Relative fluorescence quantum yield

We see then that the relative fluorescence quantum yield can be determined by measuring the areas under the fluorescence bands of the sample and the fluorescent standard. However, these spectra must be corrected before their true areas can be determined. Several factors are responsible for this. The most important of these are the phototube and monochromator responses. For most phototubes the maximum response occurs within a limited wavelength range, falling off rather sharply in some cases at the short-and long-wavelength ends. This is illustrated in Figure 2.14. Similarly,... 

If pK is greater than 2, a plateau is observed for the relative fluorescence quantum yield of the acidic form and the basic form for pH ranging from pK to pK (Figure 4.10A) because of the absence of diffusional recombination. In fact, Eqs (4.59) and (4.60) which are relevant to this case show that /HA and IA- are constants. A typical example is 2-naphthol (pK = 9.3, pK = 2.8). 

Fig. 4.10. Variations in relative fluorescence quantum yields of acidic and basic forms versus pH for various cases.

Table 7.3. Relative Fluorescence Quantum Yield of Crystal Violet,

Methods for the measurement of absolute quantum yields have been reviewed. 6 In most steady-state fluorescence experiments relative fluorescence quantum yields are determined by comparison with appropriate standards (see Section 7.7.1.2.1). 

Another interesting observation is that at room temperature (small viscosity condition) and for the different alcoholic solutions (where the B emission due to the backward reaction B <— A is negligible), a straight line with slope very close to unity has been found (Fig. 5.5) for the curve log versus log 17, where is the relative fluorescence quantum yield of the B state deduced from stationary spectra with B = 1 in cyclohexane. 

The excited-state dynamics of the 2-hydroxypheylbenzotriazole (HPB) photostabilizer copolymerized with polystyrene (51) are reported in Ref. 195. The HPB fluorescence from these copolymer films is observed at 630 nm, characteristics of the proton-transferred excited state of HPB, and it has a rise time of < 10 psec and a decay time of 28 4 psec at room temperature. Measurement of the relative fluorescence quantum yield as a function of temperature gives the activation energy for nonradiative decay of this state as 259 25 cm-1. 

It is less than the fluorescence in the absence of quenchers F(0) = AIoNx. The ratio F(c)/F(0) is known as a relative fluorescence quantum yield ... 

The relative fluorescence quantum yield defined in Eq. (3.8) is the ratio of the stationary singlet excitation concentration in the presence of quenchers to the same concentration in their absence. By substituting into this definition N from Eq. (3.654a), we confirm that the fluorescence quantum yield obeys the Stem-Volmer law (3.363) with the same constant as in Eq. (3.364), but with the contact [Pg.339]

Porphyrins with quinones attached (Figure 7.13) show a marked decrease in their singlet excited state lifetimes for example, from nanoseconds to picoseconds. The relative fluorescence quantum yield (i.e. the ratio of the number of molecules fluorescing to the number of light quanta absorbed— a difficult number to obtain absolutely) also drops, from 0.1 in the case of an unquenched mcso-tetraarylporphyrin, to 10" for the porphyrin tetraquinone in which the quinones are directly bonded to the macrocyclic mcso-positions. As soon as the electron is excited, it is transferred to the quinone electron acceptor. This effectively depopulates the porphyrin singlet excited state, which is observed as a reduction in intensity and a blue shift of the porphyrin B band. Subsequently many workers have expanded on this theme. ... 

Fig. 12. Relative fluorescence quantum yields of benzene vapor at 300 K as a function of exciting wave. Those data indicated by squares are normalized to the point at 2536 A and arc from excitation with lines from a mercury arc. Those data indicated by circles are from another set obtained with light from a Xe arc coupled with a monochromator whose bandpa.ss is about 6-15 A. They are normalized to the average in that set between 2530 and 2590 A. The two sets are independent and not normalized to each other. All quantum yields are obtained from mixtures of benzene and cyclohexane with benzene pressures in the range 0.5 to 3 torr and cyclohexane between 35 and 50 torr. Data from Noyes and Harter.

The fluorescent dyes and pigments have to have high fluorescence quantum yields in thin gel films for application to optical display. Absolute fluorescence quantum yields of dyes and pigments in gel films co d not be measured, because there is lack of a standard reference and interaction between fluorescent dyes and matrix gel is significantly dependent on alkoxysilanes used, and aggregation of fluorescent dyes and pigments occurs. Relative fluorescence quantum yield (Q,/) of fluorescent colorants 12-17 in EtOH and in thin gel film are summarized in Table 28-2 (Nakazumi, 1997a). Most of fluorescent colorants used... 

TABLE 28-2. RELATIVE FLUORESCENCE QUANTUM YIELD (Of) FOR ORGANIC DYES AND PIGMENTS IN EtoH AND IN GEL FILM PREPARED FROM MTSO... 

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