Molar absorption coefficient at the excitation

In spectrofluorometry, Y is the fluorescence intensity IF(AE,AF) of the solution for a couple of excitation and observation wavelengths, a and b are proportional to the molar absorption coefficients (at the excitation wavelength) and the fluorescence quantum yields of A and B, respectively. 

Brightness. Brighmess of a fluorophore is proportional to the product of the molar absorption coefficient at the excitation wavelength times its quantum yield. This is the theoretical value, but in practice it can be much reduced by fluorescent quenching on interaction with other labels on the protein or DNA surfaces. Sulfonic acid groups on the aromatic rings of cyanines reduce this interaction, giving very much improved protein fluorescence. 

Both the absolute quantum yield (determined with respect to zinc tctraphcny 1 porphvrin in ethanol) and the product of the molar absorption coefficient at the excitation wavelength with the quantum yield, e Q, which represents the overall luminescence efficiency follow the... 

Another method of calculating the FRET efficiency is via the change in the fluorescence intensity of the acceptor. This method is based on Eq. 9, where D( exc) and EaC cxc) are the donor and acceptor molar absorption coefficients at the excitation wavelength. A large variety of other mathematical formulas have been developed to calculate FRET efficiency in many different... 

This ratio is called the photostationary state composition. In the photostationary state, the rate of formation of each isomer from the nonvertical excited state is equal to its rate of removal by absorption of light. There is a roughly equal probability of the relaxation of the nonvertical excited state forming either the cis or the trans isomer and so the main factor influencing the photostationary state composition is the competition for absorbing light. This will, of course, depend on the relative values of the molar absorption coefficients of the two isomers at the particular wavelength chosen. 

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). 

These are commonly observed in transient absorption spec troscopy, and make it difficult to analyze one-photon photoprocesses of polymers. An exceptional case involves studies on polymers having carbonyl groups reported by Schnabel et al. (42). No distinct contribution of intrapolymer S2 -Si annihilation was observed, which was ascribed to a small value of the molar extinction coefficient at the laser wavelength and to fast intersystem crossing. Simultaneous as well as successive two-photon processes might be suppressed compared to one-photon processes. On the other hand, studies on primary photoprocesses of polymers with pendant aromatic groups can be performed only by examining excitation intensity effects in detail. This has been demonstrated clearly not only by our experiments described here, but also by recent reports by Webber et al. (43). 

In the cell shown in Fig. 9.13 [20] WE is a Pt disk which is placed at a distance of 25-200 pm from the surface of the optical window to speed up electrolysis (1-100 s). The excitation light, sent by means of the optical fibre, encounters the quartz window with an angle of 45°, while the emission light is collected perpendicular to this window by means of another optical fibre. This kind of cell enables to measure the emission in spectroelectrochemical experiments performed on very diluted solutions (5 pM), one order of magnitude lower than the minimum concentration that can be detected in absorption with the same cell and the same electroactive species. This result clearly evidences the higher sensitivity of the emission measurements compared to the absorption ones. Obviously the sensitivity of the spectroelectrochemical experiments coupled to absorption or emission measurements depends on the molar absorption coefficient and the quantum yield, respectively, of the examined species. 

Hence the quantity of EA can be simply calculated from the corrected sensitized emission image and the acceptor only image provided the ratio of the molar extinction coefficients of the donor and acceptor at the donor excitation wavelength is known (ct). This quantity can be determined from absorption spectra of purified labeled components or can be experimentally determined as follows. First, let us define a factor v that relates the signal of N acceptors in the S channel to the signal of the same number of donors in the D channel ... 

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