Quenching, fluorescent pigment

Unfortunately, the fluorescent effect is not directly proportional to the concentration of colorant present, since there is considerable quenching if quite low concentrations are exceeded. The light fastness of the fluorescent pigments is also less than that of many other organic pigments now available, but improvement can be achieved using overlayers containing ultra-violet absorbers. This is an area in which further research will clearly be needed. 

The presence of light-scattering mineral pigments such as titanium dioxide or iron oxides will quench the flourescent effect. Similarly, excessive concentration of the fluorescent acts to prevent reemission of light and is a waste of money. 

The fluorescence emission of chlorophylls and bacteriochlorophylls is invariably emitted from the lowest energy excited sate, with typical Stokes shifts of 10-15 run from the Qy absorbance maximum. Fluorescence lifetimes of 2-5 ns are usually observed for monomeric pigments in organic solvents. Fluorescence of chlorophyll and bacteriochlorophyll in vivo is very strongly quenched excited-state lifetimes are typically a few tens of picoseconds and fluorescence quantum yields are at most a few percent. The... 

Theoretical calculations have been made for photosynthetic pigments . An extensive review of models of energy and electron transfer events of synthetic molecules for photosynthesis has been prepared by Wasielewski . Other studies have made on tetraphenylporphyrin-polypeptide pigments , photosensitization of triplet carotenoids , fluorescence yields and lifetimes for bacteriochlorophyll c , triplet yields and ESR of chlorophyll 3 8 and quenching processes of pheophytin 539 ... 

A microscopic fluorescence spectrum is potentially very informative, since it reflects stoichiometric ratios, efficiencies of electronic excitation transfers among the pigment-protein complexes, and quenching mechanisms inherent in the photo synthetic reactions. Since the multiple fluorescence bands are overlapping, spectral detection based on a polychromator and multichannel detector is more informative than detection using a few channels based on dichroic mirrors and band-pass filters. 

Maximizing sensitivity with fluorescence detectors - the concentration of other sample components, e.g. pigments, must not be so high that they cause quenching of fluorescence. 

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