Phosphorescence emission quenching

The results of this study show a definite quenching of the 418 nm phosphorescence emission of DMT. One would expect that the quenching effect, in a rigid glass, would fit the Perrin model (73). A plot in In 4>0/4> versus concentration of 4,4 -BPDC yielded a straight line, the slope of which was identified with NV. The radius, R, of the active volume of quenching sphere was calculated by the following equation ... 

The Stern-Volmer method of monitoring the quenching of luminescence can also be applied to the quenching of phosphorescence emission. 

Quenching experiments show that the phosphorescence emission is strongly quenched by oxygen, whereas the presence of oxygen has no... 

Figure 10.5 Quenching by oxygen affects the phosphorescence emission arising from Dj but has no effect on the photosolvation reaction that occurs from Q, Adapted from F. Scandola and V. Balzani, Energy-Transfer Processes of Excited States of Coordination Compounds , Journal of Chemical Education, Volume 60 (10), 1983. American Chemical Society...

The fluorescence of purified histones has been studied by several different groups, 90 95) with the most detailed studies being on calf thymus histone HI. Histone HI, which binds to the outside of core particles, contains one tyrosine and no tryptophan. This protein exhibits a substantial increase in fluorescence intensity in going from a denatured to a folded state.<90) Collisional quenching studies indicate that the tyrosine of the folded HI is in a buried environ-ment.(91) Libertini and Small(94) have identified three emissions from this residue when in the unfolded state with peaks near 300, 340, and 400 nm. The 340-nm peak was ascribed to tyrosinate (vide infra), and several possibilities were considered for the 400-nm component, including room temperature phosphorescence, emission of a charge transfer complex, or dityrosine. Dityrosine has the appropriate spectral characteristics, but would require... 

It is clear that the wide range of protein phosphorescence lifetimes is due to various specific quenching mechanisms kq) or due to flexibility of the tryptophan site, thereby affecting km. It also follows that phosphorescence will be very sensitive to conformational fluctuations since subtle changes in distance or orientation relative to a specific quenching moiety within the protein will affect the lifetimes dramatically. The phosphorescence emission from protein tryptophan remains relatively unexplored in terms of investigation of dynamic structure-function relationships. 

The only materials that have been examined for this purpose to date have been dienes and other polyenes.12 The major liability of these substances is their chemical reactivity. The finding that 1,3,5-trans-hexatriene quenches the phosphorescent emission from phenanthrene but does not have a significant effect on the fluorescent emission from 1,3,5,7-tetraphenylisobenzofuran indicates that chemical reactivity may not be too severe a problem, and that triplet quenchers may be effective tools for mechanistic work in ECL. Here too, further study is indicated. Unfortunately, or perhaps significantly, the compounds that produce the brightest emission on redox stimulation—1,3,4,7-tetra-phenylisobenzofuran and rubrene—have no detectable phosphorescence. Studies with sensitizers and quenchers have failed to produce any evidence regarding their triplet levels.12 Thus the mechanism of anni-hilative emission remains uncertain. 

Figure 4. "Stern-Volmer" quenching plot of the phosphorescence emission of B phenylpropiophenone according to eq. 4 ...

Phosphorescence most commonly follows population of Ti via ISC from Si, itself excited by absorption of light. The Ti state is usually of lower energy than Si, and the long-lived (phosphorescent) emission is almost always of longer wavelength than the short-lived (fluorescent) emission. The relative importance of fluorescence and phosphorescence depends on the rates of radiation and ISC from Si the absolute efficiency depends also on intermolecu-lar and intramolecular energy-loss processes, and phosphorescent emission competes not only with collisional quenching of Ti but also with ISC to So-... 

In photo-oxidized polymers, HAS may meet excited chromophores (Ch ) such as residues of polymerization catalysts or carbonyls arising in oxidized PO. Attempts were made to obtain information on the ability of HAS or derived NO to quench Ch [213, 214], The phosphorescence emissions from sensitizers anthraquinone, benzophenone or benzhydrol were not affected by HAS. These data indicate that quenching ability is lacking in the HAS mechanism [214],... 

The protection against quenching offered by the CD cavity allowed, in some cases, the observation of phosphorescence emission in solution. Phosphorescence from 1-chloronaphthalene was observed in the presence of 10 M P-CD by steady-state excitation, while no signal could be detected in... 

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