Contents 1. Scope and Limitations 759 2. General Background 760 2.1. Localized Molecular Orbital Approximation 760 2.1.1. Classification of Excited States in Mononuclear Complexes 761 2.1.

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Decanuclear homoand heterometallic complexes of the general formula Mcj(BL)M;[(BL)Mp(L)2]2)320+ have been prepared as PF6" salts. The central (Mc), intermediate (Mj), and peripheral (M.) metal ions are Ru2+ or 0s2+, BL is the bridging ligand 2,3-bis(2-pyridyl)pyrazine (2,3-dpp), and L is either 2,2'-bipyridine (Spy) or 2,2'-biquinoline (biq). The decanuclear complexes have Seen synthesized by the reaction of appropriate building blocks, namely MC(BL)32+ cores, which contain three free chelating sites, with Mj[(BL)Mp(L)2]2Cl24+ species, which contain easily replaceable Cl" ligands. The six compounds prepared contain the following metals (M) and ligands (L) (BL is 2,3-dpp in all cases):

The new functionalized polypyridine ligands 4‘-(4-chlorophenyl)-6‘-phenyl-2,2‘-bipyridine (clpbpy), 4‘-(4-tolyl)-6‘-phenyl-2,2‘-bipyridine (tpbpy), and 4‘-(4-carboxyphenyl)-6‘-phenyl-2,2‘-bipyridine (cpbpy), together with the known 4‘-(4-hydroxyphenyl)-6‘-phenyl-2,2‘-bipyridine (hpbpy) and 4‘-(4-tolyl)-2,2‘:6‘,2‘ ‘-terpyridine (ttpy) have been used to prepare a new series of Ir(III) cyclometalated compounds [Ir(ppy)2(HL-X)][PF6] (ppy is the monoanion of 2-phenylpyridine; HL-X = hpbpy (1), clpbpy (2), tpbpy (3), cpbpy (4), and ttpy (5)). All the new species have been characterized by IR and 1H NMR, and the crystal structure of 4 is also presented and discussed. All the metal complexes exhibit oxidation mainly centered on an orbital derived from an Ir−(C-) σ-bond and ligand-centered reduction processes; all of them are luminescent from 3MLCT levels both at 77 K in a rigid matrix and at 298 K in fluid solution. The redox and absorption properties are more or less insensitive to the remote substituents on the rotationally free 4‘-phenyl ring, whereas fine-tuning of the luminescence properties is observed on changing substituents. The results show that the “energy gap law” for radiationless decay in the weak coupling limit is obeyed by this series of complexes, when complex 5 is excluded. Interestingly, the slope of the linear relationship between ln k nr and the emission energy at room temperature is significantly smoother than that reported for other luminescent polypyridine complexes containing different metals. Because of the high luminescence quantum yield and the presence of functionalities in the polypyridine ligand framework, the complexes reported may be considered as useful building blocks for light- and redox-active, multicomponent supramolecular systems.

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Two new ruthenium(II) polypyridyl dimers containing the large planar aromatic bridging ligands 9,11,20,22-tetraazatetrapyrido[3,2-a:2'3'-c:3' ',2''-l:2''',3'''-n]pentacene (tatpp) and 9,11,20,22-tetraazatetrapyrido[3,2-a:2'3'-c:3'',2' '-l:2''',3'''-n]pentacene-10,21-quinone (tatpq) have been synthesized and characterized by (1)H and (13)C NMR, MALDI mass spectrometry, and elemental analyses. The electronic properties (UV-vis, redox, photophysical) of these dimers are analyzed in the context of orbital calculations (PM3 level) on the bridging ligands. A localized orbital model is proposed in which low-lying acceptor orbitals on the center portion of the ligands effectively quench the Ru(II)-based MLCT emission via a mechanism that can be viewed as intramolecular electron transfer to specific subunits of the bridges.

Treelike (dendritic) structures made of Ru"-polypyridine complexes have been prepared by the "complexes-asmetals and complexes-as-ligands" synthetic strategy. The key building blocks are Ru" complexes of the 2,3-bis-(2-pyridy1)pyrazine (2.3-dpp) bridging ligand, where one of the two chelating sites can be protected by methylation. Dendendrimers exhibit strong absorption in the UV/Vis spectral region, a moderately strong red luminescence, and a great number of metal-based oxidation and ligandde de drimers containing four, ten, and twentytwo metal ions have been obtained. These SJISlreffts based reduction processes. The nature of the terminal ligands determines in which subunits of the supramolecular array the HOMO and LUMO orbitals and the luminescent excited state are localized. The reported synthetic strategy is eflicient, characterized by a full, step-by-step control of the growth process, and can be easily extended to building blocks containing other metals and/or ligands.

The absorption spectra, luminescence properties, and redox behavior of stereochemically pure, dendritic Ru(II) tetramers have been studied. Furthermore, the investigation has also been performed on stereochemically resolved dinuclear complexes of the same family and on racemic forms of their mononuclear precursors and models. The complexes studied are the racemic species [(phen)(2)Ru(1,10-phenanthroline-5,6-dione)](PF(6))(2) (A, phen = 1,10-phenanthroline), [(phen)(2)Ru(1,10-phenanthroline-5,6-diamine)](PF(6))(2) (B), [Ru(1,10-phenanthroline-5,6-dione)(3)](PF(6))(2) (C), [(phen)(2)Ru(tpphz)](PF(6))(2) (1, tpphz = tetrapyrido[3,2-a:2',3'-c:3' ',2' '-h:2' ',3' '-j]phenazine), [(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (2), and [{(phen)(2)Ru(&mgr;-tpphz)}(3)Ru](PF(6))(8) (4), the stereochemically pure dinuclear species DeltaDelta-[(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (DeltaDelta-2), LambdaLambda-[(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (LambdaLambda-2), and DeltaLambda-[(phen)(2)Ru(&mgr;-tpphz)Ru(phen)(2)](PF(6))(4) (DeltaLambda-2), and the stereochemically pure dendritic tetranuclear complexes [(Delta-(phen)(2)Ru(&mgr;-tpphz))(3)-Delta-Ru](PF(6))(8) (Delta(3)Delta-4), [(Delta-(phen)(2)Ru(&mgr;-tpphz))(3)-Lambda-Ru](PF(6))(8) (Delta(3)Lambda-4), and [(Lambda-(phen)(2)Ru(&mgr;-tpphz))(3)-Lambda-Ru](PF(6))(8) (Lambda(3)Lambda-4). All the complexes exhibit reversible metal-centered oxidation processes: the mononuclear complexes undergo a one-electron oxidation within the potential range +1.30 to +1.70 V vs SCE, whereas the dinuclear complexes undergo a two-electron oxidation at about +1.35 V and the tetranuclear compounds undergo a three-electron process at about +1.35 V followed by a one-electron process at +1.46 V. On reduction, each compound undergoes several reversible or quasireversible ligand-centered reductions within the potential window investigated (+2.00/-1.80 V vs SCE). The absorption spectra of the complexes exhibit intense ligand-centered (LC) bands in the UV region (epsilon up to 10(6) M(-)(1) cm(-)(1)) and moderately intense metal-to-ligand charge-transfer (MLCT) bands in the visible region (epsilon in the range 10(4)-10(5) M(-)(1) cm(-)(1)). All the complexes are luminescent both in fluid acetonitrile solution at room temperature (lambda(max) in the range 600-720 nm) and in MeOH/EtOH 4:1 (v/v) rigid matrix at 77 K (lambda(max) in the range 560-620 nm), except C which is luminescent only at 77 K. In all the cases, luminescence decays are monoexponential with lifetimes in the range 10(-)(5)-10(-)(8) s. Energy transfer occurs in the dendritic tetranuclear complexes from the central chromophore to the peripheral ones. For the oligonuclear tpphz-containing complexes, luminescence at room temperature and at 77 K originates from different MLCT states. When the experimental uncertainties are taken into account, the absorption spectra, luminescence properties, and redox behavior of the various stereoisomers studied here are practically undistinguishable one another. Comparison of our resul...