Phosphorescence reduced system

Because the relaxation rates of zero-field sub-levels were found to be much reduced by lowering the temperature from 4.2 K, the spin sub-levels in many molecules could be isolated from each other at 1.25 K. During the decay of such an isolated triplet spin system, drastic changes could be induced in the phosphorescence intensity by the sudden irradiation of a microwave transition between a pair of levels. Through such microwave-induced delayed... 

Radical 80 has been prepared as its perchlorate salt by anodic oxidation in ethyl acetate in the presence of hthium perchlorate. The reactivity toward nucleophiles of material so prepared was investigated nitrite and nitrate ions give 2-nitrodibenzo[l,4]dioxin although the mechanisms of the reactions are not clear. Pyridine gives 7V-(2-dibenzo[l,4]dioxinyl)pyridinium ion (84). Other nucleophiles acted as electron donors and largely reduced 80 back to the parent heterocycle they included amines, cyanide ion and water. In an earlier study, the reaction of 80 with water had been examined and the ultimate formation of catechol via dibenzo[l,4]dioxin-2,3-dione was inferred. The cation-radical (80) has been found to accelerate the anisylation of thianthrene cation-radical (Section lII,C,4,b) it has been found to participate in an electrochemiluminescence system with benzo-phenone involving phosphorescence of the latter in a fluid system, and it has been used in a study of relative diffusion coefficients of aromatic cations which shows that it is justified to equate voltammetric potentials for these species with formal thermodynamic redox potentials. The dibenzo[l,4]dioxin semiquinone 85 has been found to result from the alkaline autoxidation of catechol the same species may well be in-... 

Figure 27-5 The optical system for measurement of PO The optica system for PO2 is based on the ability of O2 to reduce the intensity and lifetime of phosphorescence from a phosphorescent dye that is in contact with the sample. The optica system comprises a green (519-nm peak) light-emitting diode (LED, that emits light, which is reflected by a dichroic mirror onto the PO2 sensor. Because of the phosphorescence, red light (672-nm peak) is emitted back through the dichroic mirror and onto a photodetector. (From Boaith N,Wandrup J, Larsson L, et al. Blood gases and oximetry calibration-free new dry chemistry and optical technology for near-patient testing. Clin Chim Acta 2001 307 225-33.)...

Exciplex Emission A solution to obtain white light while reducing the number of layers and dopants is to use a broadly emitting exciplex (i.e., an excited state formed by two charges located on two dissimilar molecules). Fluorescent exciplex systems exhibit low efficiency [252], but phosphorescent ones lead to broad efficient WOLED [253]. 

Silver also has been demonstrated to be reactive in solution systems. Thus, silver perchlorate has been shown to influence the photochemical reactivity of stilbene in acetonitrile and methanol. The fluorescence of the stilbene is quenched on addition of the perchlorate and this is good evidence for the enhancement of the So-Ti crossing induced by the heavy ion Ag+. It seems likely that an Ag+/stilbene complex is formed. The perturbation of the system is better in methanol than in acetonitrile. However, cis.trans isomerism of the stilbene is reduced within the excited Ag+/stilbene complex since it is difficult for the geometrical isomerism to occur. Enhanced isomerism is observed with the Ag+/azobenzene system. In this complex there are steiic problems encountered in the nitrogen rehybridization process that is operative in the isomerism . Enhanced So-T crossing is also seen in the Ag+/1 1 complex with tryptophan where the fluorescence is quenched and there is a threefold increase in phosphorescence . Complexes between Ag+ and polynucleotides and DNA cause quenching of the fluorescence. Enhancement of phosphorescence and a 20-fold increase in the dimerization of thymine moieties has also been observed when silver ions are added to the reaction system . ... 

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