymmetrical PMDs, the essential bond alternation exists in the ground state. However, bond orders in the excited state are found to be insensitive to the symmetry perturbation. As a result, the deviations of fluorescence maxima, are much lower than those of absorption maxima, (3,10,56—58). The vinylene shifts of fluorescence maxima of unsymmetrical PMDs are practicaHy constant and equal to 100 nm (57). 

As shown in Fig. 7, the electronic spectrum of 2+ intercluster heterovalent trimeric complex 46b includes IC absorption envelopes characteristic of both [RU3O]0 and [Ru30]+ moieties, which are only slightly perturbed compared with those in the corresponding neutral (46a) and 3+ complexes (46). Three reversible redox waves occur at +0.89, —0.29, and —1.57V in the CV... 

So far, we have discussed the crystalline field acting on the ion A due to an octahedral environment of six B ligand ions. In many optically ion activated crystals, such as Ti +rAlaOj, the local symmetry of the active ion A is slightly distorted from the perfect octahedral symmetry Oh symmetry). This distortion can be considered as a perturbation of the main octahedral field. In general, this perturbation lifts the orbital degeneracy of the tag and eg levels and then produces additional structure in the tag eg absorption/emission bands. 

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