Quenching light emission

Aggregation normally quenches light emission what is the cause for this abnormal AIE phenomenon To address this question, we designed and carried out more experiments. When a dilute dioxane solution of 3 (lOjiM) is cooled, the intensity of its PL spectrum is progressively increased in a nonlinear fashion (Fig. 6A). When cooled from room temperature to below the melting point (11, Z°C) of the solvent, the liquid solution changes to a solid glass. The intramolecular rotations or... 

Effect of pH. The light emission from most bioluminescence systems is affected by the pH of the medium, and some luciferases and photoproteins can be made inactive at certain pH ranges without resulting in permanent inactivation. For example, the luminescence of euphausiids can be quenched at pH 6, the luminescence of aequorin can be suppressed at pH 4.2-4A, and the luciferase of the decapod shrimp Oplophorus becomes inactive at about pH 4. In the case of Cypridina luminescence, however, the acidification of an extract to below pH 5 results in an irreversible inactivation of the luciferase. 

When H2O2 is a necessary component of a luminescence system, it can be removed by catalase. If a luminescence system involves superoxide anion, the light emission can be quenched by destroying O2 with superoxide dismutase (SOD). The ATP cofactor usually present in the fresh extracts of the fireflies and the millipede Luminodesmus can be used up by their spontaneous luminescence reactions, eventually resulting in dark (nonluminous) extracts containing a luciferase or photoprotein. The process is, however, accompanied by a corresponding loss in the amount of luciferin or photoprotein. The use of ATPase and the elimination of Mg2+ in the extract may prevent such a loss. 

Certain compounds store the absorbed energy over a longer period and only emit it as light under the influence of heat or IR radiation. This process is called stimulation. The opposite phenomenon, in which the light emission is decreased by the action of heat or IR radiation on luminescent materials, is known as quenching. 

Chemiluminescence in many reactions is hard to detect because the efficiency of light emission is low. Thus, even though the excited state may be formed in high yield, it may be quenched by other species more efficiently than it loses energy by emission. This fact can be used to advantage by adding a substance... 

Luminescent ruthenium(II) polypyridine indole complexes such as [Ru (bpy)2(bpy-indole)]2+ (37) and their indole-free counterparts have been synthesised and characterised [77]. The ruthenium(II) indole complexes display typical MLCT (djt(Ru) tt (N N)) absorption bands, and intense and long-lived orange-red 3MLCT (djt(Ru) -> Ti (bpy-indolc)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. In contrast to the rhenium(I) indole complexes, the indole moiety does not quench the emission of the ruthenium(II) polypyridine complexes because the excited complexes are not sufficiently oxidising to initiate electron-transfer reactions. Emission titrations show that the luminescence intensities of the ruthenium(II) indole complexes are only increased by ca. 1.38- to... 

Designing a cluster that, upon impact, favors electronic excitation is of interest because, so far, all the experiments for detecting visible/UV light emission from impact heated clusters have, as far as we know, failed. (Possibly, the phenomenon of shuttle afterglow can be considered an exception to this statement). It could be that any electronically excited states that are formed axe very effectively quenched by the coated surfaces that are used as targets. It is however of some concern that the lowest energy indication of nonadiabaticity is electron emission. Of course, this emission could be due to the population of highly promoted (nearly united atom ")... 

Hopefully, the recognition process should induce a change of the magnitude of light emission intensity of two orders of magnitude or more. This generates a situation in which fluorescence is at first fully quenched (e.g. before substrate... 

In the previous section it has been shown that the interaction of a transition metal ion with the recognizing portion of a two-component system such as 1 may induce the quenching of the light emission of the proximate fluorophore. Determining whether fluorescence quenching is due to an eT or an ET mechanism is not a trivial problem trom an experimental point of view. 

Preliminary experiments showed that the light emission of the zinc porphyrins was strongly quenched in the case of the metallo-rotaxanes, and, remarkably, also in the case of the free [2]-rotaxane. Whereas for the metallo-rotaxanes, the possibility that the central metal-complex ftagment participates in the quenching process cannot be ruled out, for the [2]-rotaxane, it is clear that the only mechanism is through-space electron transfer to the gold(III) porphyrin moiety appended to the macrocycle. 

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