Paraquat quencher

Several systematic studies of the driving force dependence of the rate of forward and back ET in type 1 dyads (see Fig. 1) were carried out during the past decade. As might be expected, the type 1 dyads used in these investigations consist of covalently linked assemblies of metal complexes and organic quenchers used in early studies of bimolecular photoinduced ET reactions. Thus, the type 1 dyads consist of polypyridine Ru(II) complexes linked to pyridinium acceptors such as paraquat and diquat (quatemized 2,2 -bipyridine). 

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... 

Fluorescence quenching experiments (with diquat dichloride), deuterium kinetic isotope effects, and the effects of triplet state quenchers have suggested a mechanism involving primary electron transfer to singlet excited paraquat [(184) and (185)]. 

Flash photolysis experiments show that [Ru(bipy)3] + ion once excited dispro-portionates into [Ru(bipy)3] + and [Ru(bipy)3]+ ions. The reaction is catalysed by oxidative quenchers like the paraquat dication, and also by reductive quenchers such as iV-dimethylaniline. ... 

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