Compounds polypyridine

Tetrathia- and tetraselenafulvalenes, polythiophenes and related compounds, polypyridines as organic electronic conductors 97YGK410. 

Dendrimers built around a metal complex as a core. These compounds can be considered metal complexes of ligands carrying dendritic substituents (Fig. 1 a). The most commonly used metal complex cores are porphyrin complexes, polypyridine complexes, and ferrocene-type compounds. 

Because of the presence of many polypyridine ligands, each capable of undergoing several reduction processes [38], the electrochemical reduction of this type of dendritic compound produces very complex electron exchange patterns. 

Compound 12 is the largest photoactive dendrimer in which organic branches have been attached around a polypyridine metal core [29]. This dendrimer was obtained by reacting the metal precursor with a modified bpy carrying highly-... 

Osawa et al. [ 112] described the Pd-catalyzed one-step graft reaction of metal-lodendron units with a core coordination (metal center=Ni, Cu, Ru) compound. This afforded a polypyridine-metal-based stiff dendritic architecture which... 

When only polypyridine-type ligands are present, each mononuclear metal-based unit exhibits intense LC bands in the UV region and moderately intense MLCT bands in the visible. As it is shown by the electrochemical behavior vide supra), in the polymetallic species there is some interaction among the neighboring metal-based units. To a first approximation, however, each building block carries its own absorption properties in the polynuclear species so that the molar absorption coefficients exhibited by the compounds of higher nuclearity are huge, as it is clear by a cursory examination of the absorption data reported in Table 3. For example, the spectra of the decanuclear compounds lOB and lOC (Scheme 1 and Table 1)... 

In the case of tetranuclear compounds belonging to the polypyridine family, all four possible energy migration patterns, schematized in Figure 21, have been obtained. Pattern (i) is found for L = bpy, BL = 2,3-dpp, and M = Ru. In such a complex, the three peripheral units are equivalent and Aeir lowest excited state lies at lower energy than the lowest excited state of the central unit.The reverse... 

Although the building blocks of the metal-polypyridine dendrimers are mononuclear species, the effective models for the high-nuclearity dendrimers are the dinuclear species. This is because the properties of the mononuclear and dinuclear compounds (absorption, luminescence, and redox properties) are significantly different, as a consequence of the bis-chelation of the dpp ligand.20-22 In the high-nuclearity dendrimers, dpp always plays the role of bridge, so the redox properties (and indeed also the spectroscopic properties) of the dendrimers are directly connected to the properties of the dinuclear species. Representative dinuclear species are discussed here. 

Rotaxane 316+ was specifically designed36 to achieve photoinduced ring shuttling in solution,37 but it also behaves as an electrochemically driven molecular shuttle. This compound has a modular structure its ring component is the electron donor macrocycle 2, whereas its dumbbell component is made of several covalently linked units. They are a Ru(II) polypyridine complex (P2+), ap-terpheny 1-type rigid spacer... 

Of course, there is no reason why the Ru-polypyridine complexes have to be the best photosensitizers. Studies should be performed on other families of transition metal compounds, with emphasis on complexes of inorganic ligands and on binuclear and polynuclear species. 

Durham BD, Pan LP, Hahm S, Long J, Millett F. Electron-transfer kinetics of singly labelled ruthenium(II) polypyridine cytochrome c derivatives. In Johnson MK, King RB, Kurtz DM, Kutal C, Norton ML, Scott RA (eds), Electron Transfer in Biology and the Solid States Inorganic compounds with unusual properties. ACS Advances in Chemistry Series. Washington DC American Chemical Society, 1990 180-93. 

Among the several species shown in Fig. 12, two special classes of compounds were systematically studied (31, 38, 39), consisting of tetrasubstituted pyridylpor-phyrins coordinated with four ruthenium-polypyridines (here denoted tetraruthe-nated pyridylporphyrin, TRPyP) or triangular ruthenium clusters (here denoted tetracluster pyridylporphyrin, TCPyP) (Fig. 13). 

A time resolution of approximately 10 ps is possible with the CFMIO method, although at such short times the mixing and chemical reaction take place simultaneously and the analysis becomes more complicated. Nonetheless, the method was used successfully in a study of the reactions of iron(III) and ruthenium(III) polypyridine complexes with several transition metal cyano compounds [3], but each experiment required approximately 300 mL of solution. The measured rate constants for electron transfer exceeded 3 x 10 M s . ... 

Currently, metal-polypyridine units are the molecular building blocks of choice whenever a compound with special electro- and/or photo-activity is to be designed. The research emphasis has somewhat shifted from fundamental studies of electron transfer reactivity and excited state properties of individual complexes to the design of new functional molecules and supermolecules with predetermined properties. 

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