Phosphorescence aromatic compounds

Stabilisers are usually determined by a time-consuming extraction from the polymer, followed by an IR or UV spectrophotometric measurement on the extract. Most stabilisers are complex aromatic compounds which exhibit intense UV absorption and therefore should show luminescence in many cases. The fluorescence emission spectra of Irgafos 168 and its phosphate degradation product, recorded in hexane at an excitation wavelength of 270 nm, are not spectrally distinct. However, the fluorescence quantum yield of the phosphate greatly exceeds that of the phosphite and this difference may enable quantitation of the phosphate concentration [150]. The application of emission spectroscopy to additive analysis was illustrated for Nonox Cl (/V./V -di-/i-naphthyl-p-phcnylene-diamine) [149] with fluorescence ex/em peaks at 392/490 nm and phosphorescence ex/em at 382/516 nm. Parker and Barnes [151] have reported the use of fluorescence for the determination of V-phenyl-l-naphthylamine and N-phenyl-2-naphthylamine in extracted vulcanised rubber. While pine tar and other additives in the rubber seriously interfered with the absorption spectrophotometric method this was not the case with the fluoromet-ric method. 

Ellis DW (1979) Analysis of aromatic compounds in water using fluoresence and phosphorescence. PB report no. 212268. National Technical Information Service, Springfield, VA, USA... 

Substituents have considerable influence on emission characteristics of aromatic compounds. Heavy atom substituents tend to reduce the fluorescence quantum yield 4>f in favour of phosphorescence emission f. In halogen series the effect increases in the order F < Cl < Br < I. In Table 5.1 are recorded experimental data for halogen substituted Naphthalenes. 

Experimental Zero-Field Splittings of Some Nitrogen-Containing Aromatic Compounds in Their Phosphorescent Triplet State3... 

A review of chemiluminescent and bioluminescent methods in analytical chemistry has been given by Kricka and Thorpe. A two-phase flow cell for chemiluminescence and bioluminescencc has been designed by Mullin and Seitz. The chemiluminescence mechanisms of cyclic hydrazides, such as luminol, have been extensively analysed. " Fluorescence quantum yields of some phenyl and phenylethynyl aromatic compounds in peroxylate systems have been determined in benzene. Excited triplet states from dismutation of geminate alkoxyl radical pairs are involved in chemiluminescence from hyponitrite esters. Ruorophor-labelled compounds can be determined by a method based on peroxyoxalate-induced chemiluminescence. Fluorescence and phosphorescence spectra of firefly have been used to identify the multiplicity of the emitting species. " The chemiluminescence and e.s.r. of plasma-irradiated saccharides and the relationship between lyoluminescence and radical reaction rate constants have also been investigated. Electroluminescence from poly(vinylcarbazole) films has been reported in a series of four... 

Room-temperature phosphorescence (RTF) techniques in which the sample is adsorbed onto an inert solid support are proving valuable in the analysis of traces of polynuclear aromatic compounds (Parker et al. Vo-dinh et al.). Useful techniques are being developed for the hitherto troublesome resolution of n-component fluorescence decays (Weber and Jameson Slifkin and Darby). 

For a complete picture, we should briefly refer to the influence of the chemical structure of the emitting molecule. As with fluorescence, aromatic compounds are most important because they may yield phosphorescence. A shift of this emission toward longer wavelengths with an increase in the number of condensed benzene rings is observed. Introduction of a heteroatom into the aromatic electron system (e.g., in a polyaromatic hydrocarbon) or substitution by atoms of high atomic number (e.g., the internal heavy-atom effect of bromine or iodine) usually... 

Nevertheless, analytical problems can be found where such disadvantages can be outweighed by the convenient final resolution of the problem based on LTP data. On other occasions, both fluorescence and phosphorescence data can easily be obtained from a given sample, providing complementary information. One example is the use of phosphorescence measurements at low temperature to examine mixtures of aromatic compounds dissolved in -alkanes (Shpol skii spectrometry). The narrow-band fluorescence and phosphorescence spectra complement one another and have proved most useful in the analysis of complex samples such as multicomponent mixtures of polycyclic aromatic hydrocarbons (PAHs) in fuel materials. 

In a typical experiment for CD-RTP analysis of PAHs an aliquot of the compovmd of interest is added to a flask and the solvent is evaporated gently on a hot plate. An aliquot of 1,2-dibromomethane or 2-bromoethanol (heavy-atom species) is then added, followed by an aliquot of 0.1 mol 1 sodium sulfite (oxygen scavenger), and final dilution with 0.01 mol 1 aqueous CD solution. The solution is shaken vigorously by hand. Some precipitation, usually due to inclusion of excess heavy atom by CD, may cause cloudiness in the solution, which does not affect the reproducibility and quality of phosphorescence spectra. Sample preparation time is less than 5 min in this method. Cline Love and colleagues reported RTP detection limits for several polynuclear aromatic compounds (naphthalene, biphenyl, phenanthrene, etc.) in CD solution in the range 10 -10 moll . ... 

Bronislaw Znatowicz (1851-1917), chemist, professor at Warsaw University, co-founder and first editor-in-chief of the journal Chemik Polski, author and translator of chemical textbooks and monographs. He investigated the reduction and nitration of aromatic compounds and the production of dyes from tar, and studied the phenomenon of phosphorescence and electrolysis of organic compounds. 

Emission of UV/VIS radiation Molecular fluorescence, molecular phosphorescence Detection of small quantities (aromatic compounds and natural products, analysis of gels and glasses, determination of organic and inorganic species by tagging ... 

It is well established that o grgen quenches both excited singlet and triplet states of aromatic compounds. Thus, indole derivatives in solution at room temperature display a ratio for the rate constant Icnk/I qp of approximately two (48, 49). However, the quenching of alkaline phosphatase phosphorescence by oxygen proceeds at a rate kqp = 1.2 x lO s (47). The magnitude of this rate... 

Phosphorescence is also enhanced when luminophores are included in the cyclodextrin cavity. This room temperature phosphorescence (RTP) proved itself to be a useful analytical technique. In conventional liquid media, polycyclic aromatic hydrocarbons (PAHs) do not show any appreciable phosphorescence, especially at room temperature. However, when a stable ternary complex is formed with the aromatic compound, /S-cyclodextrin, and an intersystem crossing promoter such as 1,2-dibromoethane, intense phosphorescence is observed. ... 

Electron transfer rates between adrenaline and related benzene diols and complexes of iron(III) with some substituted 1,10-phenanthrolines have been reported [67] in surfactant systems. In cationic systems the reactions take place in the aqueous phase and reaction rates are lower than they are in simple aqueous systems, but in anionic surfactant systems the reaction rates are enhanced, reactions probably taking place at the micellar interface. The rates of exit and entrance of aromatic compounds from and into micelles have recently been studied using phosphorescence decay measurements [68] exit rate constants of aromatic hydrocarbons are of the order of 10 to 10 s " S whereas values of 10 to 10 (moll ) s have been reported for intramicellar energy transfer processes. Release of aromatic phosphorescence probes from micelles followed by their deactivation in the aqueous phase is hence expected to be an important mode of deactivation of the triplet state [69]. Kinetic schemes for triplets that are partitioned between aqueous and micellar phases are considered for the cases of single occupancy and double occupancy of the micellar units. 

Organic Analytes As noted earlier, organic compounds containing aromatic rings generally are fluorescent, but aromatic heterocycles are often phosphorescent. Many important biochemical, pharmaceutical, and environmental compounds are aromatic and, therefore, can be analyzed quantitatively by fluorometry... 

Thus we see that in molecules possessing ->- 77 excited states inter-combinational transitions (intersystem crossing, phosphorescence, and non-radiative triplet decay) should be efficient compared to the same processes in aromatic hydrocarbons. This conclusion is consistent with the high phosphorescence efficiencies and low fluorescence efficiencies exhibited by most carbonyl and heterocyclic compounds. 

Of particular interest in the application of cyclodextrins is the enhancement of luminescence from molecules when they are present in a cyclodextrin cavity. Polynuclear aromatic hydrocarbons show virtually no phosphorescence in solution. If, however, these compounds in solution are encapsulated with 1,2-dibromoethane (enhances intersystem crossing by increasing spin-orbit coupling external heavy atom effect) in the cavities of P-cyclodextrin and nitrogen gas passed, intense phosphorescence emission occurs at room temperature. Cyclodextrins form complexes with guest molecules, which fit into the cavity so that the microenvironment around the guest molecule is different from that in... 

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