Pyrene solution

The reactivity of pyrene anion radical toward ArS02R may be demonstrated as follows adding some ArS02R to the pyrene solution leads to an increase of the peak current corresponding to reduction of the pyrene, while this step becomes progressively irreversible. It may also be noted that for small amounts of ArS02R, the specific step for the sulphone more or less vanishes. This corresponds to the following scheme ... 

Fig. 11. Luminescence of impurities in ethanol at 20°C. sensitized by 10 Mf phenanthrene. Rate of light absorption was 0.7 X 10- einstein liter-1 sec.-1 at 341 to 362 mji. (a) normal fluorescence (b) and (c) delayed fluorescence at 1000 times greater sensitivity (d) fluorescence of dilute pyrene solution. Photodecomposition of (i>) to give (c) was produced by irradiation for 30 min. with rate of light absorption equal to 10 - einstein liter-1 sec.-1.

The normal violet fluorescence band of pyrene solutions shows concentration-quenching which is accompanied by the appearance of a blue structureless emission band. Forster and Kasper40 showed that the blue band is due to emission from an excited dimer formed by the combination of an excited singlet molecule with a molecule in the ground state. Most of the light in both spectral bands has a relatively short lifetime but Stevens and Hutton87 observed a long-lived component of the dimer... 

In some cases, simultaneously with the quenching of the normal fluorescence a new structureless emission band appeals at about 6000 cm-1 to the red side of the monomer fluorescence spectrum (Figure 6.4). This phenomenon was first observed in pyrene solution by Forster and was explained as due to transitory complex formation between the ground and the excited state molecules since the absorption spectrum was not modified by increase in concentration. Furthermore, cryoscopic experiments gave negative results for the presence of ground state dimers. These shortlived excited state dimers are called pxcimers to differentiate them from... 

In higher concentration ranges some aromatic hydrocarbons form dimers. Several distinct types of reaction have been found. Pyrene solutions fluoresce violet when dilute and blue when stronger, and the behavior has been attributed to process 5 followed by 9 (29). 

The resulting local and bulk densities for pyrene in CO2 at Tr=1.02 are given in Table I. Local density enhancements around the pyrene solute, defined as the local density divided by the bulk density, are also included in Table I. These local density enhancements will be used later for direct comparison with simulation results. 

Pyrene Solution Preparation. Pyrene was purchased fi om Aldrich Chemical Company and used directly. A phosphate buffer, pH 6 upon dilution was used (6). For the fluorescence quenching experiments an aqueous pyrene stock solution was prepared fi-om a 2.05 x 10" solution of pyrene in methanol 1.5 ml of the methanolic pyrene solution was mixed with 498.5 ml of pH 6 buffer water to give a concentration of 6.15 X 10" M aqueous pyrene. The pyrene fluorescence intensity tended to be more stable if the solution were allowed to mix 1 hour before use. 

Mice chronically administered a 10% pyrene solution throughout their lifetimes did not develop skin tumors (Wynder and Hoffmann 1959a). However, prolonged dermal exposure of mice to 0.5% pyrene in decalin/n-dodecane solvent produced a slightly elevated (15%) skin carcinoma incidence the level of statistical significance was not provided (Horton and Christian 1974). 

The classic example for the tt-tt electron interaction between polycyclic arenes is the pyrene excimer (11). Upon UV excitation of a 10 5 M pyrene solution, the structured fluorescence of monomeric pyrene molecules is mainly observed. The increase of the concentration to 10 3 M diminishes the monomeric fluorescence, and a new broad and completely structureless excimer band appears, which is red-shifted by 5000-6000 cm-1. This phenomenon can be explained through potential curves of the electronic ground state and the excited singlet state (I, 12). The spectroscopic shift between the fluorescence of the excimer and the monomer depends on the depth of the potential well in the excited state that is, the red shift is proportional to the binding energy of the excimer. 

The addition of 5 x 10 M nonionic surfactant (Brij, Triton, Igepal) to a pyrene solution containing 2 x 10 M p-, y-, or dimethyl-/ -CD increased, in some cases remarkably, the 13 lifetime. Minor effects, and in some cases reduction of the lifetime, were found with dimethyl-/J-CD. The CMC value increased in the presence of the dextrins, indicating an interaction between the surfactant and the CD. The coinclusion of 13 and the aliphatic moiety of the surfactant in the CD cavity may explain the variations in pyrene lifetime [120]. 

Pyrene Monomer and Excimer Emission. The emission of locally isolated excited pyrenes ( monomer emission, intensity Im) is characterized by a well-resolved spectrum with the [0, 0] band at 378 nm. The emission of pyrene excimers (intensity Ie), centered at 480 nm, is broad and featureless. Excimer formation requires that an excited pyrene (Py ) and a pyrene in its ground state come into close proximity within the Py lifetime. The process is predominant in concentrated pyrene solutions or under circumstances where microdomains of high local pyrene concentration form, even though the total pyrene concentration is very low. This effect is shown for example by... 

When the host is fluorescent-inactive and the gradual addition of host upon a pyrene solution results in both dynamic and static quenching, the Stem-Volmer description of the observed fluorescence intensity ratio FIFq can be defined by Eq. (13.10) ... 

In order to explore the interactions between calixarene and SAIL, we next used fluorescence from pyrene as the indicator. The concentration of the three calixarenes, (1), (2), and (3), respectively, were varied within the pyrene solution in 1M aqueous NaOH in the presence of 50mM (post-cmc) concentration of SAIL [Cj(,mim][Cl]. We extracted information from both pyrene polarity scale and the changes in the fluorescence signal of the pyrene as the concentration of the calixarene is changed. 

Birks JB, Munro IH, Dyson DJ (1963) Excimer fluoresctaice. 2. Lifetime studies of pyrene solutions. Proc R Soc Lond Ser A Math Phys Sci 275(1360) 575-588. doi 10.1098/rspa. 1963. 0187... 

Fig. 5.32 UV-vis spectra of pyrene solutions solubilized by a PS-PAA-PS, b HB-(PAA)io-g-(PS)n and c HB-(PAA)47-g-(PS)4g chains with different concentrations...

In 1954 Forster and Kasper discovered that when the concentration of pyrene solutions was increased a new structureless emission band appeared, red-shifted to the normal pyrene emission, which decreased in intensity (31). Since the absorption spectrum was found to be independent of concentration, the new emission was ascribed to a complex of an excited and a ground-state pyrene molecule. Similar phenomena were soon noted with other aromatic molecules. In the crystalline state, an emission characteristic of the excited dimer ("excimer") was observed only when the molecules lay face-to-face at a distance of about 0.35 nm (32) and it was concluded that this is the geometry required for excimer formation. 

Steady-state fluorescence spectra were recorded on a Hitachi F-4500 fluorescence spectrophotometer. Emission spectra of pyrene probes were measured with excitation at 337 nm at room tenq)erature. Excitation spectm were monitored at 372 nm. Sample solutions were prepared by dissolving a predetermined amount of polymer in an aqueous pyrene solution of a known concentration, and the solutions were allowed to stand for 1 day for equilibration... 

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