Quenching of excited states

In this group, there are collisional interactions, which are responsible for quenching of excited states by molecular oxygen, paramagnetic species, heavy atoms, etc. [1, 2, 13-15]. Probability of such quenching can be calculated as ... 

T.J. Meyer The observation of emission from the films is not surprising. The films described are rather thick and consist of the equivalent of many molecular monolayers. No doubt we are observing emission from layers well away from the electrode surface. Emission is not observed from thin films, suggesting that efficient quenching of excited states in the layers near the electrode does occur. 

M. Z. Hoffman, F. Bolleta, L. Moggi and G. L. Hug, Rate Constants for the Quenching of Excited States of Metal Complexes in Fluid Solution, J. Phys. Chem. Ref. Data, 18, 219 (1989). 

The relatively long lifetimes of the excited states of these complexes have made them particularly attractive in the study of electron and energy-transfer quenching of excited states through organic bridges. In addition, the more positive redox potentials of these ions, compared with their pentaammine counterparts, mean that the mixed-valence ions are not air sensitive, thus facilitating spectroscopic measurements. 

Fig. 9. Plots of log(k[M-1 s 1] for fluorescence quenching of excited states [21, 40]. The solid curve is a Rehm-WeBer plot and the broken one a Marcus plot, both with X = 9.6 kcal mol-1 = 40 kJ mol-1. The dotted curve corresponds to a Marcus plot with X = 38 kcal mol-1 = 159 kJ mol-1 (X = reorganization energy, AG° = corrected standard free energy change of electron transfer) — taken from Ref. [lb]...

With site-directed mutation and femtosecond-resolved fluorescence methods, we have used tryptophan as an excellent local molecular reporter for studies of a series of ultrafast protein dynamics, which include intraprotein electron transfer [64-68] and energy transfer [61, 69], as well as protein hydration dynamics [70-74]. As an optical probe, all these ultrafast measurements require no potential quenching of excited-state tryptophan by neighboring protein residues or peptide bonds on the picosecond time scale. However, it is known that tryptophan fluorescence is readily quenched by various amino acid residues [75] and peptide bonds [76-78]. Intraprotein electron transfer from excited indole moiety to nearby electrophilic residue(s) was proposed to be the quenching... 

Hoffman MZ, Bolleta F, Moggi L, Hug GL. Rate constants for the quenching of excited states of metal complexes in fluid solution. / Phys Chem Ref Data 1989 18 219-543. 

Apart from iodide ion, radicals are efficient quenchers of excited states of molecules [16] the processes of quenching of excited states of various molecules by radicals were studied earlier in detail [17 - 19]. It was shown that the triplet states of usual cyanine dyes are mainly quenched by the mechanism of acceleration of the intersystem crossing to the ground state (T-So). In this case, the quenching process is described by the following scheme ... 

N. Sabattini, M.Guardigliandl. Manet, 1996,23,69 (antenna effect in encapsulated complexes). G.E. Buono-core and H.LiB. Marciniak, Coord. Chem. Rev., 1990, 99,55 (quenching of excited states by lanthanide ions and chelates in solution). 

Generation of excited triplet states is normally achieved as a result of (iv) above and, once formed, they may decay by processes analogous to (i)—(iv) with the obvious distinction that radiative decay of triplet states is termed phosphorescence, and that radiationless transition of excited triplet states, back to ground singlet states, involves intersystem crossing. Whilst there are very many mechanisms whereby so called quenching of excited states may occur (1,2), and a full discussion is outside the scope of this article, a large part of the review will be... 

Quenching of excited-state [Ru(bipy)3] by reduced blue proteins involves electron transfer from the Cu with rate constants close to the diffusion limit for electron-transfer reactions in aqueous solution. It is suggested that the excited Ru complex binds close to the copper-histidine centre, and that outer-sphere electron transfer occurs from Cu through the imidazole groups to Ru. Estimated electron-transfer distances are about 3.3 A for plastocyanin and 3.8 A for azurin, suggesting that the hydrophobic bipy ligands of Ru " penetrate the residues that isolate the Cu-His unit from the solvent. ... 

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