Pyrene, lifetimes

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]. 

Samples for studies of CDx effects on fluorescence enhancement in organic solution were prepared using pyrene, because pyrene possesses a long lifetime and is very susceptible to quenching and enhancement in solution (23). An aliquot of pyrene stock solution in cyclohexane was placed under a nitrogen purge to evaporate the cyclohexane. Samples were redissolved in a 1 A mixture of Isopropyl ether and 1-butanol, which was saturated with aqueous CDx solution. Pyrene samples were also prepared in which the organic solvent was not saturated with CDx solution. The mixed solvent was used in order to minimize the effects of ether evaporation and thus allow more accurate quantitation. Fluorescence measurements were made on diluted samples of these solutions. The solvent used to make up the... 

The first observations of P-type delayed fluorescence arose from the photoluminescence of organic vapors.<15) It was reported that phenanthrene, anthracene, perylene, and pyrene vapors all exhibited two-component emission spectra. One of these was found to have a short lifetime characteristic of prompt fluorescence while the other was much longer lived. For phenanthrene it was observed that the ratio of the intensity of the longer lived emission to that of the total emission increased with increasing phenanthrene vapor... 

We find that the fluorescence yield of freshly prepared covalent (+)-anti-BaPDE-DNA adducts in oxygen-free solutions is 66+2 lower than the yield of the tetraol 7,8,9,10-tetrahydroxytetrahydro-benzo(a)pyrene (BaPT) in the absence of DNA. Since the fluorescence lifetime of BaPT under these conditions is 200ns, the mean fluorescence lifetime of the adducts (see reference T7) can be estimated to have a lower limit of 3ns, which is close to the mean value of 0.52x1.6 + 0.42x4.0 = 2.7 ns estimated from the two short fluorescence components of Undeman et al (10). 

Lochmuller and coworkers used the formation of excimer species to answer a distance between site question related to the organization and distribution of molecules bound to the surface of silica xerogels such as those used for chromatography bound phases. Pyrene is a flat, poly aromatic molecule whose excited state is more pi-acidic than the ground state. An excited state of pyrene that can approach a ground state pyrene within 7A will form an excimer Pyr +Pyr (Pyr)2. Monomer pyrene emits at a wavelength shorter than the excimer and so isolated versus near-neighbor estimates can be made. In order to do this quantitatively, these researchers turned to measure lifetime because the monomer and excimer are known to have different lifetimes in solution. This is also a way to introduce the concept of excited state lifetime. 

P-type delayed fluorescence is so called because it was first observed in pyrene. The fluorescence emission from a number of aromatic hydrocarbons shows two components with identical emission spectra. One component decays at the rate of normal fluorescence and the other has a lifetime approximately half that of phosphorescence. The implication of triplet species in the mechanism is given by the fact that the delayed emission can be induced by triplet sensitisers. The accepted mechanism is ... 

Montalti and co-workers studied dansyl [27] and pyrene [28] derivatives and found the fluorescence quantum yields and excited-state lifetime of these two dyes increased in DDSNs. They attributed the enhancements to the shielding effect from the quenchers or polar solvent in the suspension. Their studies also demonstrated that the lifetime of the doped dye molecules was also dependent on the size of the DDSNs. Small DDSNs had a larger population of the short-living moieties that were more sensitive to the environment outside the DDSN. In contrast, the large DDSN had a larger population of the long-living moieties that were not sensitive to the environment. 

Triplet-triplet annihilation In concentrated solutions, a collision between two molecules in the Ti state can provide enough energy to allow one of them to return to the Si state. Such a triplet-triplet annihilation thus leads to a delayed fluorescence emission (also called delayed fluorescence of P-type because it was observed for the first time with pyrene). The decay time constant of the delayed fluorescence process is half the lifetime of the triplet state in dilute solution, and the intensity has a characteristic quadratic dependence with excitation light intensity. 

DIPHANT, and 5 x 106 s 1 for pyrene-based bifluorophores (whose lifetimes are of the order of 200 ns). 

A description of a fast laser photolysis experimental arrangement has been given by Porter and Topp who used a 1.5 Joule, 20nsec ruby giant pulse, frequency doubled in ADP, to measure singlet lifetimes in phenantrene, pyrene and other organic molecules. 

Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of lOOA. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micro-polarity as a function of distance from the polar core of these Inverted micelles. Pyrene exclmer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively. 

In order to test further the applicability of 1-pyrene carboxaldehyde as a fluorescent probe, we applied Keh and Valeur s method (4) to determine average micellar sizes of sulfonate A and B micelles. This method is based on the assumption that the motion of a probe molecule is coupled to that of the micelle, and that the micellar hydrodynamic volumes are the same in two apolar solvents of different viscosities. For our purposes, time averaged anisotropies of these systems were measured in two n-alkanes hexane and nonane. The fluorescence lifetime of 1-pyrene carboxaldehyde with the two sulfonates in both these solvents was found to be approximately 5 ns. The micellar sizes (diameter) calculated for sulfonates A and B were 53 5A and 82 lOA, respectively. Since these micelles possesed solid polar cores, they were probably more tightly bound than typical inverted micelles such as those of aerosol OT. Hence, it was expected that the probe molecules would not perturb the micelles to an extent which would substantially affect the micellar sizes measured. 

Polarity Variation in Sulfonate Micelles. Other workers have established a correlation between the fluorescence lifetime of pyrene in solution and the polarity of the solvent medium (9). Polar media quench the excited electronic state of pyrene and hence shorten its fluorescence lifetime. We applied this principle to measure the polarity variation within the micelles of sulfonates A and B. 

Figure 5. Plots of the fluorescence lifetime of pyrene as a function of distance from the polar core of the micelles of sulfonates A and B in heptane solutions.

Pyrene carboxaldehyde has utility as a fluorescent probe in some Inverted micellar systems containing solubilized Inorganic species in the polar core. Its fluorescence lifetime is ca. 5 ns thus it is an appropriate probe for measuring micellar sizes which are approximately lOOA. 

Whether or not a given PAH exists virtually entirely in the gas phase or in the particle phase, or is partitioned between them, is a critical factor in determining its physical and chemical fates in ambient air and in subsequent intra- and intermedia transport through our air/water/soil environments. This is true not only for physical processes such as wet and dry deposition but also for their chemical reactivity, lifetimes, and fates in VOC-NOx systems characteristic of polluted airsheds. For example, the homogeneous gas-phase reactions of pyrene and fluoranthene differ dramatically from the rates, mechanisms, and products of their particle-associated heterogeneous reactions (Sections E and F). 

Attack by OH radicals on the gas-phase fluoranthene and pyrene must be fast. As seen in Table 10.35, again this is true. In Table 10.36, the calculated atmospheric lifetimes of selected gas-phase PAHs due to reaction with OH are shown, e.g., lifetimes of 2.9 h for fluoranthene and pyrene. 

---