Metal complexes ruthenium tris

In another approach, implemented with nanofibers based on ionic transition metal complexes [ruthenium(II) tris(bipyridine)] embedded in PEO, inter-digitated electrodes are used instead of sandwich geometries. Fibers are deposited across the gap between electrodes, and injected carriers recombine yielding luminescence from a point source that has sub-wavelength dimensions ( 0.2 x 0.3 pm, Figure 5.11). ... 

Photochemical reduction systems (Figure 5.11) require efficient light harvesting, usually by a so-called dye or sensitizer, and efficient charge separation and energy utilization. Transition metal complexes, particularly tris(2,2 -bipyridine)ruthenium(ll), serve as sensitizers. The overall reaction carried out must be a useful one. That is, in addition to carbon dioxide reduction, the complementary oxidation process (which provides the electrons) should be a desirable one. Both reduction and oxidation processes generally require catalysis. For carbon dioxide reduction, a number of the catalysts used in electrochemical systems are also effective in photochemical systems, as outlined below. 

Fluorescent redox switches based on compounds with electron acceptors and fluorophores have been also reported. For instance, by making use of the quinone/ hydroquinone redox couple a redox-responsive fluorescence switch can be established with molecule 19 containing a ruthenium tris(bpy) (bpy = 2,2 -bipyridine) complex.29 Within molecule 19, the excited state of the ruthenium center, that is, the triplet metal-to-ligand charge transfer (MLCT) state, is effectively quenched by electron transfer to the quinone group. When the quinone is reduced to the hydroquinone either chemically or electrochemically, luminescence is emitted from the ruthenium center in molecule 19. Similarly, molecule 20, a ruthenium (II) complex withhydroquinone-functionalized 2,2 6, 2"-terpyridine (tpy) and (4 -phenylethynyl-2,2 6, 2"- terpyridine) as ligands, also works as a redox fluorescence switch.30... 

Some years later, at the beginning of the 1970s, first ECL system based on the luminescent transition metal complex tris(2,2 -bipyridine)ruthenium(II)-Ru (bipy)32 + -has been reported.11 It was shown that the excited state 3 Ru(bipy)32 + can be generated in aprotic media by annihilation of the reduced Ru(bipy)31 + and oxidized Ru(bipy)33 + ions. Due to many reasons (such as strong luminescence and ability to undergo reversible one-electron transfer reactions), Ru (bipy)32+ later has become the most thoroughly studied ECL active molecule. 

Electrochemical switching of the emission of a metal complex occurs in a system in which a luminescent (tris-bipyridine)ruthenium(ll) centre is linked to a quinone unit. Interconversion of the redox couple 124-125 allows the reversible switching... 

Jaquet L, Kelly JM, Kirsch-De Mesmaeker A (1995) Photoadduct between tris(1,4,5,8-tetraazaphena nthrene)ruthenium(ll) and guanosine monophosphate - a model for a new covalent binding of metal complexes to DNA. J Chem Soc Chem Commun 913-914 Jay-Gerin J-P, Ferradini C (2000) A new estimate of the OFI radical yield at early times in the radiolysis of liquid water. Chem Phys Lett 317 388-391... 

In the transition metal polypyridyl complex group, tris(4,7-diphenylphen-antroline) ruthenium(II) (Ru(dpp)2+) is widely used as a probe for a PSP. The luminescence lifetime of Ru(dpp)2+ is long compared with the other ruthe-nium(II) polypyridyl complexes [17]. The absorption and emission maxima of Ru(dpp)2+ are 457 and 610 nm, respectively. The luminescence lifetimes under nitrogen- and air-saturated conditions are ca. 4.0 and 2.0 ps, respec-... 

One such example involves a ruthenium tris(bipyridine) complex, illustrated in Fig. 4.24, in which the metal can accept energy from photons and transfer it to the bipyridine ligands. The process of metal to ligand charge transfer is a well known phenomenon in coordination chemistry and the experimental conditions needed to form the complexes are fairly well understood. Added complexity is encountered when the bipyridine units have been modified as in the work of Hammarstrom [47],... 

The first report regarding quenching of DNA-bound metal complexes was of enantiomeric ruthenium(II)tris-diammine complexes by racemic cobalt(III)tris-... 

Dyes such as erythrosin B [172], eosin [173-177], rose bengal [178,179], rhodamines [180-185], cresyl violet [186-191], thionine [192], chlorophyll a and b [193-198], chlorophyllin [197,199], anthracene-9-carboxylate [200,201], perylene [202,203] 8-hydroxyquinoline [204], porphyrins [205], phthalocyanines [206,207], transition metal cyanides [208,209], Ru(bpy)32+ and its analogs [83,170,210-218], cyanines [169,219-226], squaraines [55,227-230], and phe-nylfluorone [231] which have high extinction coefficients in the visible, are often employed to extend the photoresponse of the semiconductor in photoelectro-chemical systems. Visible light sensitization of platinized Ti02 photocatalyst by surface-coated polymers derivatized with ruthenium tris(bipyridyl) complex has also been attempted [232,233]. Because the singlet excited state of these dyes is short lived it becomes essential to adsorb them on the semiconductor surface with... 

Table I shows examples of the steady-state and time-resolved emission characteristics of [Ru(phen)2(dppz)]2+ upon binding to various DNAs. The time-resolved luminescence of DNA-bound Ru(II) is characterized by a biexponential decay, consistent with the presence of at least two binding modes for the complex (47, 48). Previous photophysical studies conducted with tris(phenanthroline)ruthenium(II) also showed biexponential decays in emission and led to the proposal of two non-covalent binding modes for the complex (i) a surface-bound mode in which the ancillary ligands of the metal complex rest against the minor groove of DNA and (ii) an intercalative stacking mode in which one of the ligands inserts partially between adjacent base pairs in the double helix (36, 37). In contrast, quenching studies using both cationic quenchers such as [Ru(NH3)6]3+ and anionic quenchers such as [Fe(CN)6]4 have indicated that for the dppz complex both binding modes...

Dyads and triads based on the photoactive, multibridging [Ru(bpz)3] (bpz = bipyrazine) complex directly bound to transition metal complexes were obtained by following the procedures previously reported for the generation of symmetric heptanuclear supermolecules (67-69). Such systems contain a tris(bpz)ruthenium (II) ion [RuJ attached to bis(bpy)chlororuthenium(II)/(III) [Rup], or penta-cyanoferrate(II)/(III) complexes via a bpz bridging ligand, as shown for the... 

Hence, the first clearcut evidence for the involvement of enol radical cations in ketone oxidation reactions was provided by Henry [109] and Littler [110,112]. From kinetic results and product studies it was concluded that in the oxidation of cyclohexanone using the outer-sphere one-electron oxidants, tris-substituted 2,2 -bipyridyl or 1,10-phenanthroline complexes of iron(III) and ruthenium(III) or sodium hexachloroiridate(IV) (IrCI), the cyclohexenol radical cation (65" ) is formed, which rapidly deprotonates to the a-carbonyl radical 66. An upper limit for the deuterium isotope effect in the oxidation step (k /kjy < 2) suggests that electron transfer from the enol to the metal complex occurs prior to the loss of the proton [109]. In the reaction with the ruthenium(III) salt, four main products were formed 2-hydroxycyclohexanone (67), cyclohexenone, cyclopen tanecarboxylic acid and 1,2-cyclohexanedione, whereas oxidation with IrCl afforded 2-chlorocyclohexanone in almost quantitative yield. Similarly, enol radical cations can be invoked in the oxidation reactions of aliphatic ketones with the substitution inert dodecatungstocobaltate(III), CoW,20 o complex [169]. Unfortunately, these results have never been linked to the general concept of inversion of stability order of enol/ketone systems (Sect. 2) and thus have never received wide attention. 

The contribution of pulse radiolysis to general chemistry is very significant, and this is exemplified by the following studies of transition metal complexes. The reduction of tris(2,2 -bipyridine)ruthenium(III) ion by the hydrated electron was the first example of this type of reaction to show clearly the formation of a product in an electronically excited state [80] ... 

Related molecular dyads have been constructed in which a metal complex, often ruthenium(II) tris(2,2 -bipyridine) or similar, functions as chromophore and an appended organic moiety acts as redox partner. Other systems " have been built from two separate metal complexes. Each of these systems shows selective intramolecular electron transfer under illumination. Rates of charge separation and recombination have been measured in each case and, on the basis of transient spectroscopic studies, the reaction mechanism has been elucidated. The results are of extreme importance for furthering our understanding of electron-transfer reactions and for developing effective molecular-scale electronic devices. The field is open and still highly active. 

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