Efficiency of fluorescence

Quantitative aspects. The total fluorescence intensity, F, is given by the equation F = Ia(f> where Ia is the intensity of light absorption and 4>f the quantum efficiency of fluorescence. Since 70 = 7a + 7t where 70 = intensity of incident light and 7t = intensity of transmitted light, then... 

In order to clear up the mechanism of inactivation of excited states, we examined the processes of quenching of fluorescence and phosphorescence in PCSs by the additives of the donor and acceptor type253,2S5,2S6 Within the concentration range of 1 x 1CT4 — 1 x 10"3 mol/1, a linear relationship between the efficiency of fluorescence quenching [(/0//) — 1] and the quencher concentration was found. For the determination of quenching constants, the Stem-Volmer equation was used, viz. 

The data in Figure 14 imply that the efficiency of fluorescence quenching by acceptors grows simultaneously with an increase in electron affinity of the quenchers. 

The quantum efficiency of fluorescence of a molecule is decided by the relative rates of fluorescence, internal conversion and intersystem crossing to the triplet state. Up to the present time it has proved impossible to predict these relative rates. Thus, whilst it is now possible to calculate theoretically the wavelengths of maximum absorption and of maximum fluorescence of an organic molecule, it remains impossible to predict which molecular structures will be strong fluorescers. Design of new FBAs still relies on semi-empirical knowledge plus the instinct of the research chemist. 

Griseofulvin exhibits both fluorescence and luminescence. A report by Neely et al., (7) gives corrected fluorescence excitation (max. 295 nm) and emission (max. 420 nm) spectra, values for quantum efficiency of fluorescence (0.108) calculated fluorescence lifetime (0.663 nsec) and phosphorescence decay time (0.11 sec.). The fluorescence excitation and emission spectra are given in Figure 7. 

Among the rarest of the rare earths as an oxide used to enhance the red in color computer monitors and televisions also improves efficiency of fluorescent lights. 

The third rule of practical value concerns the intensity of fluorescence obtained and its variation with frequency of exciting light. The rate of emission of fluorescence is by definition equal to the rate of light absorption, measured in quanta, multiplied by the quantum efficiency of fluorescence, i.e.,... 

In dianions of xanthene dyes although halosubstituents decrease the quantum efficiency of fluorescence, phosphorescence efficiency is not increased proportionately. The phosphorescence lifetime decreases with fa. It is suggested that in these dyes, besides enhancement of Sx intersystem crossing rates, S nonradiative transition is promoted by heavy atom... 

For aromatic hydrocarbons, the quantum efficiencies of fluorescence and phosphorescence in low temperature glasses (Appendix H) such as EPA (ether isopentane ethyl alcohol in the ratio 2 2 5) add up to unity. This suggests that direct nonradiative decay from Si —> S0 is of very low probability. All the nonradiative paths to the ground state are coupled via the triplet state. The sequence of transfers is ... 

The exponential dependence of the efficiency of fluorescence quenching on the distance between a donor and an acceptor may be explained by the tunneling mechanism of electron transfer from a singlet-excited molecule of the donor to the acceptor. Indeed, in case of stationary excitation of donor particles, the value of J is determined by the stationary concentration n of the excited donor particles J = An where A is a constant. The value of n is, in its turn, inversely proportional to the rate constant, k, of deactivation of excited particles nft = nJexcexciting light, quantum yield of excited molecules, and n is the concentration of non-excited donor molecules. Thus, J = AnJexc4>lk. Hence, one can easily obtain... 

Since the efficiency of fluorescence quenching of the sensitizer paralleled the oxidizability of the arene in a series of substituted alkyl benzenes, the reaction was thought to proceed through electron transfer followed by protonation and trapping of the radical by oxygen. 

Melhuish, W. H. (1961) Quantum efficiencies of fluorescence of organic substances effect of solvent and concentration of the fluorescent solute, J. Phys. Chem. 65, 229-235. 

Most biochemical assays used to determine the potency of inhibitors against (1) aminopeptidases and (2) endopeptidases with minor contributions to the substrate binding efficiency by the S site are based on the measurement of fluorescence intensity (FI). The FI readout principle is shown in Figure 2.2. The dynamic range of the FI readout basically scales with the fluorescence quantum yield, that is, the efficiency of fluorescence emission of the dye label. For the FI readout, peptide substrates with fluorogenic groups such as acetylmethoxycoumarin (AMC), 7-amino-4-trifluoromethyl... 

Quantum Yield Efficiency of fluorescence percentage of incident energy emitted after absorption. The higher the quantum yield, the greater the intensity of the fluorescence, luminescence, or phosphorescence. See Papp, S. and Vanderkooi, J.M., Tryptophan phosphorescence at room temperature as a tool to study protein structure and dynamics, Photochem. Photobiol. 49, 775-784, 1989 Plasek, J. and Sigler, K Slow fluorescent indicators of membrane potential a survey of different approaches to probe response analysis, J. Photochem. Photobiol. 33, 101-124, 1996 Vladimirov, Y.A., Free radicals in primary photobiological processes, Membr. Cell Biol. 12, 645-663, 1998 Maeda, M., New label enzymes for bioluminescent enzyme immunoassay, J. Pharm. Biomed. Anal. 30, 1725-1734, 2003 Imahori, H., Porphyrin-fullerene linked systems as artificial photosynthetic mimics, Org. Biomol. Chem. 2, 1425-1433, 2004 Katerinopoulos, H.E., The coumarin moiety as chromophore of fluorescent ion indicators in biological systems, Curr. Pharm. Des. 10, 3835-3852, 2004. 

Marras SA, Kramer FR, Tyagi S. Efficiencies of fluorescence resonance energy transfer and contact-mediated quenching in oligonucleotide probes. Nucleic Acids Res. 2002 30 el22. 

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