Concentration quenching effect

The PL quantum yield r)pl. While r]pl of many dyes is close to 100% in solution, in almost all cases that yields drops precipitously as the concentration of the dye increases. This well-known concentration quenching effect is due to the creation of nonradiative decay paths in concentrated solutions and in solid-state. These include nonradiative torsional quenching of the SE,148 fission of SEs to TEs in the case of rubrene (see Sec. 1.2 above), or dissociation of SEs to charge transfer excitons (CTEs), i.e., intermolecular polaron pairs, in most of the luminescent polymers and many small molecular films,20 24 29 32 or other nonradiative quenching of SEs by polarons or trapped charges.25,29 31 32 In view of these numerous nonradiative decay paths, the synthesis of films in which r]PL exceeds 20%, such as in some PPVs,149 exceeds 30%, as in some films of m-LPPP,85 and may be as high as 60%, as in diphenyl substituted polyacetylenes,95 96 is impressive. 

Sato-Sorensen [242,243] considered the effect of pressure on the lifetime of ruby with a high Cr + concentration ( 1 wt%) and also observed a hnear variation with pressure, r (ms) = 2.6 + 0.022P (kbar), up to 427 kbar. The low ambient pressure lifetime was attributed to concentration quenching in the sample. Although not directly discussed by Sato-Sorensen, the smaller increase in lifetime with pressure relative to that reported by Urosevic et al. [246] is also presumably due to concentration quenching effects. A reduction of the Cr + interionic separation in concentrated ruby would increase the rate of energy transfer between Cr ions and enhance concentration quenching. 

The emission bands from 1 to 5 are, respectively, Dq Fq, Dq Fj, Dq —> F2, Dq —> F3, and Dq —> F4. It was observed that the fluorescence intensity decreases with an increase of the total amount adsorbed complex. Such fact was previously observed for another europium complex-doped hybrid surfaces and could be explained based on both, the organic moiety/complex ratio, as well as concentration quenching effect. 

This behaviour is the total opposite of the concentration-quenching effect. Enhanced solid-state emission of a biphenylethene derivative 2... 

The low quantum yields in planar conjugated PHT can be explained by classical concentration quenching effects which arise from non-emissive excimer complexes intermolecular decay channels) [100],... 

A high concentration of the fluorescent dye itself in a solvent or matrix causes concentration quenching. Rhodamine dyes exhibit appreciable concentration quenching above 1.0%. Yellow dyes, on the other hand, can be carried to 5 or even 10% in a suitable matrix before an excessive dulling effect, characteristic of this type of quenching, occurs. Dimerization of some dyes, particularly those with ionic charges on the molecules, can produce nonfluorescent species. 

Spectrofluorometry presents sensitivity and selectivity greater than the absorbance spectroscopy, being more suitable for chlorophyll estimates in the nmol range and for residual amounts of derivatives in food products. Absorbance spectroscopy is satisfactory for concentrations > 1 xMP Spectrofluorometry is also more accurate for a wide range of chlorophyll a-to-chlorophyll b ratios, but it is less accurate when applied to complex sample matrices because of unpredictable quenching effects. 

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 ... 

Some initiators, for example, AIBN (azobisisobutyronitrile) and dibenzoyl peroxide exhibit a strong quenching effect. That is why, the dependence of the CL intensity on the initiator concentration (/=r Vi) is nonlinear in these cases. 

The addition of halide ions to 0.1M sulfuric acid solutions of triprolidine hydrochloride has a quenching effect on the fluorescent intensity. The degree of quenching is I > Br >C1 > F. A concentration of 10 M Cl has little effect on the fluorescent intensity, while 0.1M Cl reduces the intensity by approximately 75% of the chloride-free sulfuric acid solution. 

Concentration quenching. In this case, quenching occurs because of the formation of an association between excited state and ground state, which if homo-molecular is called the excimer formation. The subsequent processes can be radiationless or the complex can emit at much longer wavelength and effectively not be detected. 

DASPE-TFPB), respectively. The obtained solid precipitates were brightly emissive whereas that of the native DASPE-I were almost nonemissive (Fig. 7a the photo is taken under normal illumination and UV-light irradiation). This indicates that, in the solid of the ion-pair species between DASPE+ and TPB (or TFPB ), concentration quenching is effectively suppressed, and more importantly, these ion-pair complexes can generate fluorescent... 

The dependence of and S2 fluorescence intensities on the sample concentration was investigated between 10 - 10 M, and a sample concentration of less than 10 M was chosen to minimize the effect of concentration quenching. Two-photon absorption measurements were carried out by the excitation by relatively low power density (<10 photons cm" pulse ) in order to avoid the saturation effect on the laser power. Under these experimental conditions, the following rate equations for the concentration of S2 molecule is derived ... 

The carrier used for this purpose consisted of a 0.1 M phosphate buffer of pH 7. The appearance of the sensing microzone is shown in Fig. 5.5.B. The oxygen optrode used was based on a 10-pm silicone rubber film containing dissolved decacyclene as indicator (S) that was fixed on a 110-pm thick polyester support (PS). A 9-pm black PTFE membrane (I) was used for optical insulation. The dye fluorescence was found to be markedly dependent on the concentration of oxygen, which exerted a quenching effect on it. The enzyme (glutamate oxidase) was immobilized on a 150-pm thick immunoaffmity membrane (E). The sensor was prepared similarly as reported by Trettnak et al. [7]. 

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