Energy transfer quenching

Extrusion or elimination of small stable species such as CO2 Intramolecular energy transfer Quenching involving translational or vibrational excitation of another molecule... 

In the scheme, the assumption is made that the only important quenching event is electron transfer and that energy transfer quenching is negligible. The series of electron transfer events in the scheme are initiated by optical excitation to give the excited state and the electron transfer reactions which occur fol-... 

Energy transfer quenching. If an impurity is present whose first excited singlet state is below that of the excited state of the analyte then energy can be transferred to the impurity and fluorescence is not seen. This does not have to involve collision and non-radiation transfer can occur. Aromatic molecules are particularly a source of this interference. Removal is an option but sometimes dilution is a solution if the desired fluorescence can still be measured at lower concentration. 

Nonradiative processes (knr) can occur with a wide range of rate constants. Molecules with high knr values display low quantum yields due to rapid depopulation of the excited state by this route. The measured lifetime in the absence of collisional or energy transfer quenching is usually referred to as To, and is given by to = (kr + knr). ... 

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. 

By preparing polycyclic aromatic hydrocarbon nanocrystals grown in porous silicate films, Botzung-Appert et al. [57] have prepared potential fluorescent sensors based on electronic energy transfer quenching to an acceptor... 

Deactivation of an excited species can proceed through radiation or radiationless decays, energy transfer quenching, or electron transfer routes. The operation of artificial photosynthetic devices relies mainly on electron-transfer (ET) processes induced by an excited species [16, 17]. Two general mechanisms can be involved in the ET process of an excited species Reductive ET quenching of an excited species, S, by an electron donor D, results in the redox products S- and D+ (Fig. 4 a). Alternatively, oxidative quenching of the excited species by an electron acceptor, A, can occur (Fig. 4b), resulting in the electron transfer products S+ and A-. 

In initial two-color experiments performed with 90, and other compounds such as benzophenone (70), in benzene solvent, extensive T-T depletion was observed. This led to the assumption that upper state chemistry such as type I cleavage was efficient. However, as was pointed out above, benzene and other aromatic solvents can quench upper triplet states by energy transfer and thereby cause depletion. A reexamination of several reluctant type I systems using other solvents (particularly acetonitrile) revealed that energy transfer quenching by aromatic solvent is usually a more important upper triplet decay pathway than cleavage. 

Fluorescence resonance energy transfer (quenched fluorescence, InVitroGen Z -LYTE)... 

TABLE 12.2. Structural dimension analysis of excitation energy transfer quenching of SRIOI by ABl at the water/oil interfaces. 

The structural dimension determined by excitation energy transfer quenching of SRlOl fluorescence by ABl (see main text). 

The structural dimension at a water/DCE interface is d — 2.48, while short-range structural information about the interface obtained by the fluorescence dynamic anisotropy experiments suggests that the interface is three-dimensional-like. Taking the results obtained by molecular dynamics simulations into account, these results can be understood only by the fact that the water/DCE interface is thin ( 1 nm), but is rough with respect to the spatial resolution of the excitation energy transfer quenching method ( 7 nm), as shown in Figure 12.7. 

C. Intermolecular Electronic Energy Transfer Quenching of one excited-state species may result in transfer of electronic energy to the quenching species. Intermolecular energy transfer has become an important technique in photochemistry because it often permits the selective population or depopulation of one specific excited-state species. 

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