Quantum yields emission

The significant enhancement in emission quantum yields and lifetimes suggests that 3 can be used as a noncovalent probe in immunochemical assay and biophysical studies. This dye is quite soluble in aqueous buffer and interacts with... 

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. 

Several luminescent ( 650 nm) dioxorhenium(V) systems(25) have been investigated as potential 0-atom transfer agents. The emission quantum yields measured with 436 nm excitation are about 0.03 for trans-ReO (pyridine)u and its isotopically-substituted derivatives in pyridine solution. The excited state lifetimes of these ions vary from 4 to 17 ys. 

Experimentally, Eem is available from the emission spectrum and knr from a combination of excited state lifetime (x0) and emission quantum yield (<(>r) measurements as shown in eq. 15. An... 

Most commonly absorption or fluorescence spectroscopy is used for detection of the changes in the concentration of G or HG. The monitoring wavelength is chosen so that the difference between the molar absorptivities, in case of absorption, or emission quantum yields, in the case of fluorescence detection, between G and HG is maximized. The amplitude of the relaxation process depends on the difference in the molar absorptivities or fluorescence quantum yields, but the observed rate constants are the same at all observation wavelengths when the kinetics are first- or pseudo-first order (Fig. 3). 

Kinetics with positive and negative amplitudes were observed for the natural ml-DNA and bm-DNA samples binding to 5.119 The kinetics were monitored by the fluorescence of 5 and the emission quantum yield for 5 bound to GC sites was much lower than for 5 bound to AT sites. The positive amplitudes were related to relocation of 5 from GC sites to AT sites. The different kinetics observed for ml-DNA compared with bm-DNA are in line with the observation that the binding dynamics of 5 with poly[d(G-C)] and poly[d(A-T)] were very different. 

The ruthenium(II) polypyridyl complexes are also popular but the brightnesses do not exceed 15,000 and thermal quenching is rather significant. This property can be utilized to design temperature-sensitive probes providing that the dyes are effectively shielded from oxygen (e.g., in polyacrylonitrile beads). Despite often very high emission quantum yields the visible absorption of cyclometallated complexes of iridium(III) and platinum(II) is usually poor (e < 10,000 M-1cm-1), thus,... 

Bunz et al. pointed out that it would be of interest to develop materials that combine the stability, electron affinity, and high emissive quantum yield of PPEs with the excellent hole injection capabilities of poly(p-phenylene vinylene)s (PPVs) [48]. In line with this notion,recent synthetic activities have focused on the engineering of the band gap, conduction band, and valence band of PAEs with the objective to render these materials more useful for practical applications that exploit their electrically (semi)conducting nature. Examples of materials that emerged from these efforts are discussed in detail in other portions of this volume (in particular the chapters by Bunz, Klemm, and Yamamoto). They include, among others, poly(heteroarylene ethynylenes) such... 

An apparent decrease in the emission quantum yield and/or distortion of the band shape due to the reabsorption of emitted radiation. If such an effect is not corrected or compensated for, results of an emission experiment may prove to be incorrect. This is especially true in fluorescence quenching experiments conducted to evaluate the stoichiometry and affinity of ligand binding. 2. In a light irradiation experiment, the absorption of incident radiation by a species or molecular entity other than the intended primary absorber. See Fluorescence... 

The physicochemical parameters commonly determined in mechanistic CL research are the rate constants, the activation parameters and the CL emission quantum yields (cl). as well as the electronic excitation yields (< > ), which can be singlet (4>s) or triplet... 

The kinetics of CL reactions can most conveniently be followed by measuring the time course of the emission intensity. The emission intensity at any time of the reaction corresponds to the velocity of excited-state formation and therefore to the velocity of the excitation step (electronic transitions and energy transfer processes should certainly be faster than the excitation step ). Therefore, the emission intensity fm) is determined by the rate constant of the excitation step (kex), the concentration of the HEI and, in the case of activated CL, the concentration of the ACT, as well as the < > and the emission quantum yield of the emitting species ([Pg.1221]

Emergency Response Guidebook, 747 Emission quantum yields, chemiluminescence, 1221, 1222-3... 

Nevertheless, the example 17 has been available since 1989. This was the first case where all the optical and ion-binding parameters of a functioning device were quantitatively predictable from model compounds within experimental error. The only exception was the emission quantum yield of the switched- on state which deviated negatively by 30%. Part of this deviation was caused by the different solvent conditions which were necessary for examining the model lumophore. This was an illustration of rather exact molecular engineering since the specifications at... 

Returning to Fig. 10, because the majority of the alkyl groups are flexible and because the interfacial electrostatic binding geometries are unknown, the rate of falloff of kbET or Hab with semiconductor/molecule separation distance cannot be evaluated quantitatively. A curious finding that remains unexplained is that the falloff with osmium complexes is considerably weaker than with ruthenium species. Finally, although the injection reaction was not the focus of the study, spacers clearly do decrease its rate, as shown, for example, by an increase in emission quantum yield (decrease in injection efficiency) with the largest spacers. 

Excitation-wavelength-dependent emission polarization studies indicate the presence of an overlapping xy polarized transition in the bluer part of the 290-315-nm range, as indicated in Fig. 5. The combination of static absorption, time-resolved emission, and emission quantum yield measurements suggests that the emitting state has the same polarization (z axis, linear), but is not the same state as that giving rise to the 362-nm absorption peak. These assignments for the 3.5-nm particles are summarized in Fig. 5. 

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... 

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