Molecular ancillary components

Two basic types of components may be distinguished active components, that perform a given operation (accept, donate, transfer) on photons, electrons, ions, etc. structural components, that participate in the build-up of the supramolecular architecture and in the positioning of the active components, in particular through recognition processes in addition, ancillary components may be introduced to modify or perturb the properties of the other two types of components. A basic feature is that the components and the devices that they constitute should perform their function ) at the molecular and supramolecular levels as distinct from the bulk material. Incorporation of molecular devices into supramolecular architectures yields functional supermolecules or assemblies (such as layers, films, membranes, etc.). 

The radiation scattered from Raman active molecules thus has three components the central line at a frequency Vo due to Rayleigh scattering and two ancillary lines displaced to either side the Stokes (Vo + v) and the anti-Stokes (vg-v) lines (Figure 6.6). The magnitude of the shift and the peak intensity can be related to molecular vibrations using normal coordinate analysis and other mathematical tools discussed in Section 6.3. 

The systems described in this section make use of -Ru(bpy)j - units as molecular components, and of cyanide as both terminal and bridging ligand. A representative example of this type of supramolecular system is the trinuclear complex NC-Ru(bpy)j-CN-Ru(bpy)2-NC-Ru(bpy)j-CN, schematically represented in Fig 6 [16]. In complexes of this type, cyanide, besides being a convenient connector, provides a simple way to introduce excited-state energy differences between the (otherwise identical) -Ru(bpy)j components. In NC-Ru(bpy)j-CN-Ru(bpy)2 NC-Ru(bpy)2-CN, the bridging mode (N-bonded to the central metal, C-bonded to the terminal ones) is imposed by die synthetic route used. Because of the already noticed influence of the ancillary ligands on the energy of the MLCT states of Ru(II) polypyridine complexes, the excited state of the central unit is lower by ca. 1600 cm than those of the terminal ones. 

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