Fluorescence absolute quantum yields

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... 

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]. 

Often all three approaches ((1) to (3)) are simultaneously active, e.g., in the dual fluorescence of the classical HCT compounds like DMABN where both the energy of the long-wavelength emission (factor (1)) as well as the ratio between the two bands (factors (2) and (3) above) varies. The simultaneous presence of two bands allows very accurate ratio measuring, and small changes in this ratio can be detected more accurately as if only changes in absolute quantum yields have to be observed. These probes with dual fluorescence will be called type-3. ... 

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). 

The emission lifetimes of the bipy and phen complexes of ruthenlum(II) at 77°K are generally in the range t = 0.5-10 ps. (Table 7). Since these values are intermediate to those generally observed for the fluorescence and phosphorescence of organic compounds, the radiative transition in the ruthenium complexes was suggested to be a heavy-atom perturbed spin-forbidden process (168,169). From a determination of the absolute quantum yields as well as lifetimes of a series of ruthenium(II) and osmium(II) complexes, the associated radiative lifetimes were calculated (170). The variations in these inherent lifetimes within the series could be rationalized with a semi-emipirical spin-orbit coupling model thus affording further evidence that the radiative transitions are formally spin forbidden in these systems. 

HPTS shows a strong fluorescence signal, with an absolute quantum yield close to unity (hence it is a good laser dye). In water at pH=6, R OH fluorescence peaks around 445 nm and is about 1/20 of the R 0 fluorescence signal, which peaks at 510 nm. A steady-state (constant illumination)... 

In order to obtain all the rate constants, and to fully solve the kinetic scheme, one would need to also evaluate the dependence of (f>pc as a function of n, which was established in the 1999 work where the absolute (f>pc and (j)p values for Flindersine were experimentally determined [40]. This led to improved equations to obtain (f>p, particularly because (f>p(n) was considered as the experimentally absolute quantum yield of fluorescence as a function of the vibronic level (n) and state that is excited and ... 

In order to evaluate the photoconductivity energy threshold and the quantum yield the spectral distribution of the light entering the liquid must be known. The relative spectral distribution of VUV-light can be obtained by recording the fluorescence of sodium salicylate deposited on the inside of the entrance window of the conductivity cell. The relative quantum yield of the fluorescence emission spectrum with a peak at 420 nm varies less than 20%, with the incident wavelength between 100 and 160 nm (Samson, 1967). The fluorescence is measured with a photomultiplier. For the determination of the quantum flux, the conductivity cell is filled with a few tens mbar of NO for which the absolute quantum yield for photoionization has been reported (Watanabe et al., 1967). Measurement of the photoelectron emission yield of a gold layer can also be employed (Krolikowski and Spicer, 1970). 

Weber, G., Teale, F.W.J. Determination of the absolute quantum yield of fluorescent solutions. Trans. Farad. Soc. 53, 646-655 (1957)... 

The LIF technique is extremely versatile. The determination of absolute intermediate species concentrations, however, needs either an independent calibration or knowledge of the fluorescence quantum yield, i.e., the ratio of radiative events (detectable fluorescence light) over the sum of all decay processes from the excited quantum state—including predissociation, col-lisional quenching, and energy transfer. This fraction may be quite small (some tenths of a percent, e.g., for the detection of the OH radical in a flame at ambient pressure) and will depend on the local flame composition, pressure, and temperature as well as on the excited electronic state and ro-vibronic level. Short-pulse techniques with picosecond lasers enable direct determination of the quantum yield [14] and permit study of the relevant energy transfer processes [17-20]. 

Chiral dendrimers based on oligonaphthyl cores and Fr chet-type poly(aryl ether) dendrons have been investigated [44]. The absolute configuration of these dendrimers remains the same as that of their chiral cores. Both the nature of the core and the generation play a role in determining the fluorescence quantum yield. 

Figure 7. Dependence of the fluorescence quamum yield of BMPC on solvent viscosity ( ) in linear alcohols, from methanol to dccanol, at 25°C, (o) in absolute ethanol between 200 and 298 K. The quantum yields were measured on optically thin samples (Am <0.2). The value in ethanol, 5.7x10, was determined relative to quinine sulfate in 0.5 mol 1" HjSO ((j)p=0.55 [62]) and 9,10-diphenylanthracene in cyclohexane (4ip=0.90 [63]). It was then used as a reference for the determinations in the other alcohols.

S. Hamai and F. Hirayama, Actinometric determination of absolute fluorescence quantum yields, J. Phys. Chem., 87 83-89, 1983. 

Collection of multiple data sets for each time span, with frequent alternation of the polarization, is an essential feature of our protocol. This provides some protection against the effects of drifts in laser power, photomultiplier quantum yield, and absolute calibration of the TAC, photochemical decomposition of the dye, and any other long-term processes that may alter the measured fluorescence response curves. Separate analysis of each data set is necessary to provide an indication of the uncertainty in run-to-run reproducibility and to detect and delete the rare spurious data set. 

Fig. 7 Selected 2PA spectra obtained by absolute fluorescence-based methods, a Spectra for fluorescein, rhodamine B, coumarin 307, and , -p-bis(o-methylstyryl)benzene (the solvent is indicated in the legend) obtained by Xu and Webb [78]. In the case of coumarin 307, the ordinate displays the quantity rjSy where rj is the fluorescence quantum yield, b Spectrum for , -p-bis(o-methylstyryl)benzene (this spectrum is obtained from the tabulated values for the band shape reported by Kennedy and Lytle [90] and the cross section at 585 nm reported by Fisher et al. [80], to correct for a typographical error in the 1986 paper). Part (a) reproduced with permission from [78]. 1996, Optical Society of America...

Despite the nearly identical absorption spectra of both polymers, the emission quantum yield of poly(dA) is nearly three times that of poly(A), as can be seen from the unsealed emission spectra (Fig. 1) measured from polymer solutions having identical absorbance at the excitation wavelength of 280 lim. The absolute fluorescence quantum yield of poly(A) has previously been reported as 3 x 10 [16]. Interestingly, the situation is reversed at 77 K, and more fluorescence was reported from the ribo- than from the deoxyribopolymer [15]. The... 

This type of kinetic situation sometimes occurs in protein renaturation experiments, in which the kinetics are often monitored by fluorescence changes. The biphasic traces cannot be resolved in such circumstances unless the quantum yield of the transient intermediate is known, so that its absolute concentration can be determined. 

---