Quantum fluorescence

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,... 

Nonradiative reiaxation and quenching processes wiii aiso affect the quantum yieid of fluorescence, ( )p = /cj /(/cj + Rsiative measurements of fluorescence quantum yieid at different quencher concentrations are easiiy made in steady state measurements absoiute measurements (to detemrine /cpjj ) are most easiiy obtained by comparisons of steady state fluorescence intensity with a fluorescence standard. The usefuiness of this situation for transient studies... 

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

The fluorescent emission for quinine at 450 nm can be induced using an excitation frequency of either 250 nm or 350 nm. The fluorescent quantum efficiency is known to be the same for either excitation wavelength, and the UV absorption spectrum shows that 250 is greater than 350- Nevertheless, fluorescent emission intensity is greater when using 350 nm as the excitation wavelength. Speculate on why this is the case. 

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. 

The requited characteristics of dyes used as passive mode-locking agents and as active laser media differ in essential ways. For passive mode-locking dyes, short excited-state relaxation times ate needed dyes of this kind ate characterized by low fluorescence quantum efficiencies caused by the highly probable nonradiant processes. On the other hand, the polymethines to be appHed as active laser media ate supposed to have much higher quantum efficiencies, approximating a value of one (91). 

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. 

Acantbephyra, 162, 336 Acantboscina, 336 Acholoe, 335 Achromobacter, 35, 36 Acorn worms (enteropneusts), 315 Acylhomoserine lactone, 43 Advice to students, 375 Aequorea, 159, 161, 162, 334, 375 Aequorea aequorea, 92-94, 346 collection, 93, 94 distribution, 92 squeezate, 94 synonyms, 92 Aequorea GFP, 150-154 chromophore, 153 cloning, 154 crystallization, 130 fluorescence quantum yield, 152 isolation, 129 molecular weight, 152 spectral properties, 130, 152 Aequorea victoria, 92 Aequorin, 92-129, 159, 160,172,173, 175, 346, 349, 350, 364, 375 assay, 98... 

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.

Table I. Effects of Peptide Substituents on Fluorescence Quantum...

Table II. A Comparisoa of Fluorescence Quantum Efficiencies (4>p) of OPA, Danysl, and CBI Derivatives in Aqueous-Organic Mixed Solvents...

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,... 

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