And quantum yield

Sun Y-P, Wang P and Hamilton N B 1993 Fluorescence spectra and quantum yields of Buckminsterfullerene (Cgg) in room-temperature solutions. No excitation wavelength dependence J. Am. Chem. Soc. 115 6378-81... 

Fig. 13.11. A schematic drawing of the potential energy surfaces for the photochemical reactions of stilbene. Approximate branching ratios and quantum yields for the important processes are indicated. In this figure, the ground- and excited-state barrier heights are drawn to scale representing the best available values, as are the relative energies of the ground states of Z- and E -stilbene 4a,4b-dihydrophenanthrene (DHP). [Reproduced from R. J. Sension, S. T. Repinec, A. Z. Szarka, and R. M. Hochstrasser, J. Chem. Phys. 98 6291 (1993) by permission of the American Institute of Physics.]...

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. ... 

The first term in Eq. (7.7) is the in-phasc signal, which has the same phase as that of the pump, and the second term is a quadrature or out-of-phase signal, which has a 90° phase relative to that of the pump. Their respective frequency dependencies are shown in Figure 7-2. The normalized change in transmission can be related to the excitation cross-section and quantum yield of generation ... 

Fig. 3.1.5 Effects of salt concentration on the activity of Cypridina luciferase (solid lines) and quantum yield (dotted lines). In the activity measurement, Cypridina luciferin (1 pg/ml) was luminesced with a trace amount of luciferase in 2.5 mM HEPES buffer, pH 7.5, containing a salt to be tested, at 20°C. In the measurement of quantum yield, luciferin (1 pg/ml) was luminesced with luciferase (20 pg/ml) in 20 mM sodium phosphate buffer (for the NaCl data) or MES buffer (for the CaCl2 data), pH 6.7.

Quantum yield of coelenterazine. The quantum yields of coelenterazine in the luminescence reaction catalyzed by luciferases A, B and C are all close to 0.30 at 24°C, which is one of the highest values among coelenterazine luciferases. The amount of luciferase L obtained was insufficient to measure reliable data of specific activity and quantum yield. 

Seliger, H. H., and McElroy, W. D. (1960). Spectral emission and quantum yield of firefly bioluminescence. Arch. Biochem. Biophys. 88 136-141. 

Ward, W. W., and Seliger, H. H. (1976). Action spectrum and quantum yield for the photoinactvation of mnemiopsin, a bioluminescent photoprotein from the ctenophore Mnemiopsis sp. Photochem. Photobiol. 23 351-363. 

The electron transfer step is typically fast and efficient. Griller et a/.292 measured absolute rate constants for decay of benzophenone triplet in the presence of aliphatic tertiary amines in benzene as solvent. Values lie in die range 3-4x109 M 1 s 1 and quantum yields are close to unity. 

Becker et al. (1977b summary Becker, 1978) measured rates and quantum yields for the photolysis of benzenediazonium tetrafluoroborate under various conditions (additives, quenchers, etc.) in methanol. 

FPY and FQY—See Fluorescence photon and quantum yield Free energy of extraction of Am(III) by carbamoylmethylphosphoryl... 

Table 4. Photolysis constants (k) and Quantum Yields (O) of Brominated Dibenzodioxins and furans in n-Hexane as Solvent. A and B are replicates. 

Between 1923 and 1927, the concepts of quantum efficiency (number of photons emitted divided by number of photons absorbed by a sample) and quantum yield (fraction of excited molecules that emit) had been defined and values determined for many compounds by Vavilov (34). The quantum yield indicates the extent that other energy loss mechanisms compete with emission in an excited molecule. Although the quantum yield is influenced by the molecular environment of the emitter, for a given environment it depends on the nature of the emitting compound and is independent of concentration and excitation wavelength, at least at low concentrations (35). Tlius, it serves as another measurable parameter that can be used to identify the compounds in a sample and also, because of its sensitivity to the surroundings of the luminophore, to probe the environment of the emitter. 

Gaunt, J. A. Knight, A. E. Windsor, S. A. and Chechik, V. (2005). Stability and quantum yield effects of small molecules additives on solutions of semiconductor nanoparticles. /. Colloid and Interface Science, 290 (2), 437-443. 

The validity of the above conclusions rests on the reliability of theoretical predictions on excited state barriers as low as 1-2 kcal mol . Of course, this required as accurate an experimental check as possible with reference to both the solvent viscosity effects, completely disregarded by theory, and the dielectric solvent effects. As for the photoisomerization dynamics, the needed information was derived from measurements of fluorescence lifetimes (x) and quantum yields (dielectric constant, where extensive formation of ion pairs may occur [60], the observed photophysical properties are confidently referable to the unperturbed BMPC cation. Figure 6 shows the temperature dependence of the... 

Fig. 26. Concentration of radical anions immediately after the laser flash and quantum yield as functions of the concentration of the respective sodium halide...

A tetrameric structure with the Zn40 core can also be formed with the 7-azaindolate ligand, [Zn40(C7H5N2)6], and has been structurally characterized. The tetramer displays intense photoluminescence at 448 nm in the solid state and 425 nm in acetonitrile with a lifetime and quantum yield of 0.1 ps and 0.17 ps respectively.280... 

However, it has been pointed out 13 16> for large organic molecules ( statistical limit case) that the decay times and quantum yields can legitimately be handled by the Fermi golden rule ... 

PHOTOCHEMICAL KINETICS CONCENTRATIONS, RATES, YIELDS, AND QUANTUM YIELDS For a molecule A undergoing light absorption and reaction in its lowest excited singlet state to form a product P, we can write the following hypothetical mechanism, where A and Af are the lowest excited singlet and triplet states, respectively ... 

Photophysical and Photochemical Pathways, and Quantum Yields (< ) of P-Carotene and Canthaxanthin in Deaerated Toluene Solution at 25°C... 

It can be seen that the ratio of concentrations of free and occupied receptors is determined not only by xF and aB values but also by correspondent lifetimes and T and the products of molar absorbances sF or sB and quantum yields dip or Ob. 

The dihydroxyaniline-squaraine chromophore was used by Akkaya and Isgor in the fluorescent chemosensor 30 for the measurement of pH [90]. This chemosensor, having the molar absorptivity about 200,000 M em 1 and quantum yield 0.2,... 

AT1 cm ). and therefore, these dyes are excitable not only with red (635 or 670-nm) but also with blue (380, 405, and 470 nm) diode lasers or LEDs (Fig. 1). Carbonyl containing substituents such as 1,3-indanedione, cyanoacetic ester, barbituric, and thiobarbituric acid form intramolecular H-bond with the polymethine hydrogens of the squaraine bridge. As a result, the molar absorptivities and quantum yields of these dyes are substantially decreased. 

Square-650-pH having a pKa in the physiological pH range (pKa = 7.1 for free dye and the pKa 6.1 when labeled to an antibody) was recently introduced by SETA BioMedicals [119]. This dye is commercially available as a free carboxylic acid and a mono-NHS ester. Square-650-pH has spectral properties similar to those of the CypHer dyes but is fluorescent in both the protonated and deproto-nated forms. This dye displays reasonable molar absorptivities (135,000 and 48,000 M-1cm-1) and quantum yields (16% and 9%) for the protonated and deprotonated forms, an extremely large Stokes shift of more than 100 nm for the deprotonated form, and enables excitation and emission ratiometric measurement... 

The experiment is performed with a spectrofluorometer similar to the ones used for linear fluorescence and quantum yield measurements (Sect. 2.1). The excitation, instead of a regular lamp, is done using femtosecond pulses, and the detector (usually a photomultiplier tube or an avalanche photodiode) must either have a very low dark current (usually true for UV-VIS detectors but not for the NIR), or to be gated at the laser repetition rate. Figure 11 shows a simplified schematic for the 2PF technique. 

Fig. 4 Combinatorial synthesis of coumarin library using Pd-mediated cross-coupling reaction and 3D scatter plot of representative coumarin derivatives according to their excitation, emission wavelength, and quantum yield. All the photophysical properties were measured in ethanol...

The measurement of fluorescent decay dynamics, i.e., fluorescence lifetime measurements, promise to overcome several of the challenges discussed above. Most importantly, lifetime and quantum yield are directly related through (11),... 

Table 8 Peak positions (AF) and quantum yields (<1>F) of fluorescence of bithiophene derivatives...

Flowever, there is a trade-off in using near-IR emissive lanthanides, in that luminescence lifetimes are shorter, and quantum yields lower, compared to complexes of Tb and Eu. This arises because the near-IR emissive lanthanides are quenched by lower harmonics of the O-H oscillator, increasing the Franck-Condon overlap with the metal excited state. For neodymium, matters are further complicated by the manifold of available metal-centered excited states, which leads to particularly effective quenching by C-H oscillators. Thus, complexes in which there are few C-H oscillators close to the metal are desirable if the luminescence lifetime is to be optimized (e.g. 44).76 97-101... 

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