Quenching of excited

Hooymayers HP, Alkemade CTJ (1966) Quenching of excited alkali atoms and related effects in flames Part II. Measurements and discussion. J Quant Spectrosc Radiat Transfer 6 847-874... 

On the other hand, carbonyl quenching by polyenyl radicals in PVC has been invoked in order to account for autoinhibition during photooxidative degradation (52). Some workers have mentioned the possibility of singlet oxygen formation in PVC via the quenching of excited polyenes (25,29) or cyclohexadienes (53). 

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. 

An example where electron transfer from PhO- is important comes from a related publication on the reaction of phenol with O2 where [Ru(bpy)3]2+ is used as a photosensitizer (14). In acidic media the reaction involves generation of 02 by quenching of excited [Ru(bpy)3]2+ reaction of 2 with phenol leads to the production of benzoquinone. The quantum yields for benzoquinone production are highly pH dependent, showing a sharp peak at pH 8.4. This unusual pH dependence arises from the competition of several pathways, and one of the most important being the electron-transfer quenching of [ Ru(bpy)3]2+ by PhO- ... 

Figure 7.16 Photoredox system for the oxidation of water to oxygen based on oxidative quenching of excited Ru(bpy)2+ by the sacrificial Co(NH3)5C12+ Reprinted from C. Kutal, Photochemical Conversion and Storage of Solar Energy , Journal of Chemical Education, Volume 60 (10), 1983. American Chemical Society...

A photoredox system for the production of oxygen from water using Ru(bpy)3+ as a sensitiser is shown in Figure 7.16. This system involves oxidative quenching of excited Rufbpy) by the Co(III) complex Co(NH3)5C12+ ... 

The effects of photophysical intermolecular processes on fluorescence emission are described in Chapter 4, which starts with an overview of the de-excitation processes leading to fluorescence quenching of excited molecules. The main excited-state processes are then presented electron transfer, excimer formation or exciplex formation, proton transfer and energy transfer. 

The occurrence of at least one bimolecular reaction (besides quenching) of excited 4,4 -dinitrobiphenyl with methoxide ion has been established from linear... 

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). 

For a more detailed description of quenching of excited S02 in the atmosphere after light absorption, see Calvert and Stockwell (1984). 

Rate constants for Oj-quenching of excited singlet and triplet state molecules. 

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. 

However, the recent observation of quenching of excited singlet states by conjugated dienes279 casts considerable doubt on the original conclusion. 

Quenching of Excited Molecules Through Proton Transfer. An aromatic molecule such as benzene cannot be protonated in the ground state even in strong acids... 

B. (Jih iwhiiig of fluorescence by aO. The oxygen quenching of fluorescence of aromatic hydrocarbons both in solution and in vapour phase is in general diffusion-controlled. 1 he rate constants for the 02-quenching of excited singlet and triplet states are given in Table 8.2... 

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