Ruthenium excited state formation

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] ... 

There are various potential applications of photophysical phenomena in analytical chemistry. The relatively short lifetimes of most excited states, however, is a serious drawback to the construction of practical devices but studies which focus on finding ways to extend triplet lifetimes have now been described by Harriman et al. Kneas et al. have examined new types of luminescent sensor on polymer supports, and both Neurauter et al. and Marazuela et al. have designed sensors based on the ruthenium(II) polypyridine complex for the detection of carbon dioxide. A system, based on the formation of twisted intramolecular charge transfer states, has been devised for measuring the molecular weight of polymeric matrices (Al-Hassan et a/.), and the chemical reactivity at the interface of self-assembled monolayers has been assessed using fluorescence spectroscopy (Fox et al). 

Ru(bipy)3] can be generated by reductive quenching of excited state [Rufbipy)]] " (see below) or by controlled potential electrolysis of [Ru(bipy)3] " at — 1.42 V. [Ru(btpy)3] have been generated electrochemically and their absorption spectra are consistent with the formation of charge localized ruthenium(II)-bipy radical species. Comparison of the electronic spectra for [Ru (bipy)3] shows the progressive growth of a band near 340 nm which is observed also for free (bipy ) radical anion, and the concomitant collapse of the (bipy ) transition near... 

Ruthenium. Reduction of [Ru(bipy)s] + by eaq (Jk = 5 x 10 M S ) results in the simultaneous formation of (a) [Ru(bipy)3] + (38% yield), the lowest charge-transfer state of [Ru(bipy)3] + (6) [Ru(bipy)3] (>55% yield), which is a different excited state or co-ordinated radical complex that is longer lived than [Ru(bipy)g] + and is not converted into it and (c) ground-state [Ru(bipy)3] (< 7 % yield). Since by its nature eaq most probably reduces by direct electron transfer, the formation of [Ru(bipy)3] + as a major product can be rationalized in terms of the Marcus theory which predicts that transfer will occur into excited states of the acceptor if the redox reaction is highly exoergic. 

The enthalpy is lower than the energy required to produce the lowest excited state, still exceeding the triplet state energy, 3R, which in turn produces IR by subsequent annihilation of 3R (triplet-triplet annihilation, TTA). ECL of ruthenium tris-bipyridyl-type derivatives falls in this category. Additionally, ion annihilation can also follow E-route, ensuing the formation of excimers (excited dimers) and exciplexes (excited complexes). 

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