Naphthalene fluorescence efficiency

The same authors studied the CL of 4,4,-[oxalylbis(trifluoromethylsulfo-nyl)imino]to[4-methylmorphilinium trifluoromethane sulfonate] (METQ) with hydrogen peroxide and a fluorophor in the presence of a, p, y, and heptakis 2,6-di-O-methyl P-cyclodextrin [66], The fluorophors studied were rhodamine B (RH B), 8-aniline-l-naphthalene sulfonic acid (ANS), potassium 2-p-toluidinylnaph-thalene-6-sulfonate (TNS), and fluorescein. It was found that TNS, ANS, and fluorescein show CL intensity enhancement in all cyclodextrins, while the CL of rhodamine B is enhanced in a- and y-cyclodextrin and reduced in P-cyclodextrin medium. The enhancement factors were found in the range of 1.4 for rhodamine B in a-cyclodextrin and 300 for TNS in heptakis 2,6-di-O-methyl P-cyclodextrin. The authors conclude that this enhancement could be attributed to increases in reaction rate, excitation efficiency, and fluorescence efficiency of the emitting species. Inclusion of a reaction intermediate and fluorophore in the cyclodextrin cavity is proposed as one possible mechanism for the observed enhancement. 

Substituent groups have a marked effect on the fluorescence quantum yield of many compounds. Electron-donating groups such as -OH, -NH2 and -NR.2 enhance the fluorescence efficiency, whereas electron-withdrawing groups such as -CHO, -C02H and -N02 reduce the fluorescence quantum yield, as shown by naphthalene and its derivatives in Table 4.3. 

Table 4.3 The effect of substituent groups on fluorescence efficiency of naphthalene and its derivatives. Fluorescence quantum yields measured in fluid solution at room temperature...

The aqueous cores of reverse micelles are of particular interest because of their analogy with the water pockets in bioaggregates and the active sites of enzymes. Moreover, enzymes solubilized in reverse micelles can exhibit an enhanced catalytic efficiency. Figure B4.3.1 shows a reverse micelle of bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane with three naphthalenic fluorescent probes whose excited-state pK values are much lower than the ground-state pK (see Table 4.4) 2-naphthol (NOH), sodium 2-naphthol sulfonate (NSOH), potassium 2-naphthol-6,8-disulfonate (NSOH). The spectra and the rate constants for deprotonation and back-recombination (determined by time-resolved experiments) provide information on the location of the probes and the corresponding ability of their microenvironment to accept a proton , (i) NDSOH is located around the center of the water pool, and at water contents w = [H20]/[A0T] >... 

If one of the substances has a known fluorescence efficiency, the value of the other is then simply obtained. Convenient standard solutions are rhodamine B in ethanol with fluorescence in the yellow and efficiency 0.69, quinine bisulfate in 0.1 N sulfuric acid with fluorescence in the blue and efficiency 0.55. anthracene in ethanol with fluorescence in the violet and efficiency 0.27 in the ultraviolet region, naphthalene ( = 0.19), phenol (0 = 0.19), or benzene (0 = 0.042) can be used. With the last four compounds the solution must be deaerated by passing a current of nitrogen before measurement. To minimize the effect of errors in the spectral sensitivity curve it is desirable to use as the standard a solution... 

The inteipolymer cholesterol association is indicated by NRET between a naphthalene-labeled polymer [poly(A/Chol-C5-MA5/Np)] and a pyrene-labeled polymer [poly(A/Chol-C5-MA5/Py)J (Chart 1). In Figure 2, the intensity ratios of pyrene fluorescence to naphthalene fluorescence (Ipy/Iup) in fluorescence spectra of mixtures of the pyrene-labeled and naphthaiene-labeied polymers in water are plotted as a function of the total polymer concentration. The /py//Np ratio is a measure for the quantum efficiency of NRET between the naphthalene and pyrene labels. Naphthalene can be predominantly excited at 290 nm with a slight contribution of direct excitation of pyrene, which can be corrected for the estimation of /py/Zwp (44-46), In a concentration range from 0.02 to 0.9 g/L, the /py//Np ratio appears to increase slightly as the pol) er concentration is increased, but the ratio increases more significantly in a concentration regime > 1 g/L. This increase in /py//Np is due to a decrease in the... 

Nevertheless the fluorescence efficiency of the substituted phthalate dianion is a decisive factor in luminol type chemiluminescence. Since one can expect that the carboxylates of higher condensed aromatic hydrocarbons would exhibit high fluorescence efficiencies, a series of naphthalene-, anthracene- and homologuous o-dicarboxylic acid hydrazides have been synthesized and their chemiluminescence investigated. In the tables in Appendix, p. 205 some of these hydrazides synthesized since 1968 are listed. 

Changes in pH affect several properties. One of the most important is the fluorescence efficiency of the product dicarboxylate. The most thoroughly investigated compound 3-aminophthalate (p. 82) has its maximum fluorescence yield at pH 11-11.4 (cf. p. 84). Dialkylamino-substituted phthalic or naphthalene dicarboxylic acid dianions reach their maximum fluorescence yield at a somewhat higher pH [8]. 

Finally, we have also attempted to improve on the fluorescence and chemiluminescence efficiencies of the labeling reagent, the naphthalene dialdehyde. Derivatives 7, 8, and 9 (Table IX) have been synthesized and studied. As shown in Table IX, none of these new derivatives presents an advantage over the parent unsubstituted CBI-Ala. 

They observed a constant quantum yield of fluorescence (Or = 0.3) for all members of the series independent of whether the anthracene moiety absorbed and emitted the energy or the naphthalene moiety absorbed the energy and transferred it to the anthracene moiety. Thus at these short distances singlet energy transfer is 100% efficient. 

Steel and coworkers194 have also noted that 2,3-diazabicyclo[2.2.1]-heptene-2 (39) quenches the fluorescence of naphthalene. A more extensive study of this compound was carried out by Engel195 who reported that there was a sharp drop in the efficiency of sensitized decomposition and in the rate of sensitizer fluorescence quenching as the sensitizer singlet energy fell below that of 39. This points out a key difference between azo compounds and the cases discussed previously namely, there is a spectroscopic azo singlet state lying below that of the sensitizer. 

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