Phosphorescence characteristics

Lu, W., Li, Y, Chan, M.C.W., Che, C.-M., Cheung, K.-K and Zhu, N. (2002) Organic triplet emissions of arylacetylide moieties harnessed through coordination to [Au(PCy3)]. Effect of molecular structure upon photoluminescent properties. Journal of the American Chemical Society, 124,14696-14706 (c) Lu, W., Zhu, N. and Che, C.M. (2003) Polymorphic forms of a gold(I) arylacetylide complex with contrasting phosphorescent characteristics. Journal of the American Chemical Society, 125, 16081—16088 ... 

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). 

The phosphorescence characteristics of the copolymer yarns are somewhat unexpected. It has been shown previously that the terephthalate emission should predominate in the phosphorescence spectra. It has also been shown previously that in mixed... 

The aP4 white form is the most volatile, reactive (and highly toxic) and thermodynamically the least stable solid modification. The slow oxidation of the vapour over the solid results in the phosphorescence characteristic of this element. By heating above 180°C, white phosphorus is transformed into red phosphorus which... 

If the ligand triplet lies more than 2-3 kcal below the emitting level of the ions, energy is not transferred and broad molecular phosphorescence characteristic of the ligand is observed. Few other schemes are also visualized depending on the relative energy levels of ligand and the metal ions, such as ... 

Phenanthridine, like other monoazaaromatics which fluoresce only weakly in nonpolar solvents, is subject to marked fluorescence activation by hydroxylic solvents. Recent studies have shown this to result from the effects of solvent on vibronic interactions between re,77 and 77,77 electronic states, and the effect of solvent changes on the phosphorescence half-life has been similarly explained.237 Measurements of fluorescence and, more especially, phosphorescence characteristics have been proposed as analytical methods for mixtures containing phenanthridines238, 239 and detailed studies of the emission spectra of phenanthridine,240, 241 its cation,241 9-methylphenanthri-dine,242 and phenanthridine-iV-oxide243 have been reported. A... 

The photochemistry of polysilane derivatives may occur also via the triplet state 13, 30), on the basis of the observation of a weak-structured phosphorescence characteristic of a localized excited state for a number of polysilane derivatives. In principle, the halogenated additives could promote intersystem crossing via an intermolecular heavy-atom effect (39). Again, however, why the two structurally similar polysilanes should respond so differently to the presence of the additive is unclear. 

Kirkbright and co-workers [86] carried out a study of the general feasibility of the fluorimetric or phosphorimetric determination of stabiliser compounds after their extraction from polymers with organic solvents. They examined the fluorescence and phosphorescence characteristics of 29 common antioxidants and UV absorbers in an organic solvent medium at room temperature and -200 °C, respectively, and they report the fluorescence and phosphorescence spectral characteristics in a mixture of diethylether, isopentane, ethanol and chloroform and the calibration data phosphorescence detection limits and phosphorescence life-times. 

Ru(bpy)2 - chromophoric component) the following observations are made (i) the MLCT emission characteristic of the chromophoric unit is completely quenched (ii) the MC phosphorescence characteristic of the Cr(cyclam)(CN)2 luminophoric units is obtained with high efficiency. This demonstrates the occurrence of very efficient chromophore -> luminophore energy transfer. The behavior of the chromophore-luminophore complex is schematized on the energy level diagram of Fig. 16 [72]. 

Oxygen quenches phosphorescence of aromatic hydrocarbons in plastics at r.t. but not at liquid nitrogen temperature [547]. Luminescence spectroscopy (phosphorescence at 77 K and fluorescence at r.t.) may be used to evaluate oxidation processes in plastic materials, e.g. in LDPE films [548]. Recently, Allen et al. [549] have reported that prolonged melt oxidation of PET results in extensive discoloration and the formation of highly fluorescent hydroxy-lated terephthalate units which exist in equilibrium with highly phosphorescent stilbenequinone units. Phosphorescence characteristics of some common polymers are available [505]. 

The cocrystals of fluorene and its heterocyclic analogues, assembled using the new methodology, also emit strong phosphorescence. From the strucmre sections, it can be seen that 7 and 8 are very similar in structural features 9 and 10 also possess similar structures, although different fi om 7 and 8. An analogous trend was also observed in their phosphorescence behavior emission spectra of 7 and 8 are very similar 9 and 10 also show a similarity, which proves that phosphorescent properties can be modulated by the design of cocrystal structures. The phosphorescent characteristics are summarized in Table 6. 

Skrilec M, Love LJC (1981) Micelle-stabilized room-temperature phosphorescence characteristics of carbazole and related derivatives. J Phys Chem 85 2047-2050... 

The commonest form of phosphorus, and the one which is usually formed by condensation from the gaseous or liquid states, is the waxy, cubic, white form o -P4 (d 1.8232 gcm at 20°C). This, paradoxically, is also the most volatile and reactive solid form and thermodynamically the least stable. It is the slow phosphorescent oxidation of the vapour above these crystals that gives white phosphorus its most characteristic property. Indeed, the emission of yellow-green light from the oxidation of P4 is one of the earliest recorded examples of chemiluminescence, though the details of the reaction... 

After the laser flash, one then monitors the progress of events by some rapidly responding method. Conductivity, absorption spectroscopy, and fluorescence spectroscopy are the methods most commonly used. If a reaction product has a characteristic absorption band of sufficient intensity, one can monitor its buildup with time. This might be a UV, visible, or IR band. The need for a band with a high molar absorptivity arises because the reactive transient is usually present at a relatively low concentration, KT6-lCr5 M being typical. If the species of interest is phosphorescent, then the timed decay of its phosphorescence intensity can be recorded. 

The luminescence of an excited state generally decays spontaneously along one or more separate pathways light emission (fluorescence or phosphorescence) and non-radiative decay. The collective rate constant is designated k° (lifetime r°). The excited state may also react with another entity in the solution. Such a species is called a quencher, Q. Each quencher has a characteristic bimolecular rate constant kq. The scheme and rate law are... 

Cyclodextrins can solubilize hydrophobic molecules in aqueous media through complex formation (5-8). A nonpolar species prefers the protective environment of the CDx cavity to the hulk aqueous solvent. In addition, cyclodextrins create a degree of structural rigidity and molecular organization for the included species. As a result of these characteristics, these macrocycles are used in studies of fluorescence and phosphorescence enhancement (9-11), stereoselective catalysis (.12,13), and reverse-phase chromatographic separations of structurally similar molecules (14,15). These same complexing abilities make cyclodextrins useful in solvent extraction. 

The Characteristics of PLEDs Fabricated with Polymers Containing Phosphorescent Moieties as Pendant Groups (PFO Stands for PDOF 13)... 

The excitation spectrum of a molecule is similar to its absorption spectrum, while the fluorescence and phosphorescence emission occur at longer wavelengths than the absorbed light. The intensity of the emitted light allows quantitative measurement since, for dilute solutions, the emitted intensity is proportional to concentration. The excitation and emission spectra are characteristic of the molecule and allow qualitative measurements to be made. The inherent advantages of the techniques, particularly fluorescence, are ... 

Understand the principal mechanisms whereby certain molecules emit luminescence with the same spectral characteristics as fluorescence but with lifetimes more of the order of phosphorescence. 

In certain compounds a weak emission has been observed with the same spectral characteristics (wavelengths and relative intensities) as fluorescence, but with a lifetime more characteristic of phosphorescence. Two mechanisms are used to account for delayed fluorescence. 

The intensity of the delayed fluorescence emission from eosin decreases as the temperature is lowered and this indicates that an energy barrier is involved. Since the delayed fluorescence is spectrally identical to normal fluorescence, emission must occur from the lowest vibrational level of Si. However, the fact that the lifetime is characteristic of phosphorescence implies that the excitation originates from T,. The explanation of this requires a small Si-Ti energy gap, where T, is initially populated by intersystem crossing from Si. Ti to Si intersystem crossing then occurs by thermal activation. 

Attribution and characteristics PEN excimer fluorescence PEN monomer phosphorescence Emission peaking at 618nm, with a shoulder at 690 nm... 

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