Phosphorescent compounds, chemical

Fig. 3 Chemical structures of some fluorescent and phosphorescent compounds.

Interactions in Solid-Surface Luminescence Temperature Variation. Solid-surface luminescence analysis, especially solid-surface RTF, is being used more extensively in organic trace analysis than in the past because of its simplicity, selectivity, and sensitivity (,1,2). However, the interactions needed for strong luminescence signals are not well understood. In order to understand some of the interactions in solid-surface luminescence we recently developed a method for the determination of room-temperature fluorescence and phosphorescence quantum yields for compounds adsorbed on solid surfaces (27). In addition, we have been investigating the RTF and RTF properties of the anion of p-aminobenzoic acid adsorbed on sodium acetate as a model system. Sodium acetate and the anion of p-aminobenzoic acid have essentially no luminescence impurities. Also, the overall system is somewhat easier to study than compounds adsorbed on other surfaces, such as filter paper, because sodium acetate is more simple chemically. 

In 1962, Parker and Hatchard described a photoelectric spectrometer for phosphorescence measurements with which they were capable of obtaining phosphorescence spectra, and of determining lifetimes and quantum efficiencies of a large number of organic compounds. This work stimulated intensely the interest in the phosphorimetry of diverse chemical analytes [5], and one year later, Wine-... 

Figure 10.5 Quenching by oxygen affects the phosphorescence emission arising from Dj but has no effect on the photosolvation reaction that occurs from Q, Adapted from F. Scandola and V. Balzani, Energy-Transfer Processes of Excited States of Coordination Compounds , Journal of Chemical Education, Volume 60 (10), 1983. American Chemical Society...

The basis for the claim of discovery of an element has varied over the centuries. The method of discovery of the chemical elements in the late eightenth and the early nineteenth centuries used the properties of the new sustances, their separability, the colors of their compounds, the shapes of their crystals and their reactivity to determine the existence of new elements. In those early days, atomic weight values were not available, and there was no spectral analysis that would later be supplied by arc, spark, absorption, phosphorescent or x-ray spectra. Also in those days, there were many claims, e.g., the discovery of certain rare earth elements of the lanthanide series, which involved the discovery of a mineral ore, from which an element was later extracted. The honor of discovery has often been accorded not to the person who first isolated the element but to the person who discovered the original mineral itself, even when the ore was impure and that ore actually contained many elements. The reason for this is that in the case of these rare earth elements, the earth now refers to oxides of a metal not to the metal itself This fact was not realized at the time of their discovery, until the English chemist Humphry Davy showed that earths were compounds of oxygen and metals in 1808. 

The only materials that have been examined for this purpose to date have been dienes and other polyenes.12 The major liability of these substances is their chemical reactivity. The finding that 1,3,5-trans-hexatriene quenches the phosphorescent emission from phenanthrene but does not have a significant effect on the fluorescent emission from 1,3,5,7-tetraphenylisobenzofuran indicates that chemical reactivity may not be too severe a problem, and that triplet quenchers may be effective tools for mechanistic work in ECL. Here too, further study is indicated. Unfortunately, or perhaps significantly, the compounds that produce the brightest emission on redox stimulation—1,3,4,7-tetra-phenylisobenzofuran and rubrene—have no detectable phosphorescence. Studies with sensitizers and quenchers have failed to produce any evidence regarding their triplet levels.12 Thus the mechanism of anni-hilative emission remains uncertain. 

Triplet decay processes most interesting to photochemists involve molecular rearrangements and reactions with other compounds. It must be emphasized that the rates of these chemical reactions vary over many orders of magnitude so that some occur to the exclusion of physical decay while others barely compete with phosphorescence,... 

Barnett NW, Hindson BJ, Jones P, Smith TA. Chemically induced phosphorescence from manganese(II) during the oxidation of various compounds by manganese(III), (IV) and (VII) in acidic aqueous solutions. Anal Chim Acta 2002 451 181-8. 

Triplet state data for azobenzene-type azo compounds are very limited. Direct absorption of a 0.51 mol solution in C7H15J in 5 cm cells has not been detectable. Neither has phosphorescence been detected. The energy of triplet states has been located only by chemical spectroscopy, i.e., the quenching of other molecules triplet states by azobenzene. Ronayette et found two relevant triplet states at about 196 and 180 kj moH... 

The reaction-rate constant kjfP is a chemical constant characteristic of a compound P with general validity. It can be measured in laboratory experiments designed to isolate the effect of a single environmental factor j. Often, for practical reasons, it is determined only relative to that of a well-studied model compound with an absolute rate constant known for the same reaction. In case of slow reactions it is generally easy to measure absolute rate constants directly. For the study of fast reactions, sophisticated short-time measurements, such as pulse radiolysis or flash photolysis, typically combined with kinetic absorption spectroscopy or kinetic phosphorescent measurements, must be applied. 

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