Metal luminescence intensity

In this section, we discuss the intensity of the metal luminescence obtained upon ligand excitation on the basis of the product of the metal luminescence quantum yield upon excitation at a certain wavelength and the molar absorption coefficient of the ligand in the complex at the same wavelength (Table 7). We would like to recall that the metal luminescence intensity is the photophysical property of main interest in this research dealing with the antenna effect in Eu3+ and Tb3+ complexes. Furthermore, this quantity is determining for some applications of these compounds (Section III). 

Nevertheless, the demand for complexes characterized by higher metal luminescence intensities remained. Actually, other complexes that were subsequently studied (Section IV) exhibited satisfactory metal luminescence intensities but, up to now, drawbacks related to instability of the complexes in water or their decomposition upon attachment to the biomolecule rendered their application impossible. 

Luciferase-catalyzed luminescence of luciferin. Odontosyllis luciferin emits light in the presence of Mg2+, molecular oxygen and luciferase. The relationship between the luminescence intensity and the pH of the medium shows a broad optimum (Fig. 7.2.8). The luminescence reaction requires a divalent alkaline earth ion, of which Mg2+ is most effective (optimum concentration 30 mM). Monovalent cations such as Na+, K+, and NH have little effect, and many heavy metal ions, such as Hg2+, Cu2+, Co2+ and Zn2+, are generally inhibitory. The activity of crude preparations of luciferase progressively decreases by repeated dialysis and also by concentrating the solutions under reduced pressure. However, the decreased luciferase activity can be completely restored to the original activity by the addition of 1 mM HCN (added as KCN). The relationship between the concentration of HCN and the luciferase activity is shown in Fig. 7.2.9. Low concentrations of h and K3Fe(CN)6 also enhance luminescence, but their effects are only transient. 

BCPDA is a tetradentate ligand, and forms 1 1 complexes in these conditions. The metal ion is thus coordinatively unsaturated, and also binds a number of water molecules, which can lead to non-radiative quenching of the metal-centered excited state (vide supra). These must be removed by drying to achieve optimal luminescence intensity. This form of assay is, in fact, slightly less sensitive than DELFIA. 

Fig. 11 Plot of the luminescence intensity of an aqueous solution of Au23 against the ions added externally to the solution. The concentration of Au23 was the same for all the experiments. Clusters showed specific reactivity toward Cu2+ ions with significant quenching of luminescence. Photographs of the aqueous solution of Au23 in the presence of externally added ions under UV light irradiation are also given. The photograph was collected immediately after the addition of metal ions [15]...

Addition of benzene to a solution of / -CD8 causes a two-fold enhancement of Eu3+ luminescence intensity. The stability constant of the complex between / -CD8 and benzene ( 200) is comparable to that of the complex with the native /i-CD. In contrast, benzoic and naphthoic acids show much stronger associations with / -CD8 than with native / -CD because association is assisted by the interaction between the carboxylic groups and the metal ion. Moreover, the enhancement factor of the luminescence is larger. 

The increase in luminescence intensity and the strong blue shift are suggestive of an interlayer region that is devoid of free water or the water molecules are either frozen or immobile and cannot effectively solvate the initially produced MLCT excited state of the metal complex. The red shift of the absorption spectrum and the... 

Yb(5d)(H20)3]Cl, and [Yb(5d)(CoP] (fig. 12) where CoP is the cyclopentadienyl-tris(dieth-ylphosphito)cobaltate(I) anion (see fig. 13) for which the luminescence intensity increases in the proportions 1 22 36 62 271, upon excitation at 512 nm (Meng et al., 2000). The effect of coordinated water molecules on the metal-centered fluorescence intensity is clearly seen in the more than four-fold enhancement obtained by replacing the three water molecules in [Yb(5d)(H20)3 ]C1 by CoP the 2F5/2 lifetime of the latter complex (40 ps) is also much longer than lifetimes reported for other Ybm porphyrinates. In addition, the cobaltate anion rigidities the molecule, which results in a much finer structure of the ligand-field split electronic levels. 

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