Luminescent quenchers

The ion Fe has the electronic configuration 3d. It is characterized by extremely strong absorption and is the strongest visible luminescence quencher in minerals, but it has an emission band in the IR part of the spectrum. 

In most cases, quenching of luminescence of CdS colloids is determined by the reactions of interfacial electron transfer involving either electron or hole. So, study of this process is a convenient method for establishing the regularities of key steps of redox photocatalytic reactions over CdS. In addition, using of various luminescence quenchers (anions, cations, and neutral molecules) allows to reveal the nature of electron capture sites at the CdS surface. 

Therefore, the suggested equation (2.19) reflects adequately a variation in the properties of luminescence quenchers and describes well the experimental data as a whole. In addition, the data suggest that for the colloids obtained with an excess of the sulfide ions, the quencher adsorption site is represented most likely by the negatively charged surface sulfur atoms, on which the cations adsorb readily while the anions adsorb poorly. Actually, in this case, the dominant surface defects are either the vacancies of the cadmium ions, or... 

The ability of a luminescence quencher molecule to adsorb on the surface of ultradispersed colloidal semiconductor in aqueous solutions was shown to depend mainly on the charge of the colloidal particle surface and the charge of quencher ions. 

Rh(phi)2(phen)]3+ is a particularly suitable luminescence quencher for our investigations of electron-transfer reactions on DNA. Its electronic properties are favorable for electron transfer, and this rhodium complex is primarily sequence neutral, so that nearly random binding of the donor and acceptor is expected. Moreover, the photocleavage reaction actually allows us to identify the positions of binding of the acceptor to the DNA double helix. 

Finally, there have been reports that deal with other forms of spectral detection. A platinum (Il)-coproporphyrin reagent has been evaluated for phosphorescent labelling of oligonucleotides. The presence of the label had little effect on conjugation, and labelled primers were effective in PCR reactions. A silicon nanoparticle conjugated to ODNs acted as a luminescent label, and a molecular beacon (see later) has been prepared which contains a photoluminescent dye (Ru(II)(bpy)3) and the luminescent quencher Black Hole Quencher-2 . ... 

FIGURE 3.1. Overall mechanism for Alq3 degradation in the presence of water. Water replaces one of the oxyquinolate ligands on the complex. The free Hq can then go on to form oxidized species which act as luminescence quenchers. 

The preceding analysis and review of the literature indicate a need for additional types of experiments to study triplet mobility in polymers. One experiment which has been particularly useful in studies of singlet energy migration in polymers, involves determination of the quenching of donor emission by a known mole fraction of a copolymerized luminescent quencher (26). We have extended this approach to the study of triplet states. The polymers chosen for study are homopolymers of isomeric acetonaphthyl methacrylates (aceto-NMA, 1). A related monomer, 2,4-diaceto-l-naphthyl... 

A variation of the quenching method leading to Eq. (25) is to follow the decay of the triplet state from the emission of a luminescent quencher, which is much more intense than the phosphorescence of the probe [192]. In this case, the observed rate constant corresponds to the growth and subsequent decay in the emission profile of the quencher. However, an additional rate constant, corresponding to the emission lifetime of the quencher, has to be included in Eq. (25). The exit rate constant was determined to be 2.5 x 10 s for 1-bromonaphthalene when quenched by either Eu or Tb. This value is the same (Table 16) as that determined using the anionic quencher, NOf [62], showing that this method is useful. However, care should be taken to eliminate the possibility of reverse energy transfer. 

Nevertheless, a buildup of high concentrations of charged reaction products (dianions or bipolarons, or their further decay products) is clearly detrimental for two reasons they are luminescence quenchers,(27) and they are immobile, so that they constitute a fixed space charge which raises the voltage required for electron injection. In previous publicationsfJ, 16) we have suggested... 

Both static and dynamic quenching require contact of the luminophore with a quencher molecule. This requirement is the basis of the many applications of luminescence quenching. Because there are so many molecules that can act as luminescence quenchers, an appropriate quencher can be selected for any luminophore under study in order to investigate specific properties of the luminophore. An example of biochemical applications of luminescence quenching is given later in this section. 

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