Phosphorescence measurements

In principle, measurement of the phosphorescence characteristics of samples obtained after extraction of polymers with organic solvents may also yield useful information regarding the nature and concentration of the additives present. Parker and Hatchard [157] have examined the possibilities of phosphorescence measurements for V-phenyl-2-naphthylamine. Although it should be possible to determine various analytes simultaneously by correct choice of ex and em wavelengths and phosphorescence decay, no pertinent reports are available. Phosphorescence finds limited application for the direct determination of additives in polymers (without prior extraction). 

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-... 

The uses of micelles in chemical analysis are rapidly increasing (Hinze, 1979). Analytical reactions are carried out typically on a small scale and are based on spectrophotometry. At the same time, undesired side reactions can cause major problems, especially when the analytical procedure depends on reactions which are relatively slow and require high temperatures, exotic solvents or high reagent concentrations for completion. Micelles can suppress undesired reactions as well as speed desired ones and they also solubilize reagents which are sparingly soluble in water. In addition it is often possible to make phosphorescence measurements at room temperature in the presence of surfactants which enormously increases the utility of this very sensitive method of detection. 

Studies on the dynamics of complexation for guests with cyclodextrins have been carried out using ultrasonic relaxation,40 151 168 temperature jump experiments,57 169 183 stopped-flow,170,178,184 197 flash photolysis,57 198 202 NMR,203 205 fluorescence correlation spectroscopy,65 phosphorescence measurements,56,206 and fluorescence methods.45,207 In contrast to the studies with DNA described above, there are only a few examples in which different techniques were employed to study the binding dynamics of the same guest with CDs. This probably reflects that the choice of technique was based on the properties of the guests. The examples below are grouped either by a type of guest or under the description of a technique. 

The pulsed xenon lamp forms the basis for both fluorescence and phosphorescence measurement. The lamp has a pulse duration at half peak height of lOps. Fluorescence is measured at the instant of the flash. Phosphorescence is measured by delaying the time of measurement until the pulse has decayed to zero. 

Fluorescence and phosphorescence measurements. Steady-state fluorescence... 

Phosphorescence measurements of eosin in ethanol place the 0-0 transition of 3Si 3S0 at 7150 A.98 Recent determinations of phosphorescence spectra of xanthene dyes in EPA at 77°K show these transitions to occur in the region of 7000 A 94,103 (Table I). The triplet energies of these dyes, 3Bi, are thus about 40 kcal/mole and the energy separations between the excited singlet and triplet states, AE = Elai — 3si, are about 12-13 kcal/mole. 

The singlet energy of 2//-pyrans 467a and the singlet-triplet energy gap were estimated to be 368 kJ/mol and 105-125 kJ /mol on the basis of fluorescence and phosphorescence measurements.392,454a... 

Remarkably, one study [19] reported that ODPM rearrangement is also possible from the singlet excited state, but this is a matter of debate. For the triplet excited state of these (3,y-unsaturated ketones, it was clearly pointed out that it is nn in origin based on low temperature phosphorescence measurements, theoretical and mechanistic studies [20-23]. Furtheron, these phosphorescene and mechanistic studies indicated that the 37i7i excited state is approx. 8-12kcal/mol lower to the corresponding 3nn excited state [25]. 

Phosphorescence measurements of benzophenone adsorbed on Ti/Al binary oxides show the presence of its protonated form in addition to benzophenone hydrogen-bonded to surface OH groups (Nishiguchi... 

In Scheme 10 electron transfer to singlet state is portrayed. The plots obtained are also consistent for a process which involves electron transfer to the triplet state. However, using the values of the (slope)/(intercept) for plots of l/4> vs. 1/[A] for 17,18 and 19 in the exciplex dominant region and the values of the triplet lifetimes obtained from phosphorescence measurements (112, 36, and 29 ms), values of kex 10 - 102M 1s 1 are obtained which are too low. Estimating the inherent radiative lifetime from the molar absorptivity, kisc must be 109 - 1010 s 1, since no detectable fluorescence was observed. The slope over the intercept using Eq. 16 now yields values 109 — 1010 M "1 s 1 for kex which is more reasonable [39]. 

Nord K, Karlsen J, Tormesen HH. Photochemical stability of biologically active compounds. IX. Gharacterization of the spectroscopic properties of the 4-aminoquinolines chloroquine, hydroxychloroquine and selected metabolites by absorption, fluorescence and phosphorescence measurements. Photochem Photobiol 1994 60 427-431. 

Intersystem crossing efficiencies have been measured for [Cr(en)3] and are constant over the range 457.9—514.5 nm. This result is obtained from phosphorescence measurements and is in agreement with conclusions reached... 

Determined by phosphorescence measurements in glassy solution at 77 K., as a function of ntqthdialene concentration used as a quencher... 

Taking into account that for poIy(VBP-co-DMAS) a pronounced tendency to exciplex formation is observed by phosphorescence measurements [54-57], the above results can be interpreted [20,22] by assuming the occurrence of cage selfcombination of the amine-derived radicals (formed by hydrogen transfer within the radical ion pairs) due to their high local concentration along the polymer... 

Because of the long radiative lifetime of the lowest triplet state, most phosphorescence in fluid solutions is obviated by collisional quenching, especially by dissolved molecular oxygen. Phosphorescence, when it occurs, is usually observed at low temperatures (e.g., that of liquid nitrogen) in rigid matrices where it may demonstrate high quantum yields. In the past three decades, much interest has been focused on phosphorescence at room temperature (RTP), which sometimes can be observed in samples adsorbed on solid substrates such as filter paper. Unfortunately, the quantum yields observed in room temperature phosphorescence are low, leading to poor analytical sensitivity, and the method has not enjoyed wide popularity. Phosphorescent measurements at low temperatures... 

Because of its weak intensity, phosphorescence is much less widely applicable than fluorescence. However, phosphorimetry has been used for the determination of a variety of organic and biochemical species including nucleic acids, amino acids, pyrine and pyrimidine, enzymes, polycyclic hydrocarbons, and pesticides. Many pharmaceutical compounds exhibit measurable phosphorescence signals. The instrumentation for phosphorescence is also somewhat more complex than that for fluorescence. Usually, the phosphorescence instrument allows discrimination of phosphorescence from fluorescence by delaying the phosphorescence measurement until the fluorescence has decayed to nearly zero. Many fluorescence instruments have attachments, called phosphoroscopes, that allow the same instrument to be used for phosphorescence measurements. 

An important implication from Eq. 2 is that the observed phosphorescence spectra are (always) already relaxed within the time resolution of the measurement of phosphorescence spectra. Therefore, the true triplet energy (center of the triplet DOS) is always higher than the apparent phosphorescence spectra, which sets a lower limit only. For PF2/6 the true triplet level is calculated to be 2.26 eV instead of the observed 2.15 eV [24] from phosphorescence measurement. This higher value however agrees very well with that measured using the pulse radiolysis energy transfer technique which yields triplet energies in the initial unrelaxed state [71]. 

Instrumentation. Steady state luminescence measurements were made using a Perkin-Elmer MPF-3L spectrofluorimeter. Samples were contained in an optical dewar and temperature variation achieved using a flow of pre—heated or cooled dry nitrogen gas. Phosphorescence measurements were made using a rotating-can phosphoroscope. 

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. 

For most proteins, intrinsic triplet lifetimes of aromatics are quite short at room temperatures and thus triplet dye labels must be used. Our own experience has been with the use of triplet probes and triplet anisotropy decay. Since this is somewhat of a new, and we believe under-utilized, field, we will stress it here. Because the triplet yield is usually quite small and either low sensitivity absorption techniques or very low quantum yield phosphorescence measurements must be made, a reasonably high-powered laser is necessary for this kind of experiment. 

Note nd means not determined DF is 2,5-dimethylfuran. a Phosphorescence measured in an ethanol glass at 77 K (drug in neutral form). 

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