Fluorescent quantum yield

Similar to the fullerene ground state the singlet and triplet excited state properties of the carbon network are best discussed with respect to the tliree-dimensional symmetry. SurjDrisingly, the singlet excited state gives rise to a low emission fluorescence quantum yield of 1.0 x 10 [143]. Despite the highly constrained carbon network,... 

Table 7.16 Fluorescence Spectroscopy of Some Organic Compounds Table 7.17 Fluorescence Quantum Yield Values...

Accuracy The accuracy of a fluorescence method is generally 1-5% when spectral and chemical interferences are insignificant. Accuracy is limited by the same types of problems affecting other spectroscopic methods. In addition, accuracy is affected by interferences influencing the fluorescent quantum yield. The accuracy of phosphorescence is somewhat greater than that for fluorescence. 

Table 7.11 Fluorescence quantum yield

One characteristic property of dyes is their colour due to absorption from the ground electronic state Sq to the first excited singlet state Sj lying in the visible region. Also typical of a dye is a high absorbing power characterized by a value of the oscillator strength/ (see Equation 2.18) close to 1, and also a value of the fluorescence quantum yield (see Equation 7.135) close to 1. 

A substantial effort has been appHed to iacreaskig i by stmctural modification (114), eg, the phthalaziQe-l,4-diones (33) and (34) which have chemiluminescence quantum yields substantially higher than luminol (115,116). The fluorescence quantum yield of the dicarboxylate product from (34) is 14%, and the yield of singlet excited state is calculated to be 50% (116). Substitution of the 3-amino group of lumiaol reduces the CL efficiency > 10 — fold, whereas the opposite effect occurs with the 4-amino isomer (117). A series of pyridopyridaziae derivatives (35) have been synthesized and shown to be more efficient than luminol (118). 

The effect of forming a more rigid structure in fluorescent dyes of the rhodamine series has been clearly demonstrated (18) with the remarkable dye designated Rhodamine 101 [41175A3-3] (19). This dye has its terminal nitrogen atoms each held in two rings and has a fluorescence quantum yield of virtually 100% independent of the temperature. 

Properties of luciferin. The crystals are microscopic needles, which melt with decomposition at 205-210°C (Bitler and McElroy, 1957). It is a quite stable luciferin compared with some other luciferins, such as Cypridina luciferin and the luciferins of krill and dinoflagellates. It is not significantly affected by lOmM H2SO4 and lOmM NaOH at room temperature in air. The absorption spectral data of luciferin are shown in Fig. 1.3 (McElroy and Seliger, 1961). The molar absorption coefficient of the 328 nm peak in acidic solutions and that of the 384 nm peak in basic solutions are both 18,200 (Morton et al., 1969). Luciferin is fluorescent, showing an emission maximum at 537 nm in both acidic and basic conditions, although the intensity of the fluorescence is lower in acidic solution than in basic solution (fluorescence quantum yields 0.62 in basic condition, and 0.25 in acidic condition Morton et al., 1969). The chemical synthesis... 

Fluorescence emission maximum Fluorescence quantum yield Molar absorption coefficient (e) at peak wavelengths (as monomer)... 

Lei, B., Ding, Q., and Tu, S.-C. (2004). Identity of the emitter in the bacterial luciferase luminescence reaction binding and fluorescence quantum yield studies of 5-decyl-4a-hydroxy-4a,5-dihydroriboflavin-5 -phosphate as a model. Biochemistry 43 15975-15982. 

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Non-Radiative Decay Channels - 1064 nm Excitation. We turn now to a comparison of the observed fluorescence photon yield defined by Equation 1 and the expected fluorescence quantum yield of the 4550 cm 1 state which indicates that several non-radiative decay channels may be open following 1064 nm excitation of PuF6(g) The following relationship between... 

Figure 3. Energy diagram for 1064 nm excitation of PuFg(g). The 5f electron states of PuF6 are shown at the left. The solid arrows Indicate photon absorption or emission processes. The wavy arrows indicate nonradiative processes by which excited states of PuF6 are lost. Comparison of observed fluorescence photon yields versus the fluorescence quantum yield expected for the 4550 cm" state indicate that the PuFg state initially populated following 1064 nm excitation may dissociate as shown.

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

Solid-surface fluorescence and phosphorescence quantum yield values were obtained from +23° to -180°C for the anion of p-aminobenzoic acid adsorbed on sodium acetate (11). Fhosphorescence lifetime values were also obtained for the adsorbed anion from +23° to -196°C. Table 1 gives the fluorescence and phosphorescence quantum yield values acquired. The fluorescence quantum yield values remained practically constant as a function of temperature. However, the phosphorescence quantum yield values changed substantially with temperature. The phosphorescence lifetime experiments indicated two decaying components. Each component showed a gradual increase in phosphorescence lifetime with cooler temperatures, but then the increase appeared to level off at the coldest temperatures. 

Temperature ( C) Fluorescence quantum yield, Phosphorescence quantum yield,... 

Figure 4. Graphs of fluorescence quantum yield and phosphorescence quantum yield ( ) versus log of the ratio of millimoles of dissolved sodium acetate to millimoles of p-aminobenzoic acid anion. (Reproduced from reference 12. Copyright 1988 American Chemical Society.)...

The fluorescent signal will change with variation in quantum yield of fluorescence and with molar absorptivity. Not only do fluorescence quantum yields vary with the different dansyl derivatives formed, but so do the molar absorptivities (12). Another problem is exemplified by the 30-nm difference in the emission maxima of the dansyl derivatives of phenol and 2,4,5-trichlorophenol (13). 

R n Compound Number Molar Absorptivity, e X iq3 Fluorescence Quantum Yield, 4> Wavelength of Maximum Absorbance, A. (nm) max... 

R ( ) Fluorescence Quantum. Yield, (t> Molar Absorptivity, e X 10 Wavelength Maximum Ahsorhance, A max (nm) Emission, em... 

Quimtua Yields of Fluorescence Measurements. All of the quantum yields of fluorescence were measured by the relative fluorescence measurement technique of Parker and Rees (24). This method compares the fluorescence of the compound of interest to the fluorescence of some known compound. All of the fluorescence quantum yields were measured using I as a reference. Compound I had previously been measured by this same method using rhodamine B as a standard. 

In the equation, the subscripts 1 and 2 refer to the reference compound and the compound of interest, respectively, is the intensity of the fluorescent signal of each compound measured as peak height in centimeters, 8 is the molar absorptivity, c is the concentration in moles per liter, and is the fluorescence quantum yield. In this application, i is set at 1.00. The concentrations of the solutions that were tested ranged from 10 to 10 M. The solutions run at the higher concentrations were all checked for self-quenching, but none was found. All measurements, except the fluorescence-versus-solvent study, were made in 0.1-N phosphate buffer, pH 7.4. Slit settings on the Perkin-Elmer MPF-2A were 10 mp (nm) for both emission and excitation monochromators. 

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