Fluorescence quantum yield values

Table 7.16 Fluorescence Spectroscopy of Some Organic Compounds Table 7.17 Fluorescence Quantum Yield Values...

Emission spectra have been recorded for four aryl-substituted isoindoles rmder conditions of electrochemical stimulation. Electrochemiluminescence, which was easily visible in daylight, was measured at a concentration of 2-10 mM of emitter in V jV-dimethylformamide with platinum electrodes. Emission spectra due to electrochemi-luminescence and to fluorescence were found to be identical, and quantum yields for fluorescence were obtained by irradiation with a calibrated Hght source. Values are given in Table X. As with peak potentials determined by cyclic voltammetry, the results of luminescence studies are interpreted in terms of radical ion intermediates. ... 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

Solid-surface fluorescence and phosphorescence quantum yield values were obtained from +23° to -180°C for the anion of p-aminobenzoic acid adsorbed on sodium acetate (11). Fhosphorescence lifetime values were also obtained for the adsorbed anion from +23° to -196°C. Table 1 gives the fluorescence and phosphorescence quantum yield values acquired. The fluorescence quantum yield values remained practically constant as a function of temperature. However, the phosphorescence quantum yield values changed substantially with temperature. The phosphorescence lifetime experiments indicated two decaying components. Each component showed a gradual increase in phosphorescence lifetime with cooler temperatures, but then the increase appeared to level off at the coldest temperatures. 

Table I. Fluorescence and Phosphorescence Quantum Yield Values for the Anion of p-Aminobenzoic Acid Adsorbed on Sodium...

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 ... 

For the photodiagnostic use of these compounds, a high quantum yield of fluorescence, r, is desirable. The metal complexes of the common first-row transition metals are not suitable, because they show very low 4>f values. On the other hand, porphyrin complexes of d° and d10 elements show appreciable fluorescence, although generally less than that of the metal-free compounds, presumably because of the heavy-atom effect (e.g., TPP ZnTPP, Table 5). The further operation of the heavy-atom effect, which increases the rate of intersystem crossing (/cisc) by... 

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]. 

Thus, the greater the numbers or rates of processes competing with fluorescence for deactivation of the lowest excited singlet state, the lower the value of <()/. The quantum yield of fluorescence is important in determining how intense chemiluminescence can be for a particular reaction. 

The quantum yield values (<)>fnp) are corrected for the absorption of the excitation light by the non-fluorescent, planar component using Equation 2. 

The value of the quantum yield of fluorescence of TIN in the PMMA film (calculated using the total film absorbance at the excitation wavelength) decreases from 1.2 x 10-3 to 5.0 x 10"4 when the concentration of TIN is increased from 0.07 mole% to 5.0 mole%. This suggests that the TIN molecules are involved in a concentration-dependent, self-quenching process. 

Using the values of quantum yields and fluorescence lifetime, rate constants on the state were obtained. The results are summarized in "Table III". As seen in "Table III", no isotope effect is observed in the rate constants for the fluorescence and intersystem crossing. On the other hand, in the case of TPP the rate constants of internal conversion show a large isotope effect that of D2TPP is... 

The quantum yield of fluorescence from 3130-A excitation of gaseous acetone has been measured as 0.002,308 whereas a value of 0.01 has been measured in solution.316 If the rate of fluorescence, as calculated from the integrated absorbance intensity, is 4 x 10 sec-1,316 the rate of intersystem crossing of singlet acetone lies between 4 x 107 and 2 x 108 sec-1. 

In presence of dissolved oxygen, photooxidation may also occur. Bowen and Williams (19) carried out some early experiments with benzene, some of its methyl derivatives, and certain other aromatic hydrocarbons in hexane solutions illuminated with light at 2537 A. They found low values for the quantum yields of fluorescence and of oxygen take-up the sum of these quantities being less than unity. At higher temperatures (>50°C.) chain propagation by a radical mechanism... 

Experimental data show that, at temperatures from about 100 to about 200 °C, co 1 at wavelengths from 2500 to 3200 A50,51. The value cannot be exactly unity toward the long wave end of this region because there is a small fluorescence of acetone even at these temperatures52. The exact point at which fluorescence ceases to be excited is indeterminate and should be slightly temperature dependent. There is no fluorescence at 2537 A. The quantum yield of fluorescence seems never to have been determined with high precision, partly because it is low and the intensity very weak. The value is certainly less than 0.01 under the experimental conditions cited. Hence within the experimental error one may state... 

The quantum yields of fluorescence of the different systems have also been determined relative to a single crystal of neodymium-doped YAG for which a quantum yield of unity has been assumed (Heller, 1968a). The quantum yields obtained, even if they are accurate only within a factor of two, follow the same trend as for the lifetimes, with the highest values for the acidic solutions 0.70 and >0.75 in presence of S11CI4 and SbCls, respectively. Neutral and basic solutions are less luminescent and have quantum yields of 0.5 and 0.4, respectively. Identical measurements performed on a sodium-compensated neodymium-doped calcium tungstate crystal lead to a value of 0.5. The high quantum efficiency and the low threshold (between 2 and 40 J) of these Nd3+ SeOCl2 systems clearly demonstrate that liquids are not inherently inferior to solids as laser materials. 

Fig. 1 Fluorescence characteristics of photosynthesis determined over the day for iron-limited (open symbols) and iron-replete cells (closed symbols), plotted alongside irradiance (photons m 2 s dashed line). Fluorescence dynamics are expressed in percentages, taking the maximum morning values as reference (i.e. 100% n = 3). (A) Maximum quantum yield of fluorescence (Fv/Fm). (B) Minimum fluorescence (/< ). (C) Maximum fluorescence (Fm)...

Energy-dependent (but not state-dependent) lifetime and quantum yield data are available for some of the more complex carbonyls. With reference to those molecules for which the appropriate data do exist, it can be seen in Table 11 that the radiative lifetime is virtually unaffected over a wide range of energies. This is in sharp contrast to the observed behavior of formaldehyde. The tr values for acetone might be less reliable than the others listed they are calculated using the fluorescence lifetime data of Breuer and Lee (42) and the fluorescence quantum yield data of Heicklen (105). It can be seen that there is no substantial change in tr the apparent (perhaps the real) trend is in the direction opposite that observed for formaldehyde. The values for perfluorocyclobutanone have been calculated using the rp and relative quantum yield values of Lewis and Lee (141) and the absolute fluorescence yield of 0.021 as measured by Phillips (187) as a standard. 

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