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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...

Condensation reactions between the enantiopure, substitutionally inert building blocks Δ-[Ru(1,10-phenanthroline-5,6-dione)3][PF6]2 (2) and Δ-[Ru(phen)2(1,10-phenanthroline-5,6-diamine)][PF6]2 (3) gave the D 3-symmetric tetramer [(Δ-(phen)2Ru(tpphz))3-Δ-Ru]8+ (ΔΔ3-1) in 68% isolated yield as the PF6 - salt (where tpphz is tetrapyrido[3,2-a:2‘,3‘-c:3‘‘,2‘‘-h:2‘‘,3‘‘-j]phenazine). Reactions between appropriate enantiomers of 2 and 3 also yielded the remaining D 3 isomers ΛΔ3-1, ΔΛ3-1, and ΛΛ3-1 which collectively represent the highest nuclearity Ru oligomers based on bidentate type ligands prepared in a stereospecific fashion to give diasteromerically and enantiomerically pure products. The complexes were purified via cation-exchange HPLC. 1H and 13C NMR, COSY and HMQC NMR, and UV−visible spectroscopy were employed to characterize these supramolecular assemblies. MALDI-TOF mass spectrometry gave parent molecular ion peaks corresponding to the species m/z 2638 [1 − 8PF6]+, 2783 [1 − 7PF6]+, 2928 [1 − 6PF6]+, 3073 [1 − 5PF6]+, 3218 [1 − 4PF6]+, and 3363 [M − 3PF6]+, proving the macromolecular structure. Circular dichroism spectroscopy was used to determine the absolute stereochemistry and optical purity of each of these stereoisomers.

The stereospecific synthesis of three isomeric Ru dimers, Δ,Δ-[(phen)2Ru(tpphz)Ru(phen)2]4+ (Δ,Δ-4) (where tpphz = tetrapyrido[3,2-a:2‘,3‘-c:3‘‘,2‘‘-h:2‘‘,3‘‘-j]phenazine), Λ,Λ-4, and Λ,Δ-4, can be accomplished in high yield with retention of optical activity by the formation of a phenazine ring between appropriately functionalized chiral precursors.

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