Ruthenium chromophores

Recently, a selective receptor for coppcr(ll) ion consisting of a ruthenium chromophore, lysine spacer and a cyclene unit was prepared (Scheme 3). [4]... 

The design of a dinuclear ruthenium chromophore, in which the mononuclear [Ru(bpy)3] + antenna molecule was replaced by a dinuclear ](bpy)2Ru(BL)Ru(bpy)2] complex (BL = 2,3-bis-(2-pyridyl)quinoxaline) led to a red-shift of the MLCT transition from 460 nm to 625 nm [311]. The luminescence quantum yield of the dinuclear dyad 16 gives rise to a very inefficient intramolecular... 

Triads containing two Ru(II)(terpy)2 end groups connected by one or two ethynyl spacers to a central Co(terpy)2 moiety have been described by Ziessel, Harriman, and co-workers [77]. Upon excitation of the ruthenium chromophore, excited-state electron transfer from the central cobalt site occurs, as shown by spectral identification of the transient species. The electron transfer thus occurs at a distance of 15 A. 

Comparisons of the spectroscopic and electrochemical properties of [(NH3)5RuNCFcCNRu(HN3)s] and [(NH3)5RuNCFcCNf where Fc is ferrocene, leads to the conclusions that the two ruthenium chromophores in the trimetallic ion do not interact strongly. This allows differences in the IT transition energies of the mixed-valence complexes to be ascribed to differences in charge distribution, in good agreement with theory. 

Meisel etal. [18-20] were the first to investigate how the addition of a polyelectrolyte affects photoinduced ET reactions. They found that charge separation was enhanced as a result of the retardation of the back ET when poly(vinyl sulfate) was added to an aqueous reaction system consisting of tris(2,2 -bipyridine)ruthenium(II) chloride (cationic photoactive chromophore) and neutral electron acceptors [21]. More recently, Sassoon and Rabani [22] observed that the addition of polybrene (a polycation) had a significant effect on separating the photoinduced ET products in an aqueous solution containing cir-dicyano-bis(2,2 -bipyridine)ruthenium(II) (photoactive donor) and potassium hexacyano-ferrate(III) (acceptor). These findings are ascribable to the electrostatic potential of the added polyelectrolytes. 

Tris(2,2 -bipyridine)ruthenium(II) complex (Ru(bpy)3+) has been most commonly employed as a chromophore in the studies of photoinduced ET. Electrostatic effects on the quenching of the emission from the Ru(II) complex covalently bound to polyeletrolytes have been studied by several groups [79-82]. 

ECL from inorganic chromophores has been observed from a variety of transition metal complexes of ruthenium, osmium, palladium, platinum, and a few other transition metal chromophores, some of which are listed in Tables 2 and 3. For example, ECL has been observed from tetrakis(pyrophosphito)diplatinate(II),... 

By introducing long alkyl side chains into the poly(p-phenylenevinylene) (PPV) backbones and to the amino groups on the NLO chromophores, a low-7), polymer X (Scheme 8) containing ruthenium complexes and a conjugated system is... 

A chromophore such as the quinone, ruthenium complex, C(,o. or viologen is covalently introduced at the terminal of the heme-propionate side chain(s) (94-97). For example, Hamachi et al. (98) appended Ru2+(bpy)3 (bpy = 2,2 -bipyridine) at one of the terminals of the heme-propionate (Fig. 26) and monitored the photoinduced electron transfer from the photoexcited ruthenium complex to the heme-iron in the protein. The reduction of the heme-iron was monitored by the formation of oxyferrous species under aerobic conditions, while the Ru(III) complex was reductively quenched by EDTA as a sacrificial reagent. In addition, when [Co(NH3)5Cl]2+ was added to the system instead of EDTA, the photoexcited ruthenium complex was oxidatively quenched by the cobalt complex, and then one electron is abstracted from the heme-iron(III) to reduce the ruthenium complex (99). As a result, the oxoferryl species was detected due to the deprotonation of the hydroxyiron(III)-porphyrin cation radical species. An extension of this work was the assembly of the Ru2+(bpy)3 complex with a catenane moiety including the cyclic bis(viologen)(100). In the supramolecular system, vectorial electron transfer was achieved with a long-lived charge separation species (f > 2 ms). 

The triad multistep electron transfer strategy is, of course, not limited to tetrapyrroles. For example, Meyer and coworkers have reported triad 19 [Ru(Me(bpy)-3DQ2+)(Me(bpy)-PTZ)2]4+, which is based upon a ruthenium trisbipyridyl chromophore [70, 71]. The Mebpy-PTZ and Mebpy-3DQ2+ ligands are shown as structures 20 and 21, respectively. This triad was again evidently... 

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