Ruthenium bipy complexes, quenching

The eel arises from the reaction of the radical anion C02 with [Ru(bipy)3]3+. It was noted that some quenching of [Ru(bipy)3] 2+ by the ruthenium(III) complex was possible. 

It has been remarked that in many respects, the chemistry of the luminescent excited state of tris-(2,2 -bipyridyl)ruthenium(ii)... is as well characterized as that of many ground-state metal complexes . Certainly kinetic data on the electron-transfer reactions of [Ru(bipy)3] +, both as oxidant and as reductant, are becoming plentiful year by year. These, and data for other excited metal ions, are listed in Table 6 (p. 58). Emission quenching of a series of polypyridyl-type ruthenium(ii) complexes with Cu + proceeds by electron transfer,... 

A new probe of solvent accessibility of bound sensitizers has been described and tested for the particular case of a series of Ru" and Os photosensitizers bound to sodium lauryl sulphate micelles. The method depends upon the large solvent deuterium effect on excited-state lifetimes, and a correlation has been established between accessibility of bound complexes and hydrophobicity of the ligands. Luminescence properties of amphiphilic annelide-type complexes of ruthenium in micellar phases have been described. In the case of [4,4 -bis(nonadecyl)-2,2 -bipyridyl]bis-[4,4 -di-(10,13,16-trioxaundecyl)-2,2 -bipyridyl]ruthenium dichloride, intramicellar self-quenching effects have an influence on the excited-state lifetime, and the mechanism of self-quenching has been determined. Deactivation of [Ru(bipy)3] by [Co(EDTA)] has been studied in a micellar environment and found to occur by electron transfer at diffusion-controlled rates a stereoselective effect has been observed. ... 

Quenching of Ru(bipy)32+ by the organic cations trans-1,2-bis(N-methYl-4-pyridyl)ethylene and l,l -dimethy 1-4,4 -bipyridine (paraquat ) and by the transition metal ion complexes Fe(H20)g and Ru(NH3) 3+ occurs at near diffusion controlled rates (241). In all four cases flash studies indicated that electron transfer is a principal component of the quenching mechanism. Selective excitation of Ru(bipy)3 in the presence of these quenchers (Qqx produced the oxidized ruthenium complex, Ru(bipy)33+, and the reduced quencher, Qj-gd quenching... 

A more detailed picture of electron transfer processes involving Ru(bipy) 3 was provided by a study of the quenching of this excited species by a series of nitrobenzene derivatives (245). The dependence of the quenching rate constant on the reduction potential of the quencher is shown in Fig. 11. The observed dependence is in excellent agreement with that expected for quenching which involves oxidation of the excited ruthenium complex. 

Quenching of the ( CT)[Ru(bipy)3] by [Cr(bipy)]3 has been studied. This is via electron transfer to the Cr complex and a rapid back reaction. The ruthenium complex will also quench the 727 nm emission of the metal-centred doublet excited state of the chromium species, by a similar mechanism. Evidently both ligand- and metal-centred excited states can be quenched by bimolecular redox processes. A number of Ru complexes, e.g. [Ru(bipy)3] and [Ru(phen)3] also have their luminescence quenched by electron transfer to Fe or paraquat. Both the initial quenching reactions and back reactions are close to the diffusion-controlled limit. These mechanisms involve initial oxidation of Ru to Ru [equation (1)]. However, the triplet excited state is more active than the ground state towards reductants as well as... 

Ruthenium and Osmium.—The quenching of the luminescent excited state of [Ru(bipy)3]8+ has continued to receive attention.72-78 As discussed in last year s Report, controversy exists as to whether this process for Co111 complexes proceeds via electron-transfer (20) or energy-transfer (21). Navon and Sutin72 have obtained... 

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