Quenching fluorescence lifetimes

Several hundreds of covalent quinone-quinone and porphyrin-quinone compounds have been synthesized and tested for light-induced charge transfer by fluorescence quenching, fluorescence lifetime, and flash photolysis experiments. 

In a comparison of fluorescence spectra between the ester and thioester derivative crystals of PDA, the ester crystal shows a strong emission whereas the thioester crystal fluoresces much more weakly. For example, the intensity of a PDA methyl thioester crystal is about one-thousandth of that of a PDA methyl ester crystal. Furthermore, the fluorescence lifetime of mixed crystals which consist of a large amount of PDA methyl ester and a small amount of the corresponding thioester moiety is much shortened, compared to the lifetime of pure PDA methyl ester crystals. In quenching experiments in solutions of PDA ester, the fluorescence of the PDA ester is dramatically quenched by thioacetate. Similar behaviour has been obtained with several types of diolefin derivatives having a thioester moiety, where crystal structures are isomorphous with the corresponding ester derivatives. 

Quantitative analysis of the results obtained has shown that a single eosin guest is sufficient to completely quench the fluorescence of any excited dansyl unit of the hosting dendrimer. Fluorescence lifetime measurements indicated that the dye molecules can occupy two different sites (or two families of substantially different sites) in the interior of the dendritic structure. 

To perform structural research on a food stuff into which a colorant is incorporated, special properties of fluorescing molecules are exploited fluorescence efficiency, fluorescence lifetime, fluorescence quenching, radiationless energy (Foerster) transfer, stationary or time-dependent fluorescence polarization and depolarization." Generally, if food colorants fluoresce, they allow very sensitive investigations which in most cases cannot be surpassed by other methods. 

Jean JM, Hall KB (2001) 2-aminopurine fluorescence quenching and lifetimes role of base stacking. Proc Natl Acad Sci USA 98 37-41... 

When anisotropy increases due to fluorescence lifetime decrease being coupled to any effect of dynamic quenching. 

Holub, O., Seufferheld, M. J., Gohlke, C., Govindjee, G. J., Heiss, G. J. and Clegg, R. M. (2007). Fluorescence lifetime imaging microscopy of Chlamydomonas reinhardtii Non-photochemical quenching mutants and the effect of photosynthetic inhibitors on the slow chlorophyll fluorescence transients. J. Microsc. 226, 90-120. 

In Fig. 9.4, the results are shown of an experiment using a double (annexinA4-EYFP+ annexinA4-mCherry) transfected cell immediately after addition of the calcium ionophore ionomycin (top) and 5 min after application of ionomycin (bottom). Clearly visible is the diffuse localization of annexin A4 before relocation and the more structured localization (into membrane ruffles and filopodia) after relocation. More importantly, the EYFP fluorescence lifetime is quenched from 2.9 ns before translocation to... 

Thus, E is defined as the product of the energy transfer rate constant, ku and the fluorescence lifetime, xDA, of the donor experiencing quenching by the acceptor. The other quantities in Eq. (12.1) are the DA separation, rDA the DA overlap integral, / the refractive index of the transfer medium, n the orientation factor, k2 the normalized (to unit area) donor emission spectrum, (2) the acceptor extinction coefficient, eA(k) and the unperturbed donor quantum yield, QD. 

The dependence of the fluorescence quantum yields and lifetimes of these stabilizers on the nature of the solvent suggests that the excited-state, non-radiative processes are affected by solvation. In polar, hydroxylic solvents, values of the fluorescence quantum yield for the non proton-transferred form are significantly lower, and the fluorescence lifetimes are shorter, than those calculated for aprotic solvents. This supports the proposal of the formation, in alcoholic solvents, of an excited-state encounter complex which facilitates ESIPT. The observed concentration dependence of the fluorescence lifetime and intensity of the blue emission from TIN in polymer films provides evidence for a non-radiative, self-quenching process, possibly due to aggregation of the stabilizer molecules. 

FRET manifests itself through the quenching of donor fluorescence and a reduction of the fluorescence lifetime, accompanied by an increase in acceptor fluorescence emission. The efficiency of the energy-transfer process varies in proportion to the inverse sixth power of the distance separating the donor and acceptor molecules. Consequently, FRET measurements can be utilised as an effective molecular ruler for determining distances between molecules labelled with an appropriate donor and acceptor fluorophore, provided they are within lOnm of each other. 

The labeling can also be done by fluorescence lifetime differences, e.g., introduced by quenching pathways connected with different surroundings. This can be used for lifetime imaging methods (Chapter 1, this volume) or for distinguishing complexes of one and the same fluorescence label with, e.g., different DNA-bases. In this case, the fluorescence label is not only a label but incorporates a function which senses the environment and can therefore be regarded as a sensing fluorescence probe. 

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