Pyrene fluorescence-doping

In the present work, we have examined poly(N-vinylcarbazole) (abbreviated hereafter as PVCz) and pyrene-doped poly(aethyl methacrylate) (PMMA) films by using a tine-resolved fluorescence spectroscopic aethod. Fluorescence spectra and their dynanic behavior of the forner fila were elucidated with a high intensity laser pulse and a streak camera, which nakes it possible to neasure dynaaics just upon laser ablation. This aethod reveals aolecular and electronic aspects of laser ablation phenomena (17). For the latter fila a laser pulse with weak intensity was used for characterizing the ablated and Basked areas. On the basis of these results, we demonstrate a high potential of fluorescence spectroscopy in aolecular studies on laser ablation and consider its mechanism. Experimental... 

Fluorescence Rise and Decay Curves. Both monomer and excimer fluorescence decay curves of the unirradiated film are nonexponential and the excimer fluorescence shows a slow rise component. This behavior is quite similar to the result reported for the PMMA film doped with pyrene. (23) A delay in the excimer formation process was interpreted as the time taken for the two molecules in the ground state dimer to form the excimer geometry. Dynamic data of the ablated area observed at 375 no (monomer fluorescence) and 500 nm (exciner fluorescence) are shown in Figure 5. When the laser fluence increased, the monomer fluorescence decay became slower. The slow rise of the excimer fluorescence disappeared and the decay became faster. 

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. 

An example of exciplex formation in the solid state may be afforded by perylene doped crystals of pyrene which emit a green structureless fluorescence in addition to the blue and orange-red excimer bands of pyrene and perylene, respectively. Hochstrasser112 has shown that the energy of the emitting species is consistent with that of a charge transfer complex of pyrene and perylene molecules in a bimolecular unit of the pyrene lattice. 

Johnson and Willson interpreted the main feature of the observations on solid polyethylene doped with aromatic solutes in terms of an ionic mechanism it was analogous to that proposed for irradiated frozen glassy-alkane-systems in which ionization occurred with G = 3 — 4 [96], The produced charged species, electron and positive hole, were both mobile as indicated by the radiation-induced conductivity. The production of excited states of aromatic solutes was caused mainly by ion-electron neutralization. The ion-ion recombination was relatively slow but it might contribute to the delayed fluorescence observed. On the basis of Debye-Simoluchovski equation, they evaluated the diffusion coefficients of the radical anion of naphthalene and pyrene as approximately 4 x 10 12 and 1 x 10 12 m2 s 1 respectively the values were about three orders of magnitude less than those found in typical liquid systems. 

To illustrate the capabilities of the system shown in Fig. 16.12, we present new, previously unpublished results from our laboratory. In Fig. 16.13, we illustrate results for three fluorescent probe molecules (pyrene, DCM [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran], and PRODAN [6-propionyl-2-(/V,/V-dimethylamino)naphthalene]) that were doped within a series of PFFA/Pluronic P104 BP blends. In the initial experiments, 16 BP formulations were prepared manually using micropipettes, while subsequent experiments utilized the ALHS to prepare 21 BP formulations. These formulations were spun cast into thin films employing quartz microscope slides as substrates. To characterize the local microenvironment surrounding each probe within a given formulation, steady-state fluorescence measurements using a conventional spectrofluorometer were performed. 

The luminescence of doped polymers still continues to attract interest. Dimethylterephthalate quenches the delayed fluorescence of polyvinylcarbazole containing pyrene and... 

Time dependent fluorescence depolarization is influenced by the exciton annihilation which occurs in confined molecular domains . Photoemission results from singlet exciton fusion as shown by the excitation intensity dependence which occurs in anthracene crystals. Reabsorption of excitonic luminescence is an effect which has been shown to occur in pyrene crystals. The dynamics of exciton trapping in p-methylnaphthalene doped naphthalene crystals involves phonon assisted detrapping of electronic energy. Ps time resolved spectroscopy was the experimental technique used in this work. 

A similar experiment was performed for the PMMA film doped with 1-ethyIpyrene. As shown in Fig. 7, fluorescence spectra were composed of a structured monomer and red-shifted broad excimer bands. As molecular diffusion during fluorescence lifetime is negligible in film, the latter band is due to the ground state dimer of pyrene which is easily formed under its high concentration. It should be notified that the fluorescence intensity ratio of the monomer to excimer emissions under the TIR condition is larger than that under the normal one. This may indicate that the pyrenyl concentration in the interface layer is also lower than that in the bulk. 

A scheme of the experimental setup is shown in Fig. 83, where a laser beam (355 nm, 3 ns) is directed from the rear of the target film onto the triazene polymer film (doped with pyrene) as shown in Fig. 82. The laser fluence was estimated by averaging the total energy of the incident beam over the irradiated area. The target films [poly(butyl methacrylate), PBMA, Tg=293 K and poly(ethyl methacrylate), PEMA, Tg=338 K] were characterized with a fluorescence microscope and a conventional spectrofluo-rometer. 

Total internal reflection fluorescence spectroscopic measurements have been carried out on pyrene-doped PHOST thin films, in which pyrene serves as a fluorescence probe to study inhomogeneous distribution of small molecules and hydrophobicity of the interface layer [497]. 

Excimer formation in pyrene doped silica glasses prepared by the sol-gel method was studied with a picosecond time-resolved fluorescence spectrophotometer (Yamanaka, 1991). In high dopant concentration ofpyrene, the picosecond time-resolved fluorescence... 

Pouxviel J.C., Dunn B., Zink J.I. Fluorescence study of aluminosilicate sols and gels doped with hydroxy trisulfonated pyrene. J. Phys. Chem. 1989 93 2134-2139 Preston D., Ponxviel J., Novinson T., Kaska W.C., Dunn B., Zink J.I. Photochromism of spiropyrans in aluminosilicate gels. J. Phys. Chem. 1990 94 4167-1172 Sakka, Sumio, Sol-Gel Science. Tokyo Aguneshofu-sha, 1988... 

Evidence for some ground state pyrene association was provided by Yamanaka et al. (6971) in doped Si02 thin films, based on time-resolved fluorescence spectroscopy. 

As an extension of studies in n-alkanes (Scheme 1), pyrene-doped polyethylene films have also been exposed to ionizing radiation.Polyolefins with fluorescent probes such as pyrenyl groups, selectively labeled at interior positions, have permitted the micromorphological consequences of several macro perturbations (e.g., film stretching) to be investigated. ... 

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