Relative quantum yield

Heat stability The Oplophorus luminescence system is more thermostable than several other known bioluminescence systems the most stable system presently known is that of Periphylla (Section 4.5). The luminescence of the Oplophorus system is optimum at about 40°C in reference to light intensity (Fig. 3.3.3 Shimomura et al., 1978). The quantum yield of coelenterazine is nearly constant from 0°C to 20°C, decreasing slightly while the temperature is increased up to 50°C (Fig. 3.3.3) at temperatures above 50°C, the inactivation of luciferase becomes too rapid to obtain reliable data of quantum yield. In contrast, in the bioluminescence systems of Cypridina, Latia, Chaetopterus, luminous bacteria and aequorin, the relative quantum yields decrease steeply when the temperature is raised, and become almost zero at a temperature near 40-50°C (Shimomura et al., 1978). 

Calibration. Many approaches have been used to calibrate flow cytometric measurements. Including the comparison of flow and nonflow techniques (radiolabels, spectrofluorometry). In recent years, commercial standards have been introduced which are calibrated in fluorescein equivalents/particle (e.g., 3,000 or 500,000). With labeled ligands, calibration requires determining the relative quantum yield of the ligand compared to pure fluorescein and using the standards to analyze the amount bound on cells. Our ligands (fluorescein isothiocyanate derivatives) are typically 50% as fluorescent as fluorescein. 

Quantum Yields of Fluorescence. Table III lists the relative quantum yields of fluorescence of 24 3-substituted 2(lH)-pyridones. Pyridone I has the highest yield measured, which is set at 1.00. An attempt was made to measure the absolute quantum yield of I relative to rhodamine B using ferrloxalate actinometry. A Vpj value of 0.98 0.02 was obtained. However, the determination of absolute ... 

In practice it is much simpler to determine the relative quantum yield of fluorescence than the absolute quantum yield (see Table 2.1). This is done by comparing the fluorescence intensity of a given sample to that of a compound whose fluorescence quantum yield is known. For this one must... 

If the refractive indices of the solvents used for the sample and the fluorescence standard are not the same, a further correction must be made. For example, quinine sulfate in 0.1 N H2S04 (Or = 0.5) is commonly used as a fluorescence standard. If the fluorescence of the sample whose relative quantum yield is desired is determined in benzene, a correction factor of 27% must be applied in determining the relative areas under the fluorescence bands. If ethanol is used, this correction is only 5.5%. 

Table 8.5. Relative Quantum Yields and Rate Constants for Compounds (36)...

Luminescence spectroscopy is one of the most sensitive techniques for identification of impurities in dyes. The most commonly observed impurities in to-bipyridyl complexes of the type [RuL2X2] are the homoleptic tris-bipyridyl species [RuL3]2+. Since the emission quantum yields of the [RuL3]2+ complexes are significantly higher than those of the [RuL2X2] complexes, one can identify the homoleptic impurities at a level of less than 1%. This does depend, however, on the relative quantum yields, and position of the emission spectral maxima, for the complexes and impurities involved. 

The quantum yield (Q) represents the ratio between the number of photons absorbed and photons emitted as fluorescence. It is a measure of brightness of the fluorophore and represents the efficiency of the emission process. The determination of absolute quantum yield for a fluorophore is experimentally difficult. Therefore, usually relative quantum yield values are determined. To measure the relative quantum yield of a fluorophore, the sample is compared to a standard fluorophore with an established quantum yield that does not show variations in the excitation wavelength [5, 6]. 

Because only the relative quantum yields are to be determined, a single observation wavelength is sufficient and the latter is selected so that there is no emission from the acceptor1 . Then, Eq. (9.7) can be rewritten in terms of absorbances at the excitation wavelength 7d and fluorescence intensities of the donor in the absence and presence of acceptor ... 

The energy transfer efficiency for this system can be calculated from relative quantum yield of the donor... 

It has been shown that polypyridyl Rh(III) complexes induce photo-cleavages of the sugar phosphate backbone of double-stranded DNA with a higher relative quantum yield than Ru(II) complexes of phen or DIP. Thus replacement of Ru(II) ions by Rh(III) in Tris(phen) complexes, increases the efficiency of DNA photo-cleavages. However, in contrast to the Ru(II) complexes, Rh(III) samples have to be illuminated in the UV because of the absence of absorption bands in the visible region. 

Table 4 Relative Quantum Yield in the PFR of Several Substituted Phenyl Benzoates...

Eigure 5.41 summarizes the temperature behavior of decay time and quantum efficiency of red benitoite luminescence at 660 nm in the forms ln(r) and ln(q) as a functions of 1/T. In such case the luminescence may be explained using simple scheme of two levels, namely excited and ground ones. The relative quantum yield (q) and decay time (r) of the red emission may be described by simple Arhenius equations ... 

The results in Table V support this ground state electron distribution effect. The data in italics show that the relative quantum yields are CN < Cl < CH3 with respect to the electron-donating substituent X, and CN > Cl > CH3 with respect to electron-withdrawing substituent Y. Unfortunately, the different quantities in which the quantum yields are expressed and the different reaction media do not allow a direct comparison of the results. Kobsa s data29 on ortAo-hydroxyphenyl ketone formation in the first column can be correlated with Hammett s a constants (Eq. 1, the fraction is proportional to the quantum yield). 

TABLE 16 Relative Quantum Yields for Fragmentation of 104 in Various Media ]305, 306]... 

TABLE 17 Relative Quantum Yields and t/c Ratios from 97 in Isotropic and Micellar Media 308]... 

Lin and DeMore (637) have irradiated mixtures of 03 and isobutane with monochromatic light of wavelengths from 2750 to 3340 A at —40 C. The bandwidth was 16 A. The relative quantum yields of OCD) production were obtained from the yield of isobutyl alcohol, a product of the reaction 0( D) + isobutane. The results are shown in Fig. VI -13. The quantum yields are constant below 3000 A and show a sharp cutoffat 3080 A, the thermochemical threshold wavelength for the production of O( D) + 02( A). 

The relative quantum yields of the two processes depend on the irradiation wavelength (Table 4.2). 

Electron transfer to the metal centre results in oxidation of the halogen and the complex then dissociates. The relative quantum yields are high (0.1 to 1) when irradiation is made in the GT band in complexes with Br or I this reaction is still observed with irradiation in the d-d bands, but the quantum yields are then lower. 

Figure 7.25 Examples of spectral sensitivities of a photodiode (a) and of two types of photomultipliers (b). The window transmissions are shown as q (silica) and g (optical glass). Horizontal axes, A in nm/100 vertical axes,

This ratio gives the relative quantum yield, or the absolute quantum yield so long as that of the standard is accurate. There are some essential conditions to be met. 

This third primary process produced the hydroxymethyl radical which was needed to explain the third low energy peak in the translational energy distribution curve. From the areas associated with each of the peaks in the translational distribution curves they were able to determine that the relative quantum yields for each of these primary process were 9,4,1, and respectively, for reactions 19, 20, and 21. 

---