Energy transfer intercomponent

Denti, G., Campagna, S., Serroni, S., Ciano, N., and Balzani, V. (1992) Decanuclear homo- and hetero-metallic polypyridine complexes Synthesis, absorption spectra, luminescence, electrochemical oxidation, and intercomponent energy transfer./. Am. Chem. Soc. 114, 2944-2950. 

As we have seen above (Section IV.C), in the polynuclear complexes dealt with in this review it is possible to identify components which can undergo photoexcitation independently from one another. The excited component can then give rise to intercomponent energy transfer processes, in competition with intracomponent decay. For most of the components which constitute the examined systems, the lifetime of the lowest excited state is long enough to allow the occurrence of energy transfer to nearby components when suitable energetic and electronic conditions are satisfied. This is not usually the case for upper excited states, which usually decay very rapidly (picosecond time scale) to the lowest excited state within each component. 

The dinuclear complex [(bpy)2Ru(bpt)Ir(ppy)2]2+ was reported by Haas-noot et al., Fig. 22b [ 124], In this complex the two metal centers are linked via a bpt bridging ligand containing a mono anionic triazole unit. Because of this electronic feature, the MLCT states localized on the two moieties involve the peripheral ligands and not the bridging ligand. In [(bpy)2Ru(bpt)Ir(ppy)2]2+, emission is only observed from the Ru-based unit and the direction of intercomponent energy transfer is Ir - Ru, i.e., in the opposite direction from that observed for [(bpy)2Ru(HAT)Ir(ppy)2]3+. 

It should be recalled, however, that even an interaction of a few cm (which cannot be noticed in spectroscopic experiments) may be sufficient to cause intercomponent energy transfer or electron transfer processes. As already mentioned, the nature and length of the bridging ligand can contribute strongly to the rate of the photoinduced processes. Many compounds have been labeled wire molecules, but in most cases the wire-type behavior could not be observed. However, one should first define what is a molecular wire and what are the expectations for such a system. 

The efficiency of long-distance energy transfer and its gradual decrease with intercomponent distance is usually described by an exponential decay law of the type Fab = F) exp (-yJtAe), where y is denoted the attenuation factor and 1 ab is the spatial separation between the redox sites. In the case of ligand-bridged complexes is set as the distance between the metal centres. 

In principle, such devices should take advantage of efficient intercomponent energy transfer from a number of "antenna chromophoric units to a specific chromophoric unit which behaves at the same time as an energy collector and as a charge injection sensitizer. In this way, the light... 

The second example to be discussed here belongs to a series of polychromophoric complexes synthesized in the context of some intercomponent energy transfer studies (see Section 5) [70]. These are cyano-bridged binuclear and trinuclear complexes of formula... 

The binuclear complexes discussed in this section further demonstrate, adding to what has been shown in section 4, how fast and efficient can intercomponent energy transfer across cyanide bridges be, even in the presence of very modest driving forces. Some of these studies provide examples of the great potential of time-resolved vibrational spectroscopy in the elucidation of detailed photophysical mechanisms. 

RU(II) AND/OR OS(II) TRIMETALLIC COMPLEXES OF TRIS(BIPYRIDINE) BRIDGING LIGANDS. ABSORPTION SPECTRA, LUMINESCENCE PROPERTIES, ELECTROCHEMICAL BEHAVIOR, AND INTERCOMPONENT ENERGY TRANSFER. 

Ru(II) and/or Os(II) trimetallic complexes of tris(bipyri-dine) bridging ligands. Absorption spectra, Iviminescence properties, electrochemical behavior, and intercomponent energy transfer... 

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