Fluorescent materials

Purification of anthracene. Dissolve 0-3 g. of crude anthracene (usually yellowish in colour) in 160-200 ml. of hexane, and pass the solution through a column of activated alumina (1 5-2 X 8-10 cm.). Develop the chromatogram with 100 ml. of hexane. Examine the column in the hght of an ultra-violet lamp. A narrow, deep blue fluorescent zone (due to carbazole, m.p. 238°) will be seen near the top of the column. Immediately below this there is a yellow, non-fluorescent zone, due to naphthacene (m.p. 337°). The anthracene forms a broad, blue-violet fluorescent zone in the lower part of the column. Continue the development with hexane until fluorescent material commences to pass into the filtrate. Reject the first runnings which contain soluble impurities and yield a paraffin-hke substance upon evaporation. Now elute the column with hexane-benzene (1 1) until the yellow zone reaches the bottom region of the column. Upon concentration of the filtrate, pure anthracene, m.p. 215-216°, which is fluorescent in dayhght, is obtained. The experiment may be repeated several times in order to obtain a moderate quantity of material. 

Samples of urine that do not contain quinine still contain a small amount of fluorescent material after the extraction steps. Flow can the quantitative procedure described earlier be modified to take this into account ... 

Fluorescent Dyestuffs. Very few dyes are of use in making daylight-fluorescent products. Of the dyes discovered up to 1920, only the brilliant ted and salmon dyes of the rhodamine and rosamine classes ate used in fluorescent materials in the 1990s. The first of these, Rhodamine B, was discovered in 1877. Fluorescence excited by both uv and visible light components in daylight was formally recognized as a notable property of certain dyed fabrics by the 1920s (1). 

The total world marketplace can vary widely from year to year, however, due to the cyclic nature of the textile and coUateral appHcations which can be sizable but short-lived. Perhaps this is the reason that there are no published estimates for the world market for fluorescent color. Also, competition has forced most producers to develop higher strength fluorescent materials that offer greater color yield and a better money value. This reduces unit volume and, in many cases, doUar sales. 

Liquid scintillation counting is by far the most common method of detection and quantitation of -emission (12). This technique involves the conversion of the emitted P-radiation into light by a solution of a mixture of fluorescent materials or fluors, called the Hquid scintillation cocktail. The sensitive detection of this light is affected by a pair of matched photomultiplier tubes (see Photodetectors) in the dark chamber. This signal is amplified, measured, and recorded by the Hquid scintillation counter. Efficiencies of detection are typically 25—60% for tritium >90% for and P and... 

More objective laboratory methods employ a mechanical device such as a Terg-O-Tometer (110). Food soils are appHed to microscope sHdes or glass tape rather than to actual plates. The soils are tagged with fluorescent materials or with dark pigment to faciUtate measurement of residual soil. Reflectance or transmittance may also be read directly (111). 

Fluorescent materials are very important in medical research. Dyes such as fluorescein (21) can be attached to protein molecules, and the protein can be traced in a biological system by exciting the fluorescein and looking for its emissions. The use of a fluorescent material allows the detection of much smaller concentrations than would otherwise be possible. Because fluorescent materials can be activated by radioactivity, they are also used in scintillation counters to measure radiation (see Box 17.2). 

Self-Test 15.8A Explain how fluorescent materials can be used to detect radioactivity. 

Answer The fluorescent materials absorb energy from the radiation and release it as ight. ... 

These spherical nano-particles about 55 nm in diameter have a fluorescent material of ruthenium pyridine inside, and the shell of silicon dioxide, as shown in Fig. 36. The excitation wavelength of the ruthenium pyridine is 480 nm and the emission wavelength is 592 nm [81]. In order to get a clear image of nano-particles, the mass concentration of the fluorescent particles should be limited to a very low level. 

Tracer methods can also be used, in which tracers such as freon, fluorescent materials, and isotope-fuel are added to a tank, and are then detected externally. An analogy of tracer methods includes pressurizing the tank with a noble gas, then detecting the gas if it escapes from the tank through cracks or holes. 

The only lanthanide of which there is no stable isotope — they all decompose with half-lives between 2.6 and 17.7 years. Strong beta-emitters that are used industrially as thickness gauges. Also suitable as an additive for fluorescent materials. Produced artificially in kg amounts and serves as an energy provider for satellites in radionucleide batteries. Tiny batteries are long-term energy sources for pacemakers. 

The principal advantages of this technique are its very good time resolution, allowing the determination of lifetimes ranging from 10-e to 10-10 sec, and the fact that single photons are counted. Thus good results can be obtained even with very weakly fluorescent materials. 

This method is perfectly suitable for low concentrations of fluorescent materials. However, in order to study factors which affect the fluorescence quantum yield, such as molecular association or photochemical reactions, much higher concentrations than can be used in the right-angle fluorescence method are required. This follows from the fact that the 0 - 0 vibrational bands in the absorption and emission spectra often overlap. Therefore at relatively high concentrations light emitted at these overlapping wavelengths will be reabsorbed. 

Fluorescence Analysis of Irradiated PET and PET-co-4,4 -BPDC Yarns. The presence of a material, which emits a blue-green fluorescence, on photooxidized PET has been reported previously (2, 21). This fluorescent material, which emits at 460 nm when excited by 342 nm energy, has been proved to be monohydroxy-tere-phthalate. 

In spite of the great demand for fluorescent materials, the availability of novel molecular frameworks - critical components of new fluorescent probes - is quite limited. Recently, our research group reported the development of full-color-tun-able fluorophores based on the novel core skeleton, 1,2-dihydropyrrolo 3,4-(i indolizin-3-one, using a combinatorial approach [92], We developed a new... 

Figure 29 (Qin and Liu, 1982) shows the behavior of individual particles above the distributor recorded by video camera of small clusters of particles, coated with a fluorescent material and spot-illuminated by a pulse of ultra violet light from an optical fiber. The sequential images, of which Fig. 29 just represents exposures after stated time intervals, were reconstructed to form the track of motion of the particle cluster shown in Fig. 30. Neither this track nor visual observation of the shallow bed while fluidized, reveal any vestige of bubbles. Instead, the particles are thrown up by the high velocity jets issuing from the distributor orifices to several times their static bed height.

Under this heading are discussed both the naturally occurring fluorescent material and the yellow substances which give coastal waters their generally greenish colour. It is usually considered that these two categories are the same, or at least overlap almost entirely. 

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