Rhodamine fluorescence efficiency

A wide variety of different classes of fluorescent molecules has been investigated in the peroxyoxalate chemiluminescent systems. Among those screened were fluorescent dyes such as rhodamines and fluoresceins, heterocyclic compounds such as benzoxazoles and benzothiazoles, and a number of polycyclic aromatic hydrocarbons such as anthracenes, tetracenes, and perylenes. The polycyclic aromatic hydrocarbons and some of their amino derivatives appear to be the best acceptors as they combine high fluorescence efficiency with high excitation efficiency in the chemiluminescent reaction [28],... 

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. 

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... 

As already mentioned in Sect. 4.1, the fluorescence behavior of many dye systems can be rationalized using the TICT model. For example, the fluorescence efficiency of xanthene dyes and derivatives like rhodamine and oxazine dyes correlates with the donor strength of the amino groups as predicted from... 

The fraction of excited molecules which fluoresce is known as the quantum efficiency and approaches 100% for compounds such as rhodamine B or fluorescein. The higher the quantum efficiency, the greater the fluorescence of the compound. The intensity of the fluorescence, F, is also dependent on the energy of the incident light and the concentration of the fluorescent species ... 

Function of mitochondria is also commonly monitored as an indicator of cellular toxicity. Mitochondrial uptake and retention of the fluorescent dye, rhodamine 123, can be visualized microscopically. Biochemical measurements of mitochondrial function include the ATP-ADP ratio and dehydrogenase activity with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), which yields a colored formazan product upon reduction. The dye, neutral red (3-amino-7-dimethyl-amino-2-methylphenazine hydrochloride), targets lysosomes, and its retention is inversely related to cytotoxicity. Commercially available versions of the MTT and neutral red assays have been adapted to microtiter plate formats to provide highly efficient screening assays. Examples of how cell-type-specific functions can be followed as indicators of cell toxicity are included in Table 8.1. 

Some lanthanide ions when complexed with UV-absorbing ligands, can efficiently accept energy from the excited state of the ligand and produce highly enhanced emission characteristics of the metal ion. Rare earth complexes have some advantages over organic fluorescent probes such as fluorescein, rhodamines, umbelliferones such as... 

The model of ionic binding was also evaluated by comparing the binding of fluorescein and rhodamine to hair, two molecules of similar shape, size, and fluorescent quantum yield. Rhodamine, being positively charged, is far more efficient at binding to hair compared to fluorescein. The disparity in binding of materials to... 

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