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• 129-00-0 pyrene 
• 123-03-5 cetylpyridinium chloride 

Relevant academic research and scientific papers

Fluorescence Study of Pyrene and Naphthalene in Cyclodextrin-Amphiphile Complex Systems

Amphiphilic molecules are shown to interact with pyrene-β-cyclodextrin (Py-β-CD) complexes leading to an extremely hydrophobic environment for pyrene (Py) in aqueous solution.The three-component systems give rise to a 1:1:1 complex of Py, β-CD, and the surfactant.The binding constant of Py and β-CD increases significantly in the presence of the surfactants, which suggests an improvement in the solubility of Py in aqueous β-CD systems.Larger binding constants of Py and β-CD were obtained in the presence of shorter chain amphiphiles between C4 and C16 surfactants.Fluorescence quenching of Py in Py-β-CD-pyridinium surfactants (CnPd(1+)x(1-)) systems obeyed first-order kinetics, which were independent of the concentration of CnPd(1+)X(1-) above a certain concentration, while the quenching rate constant was markedly affected by the chain length of the pyridinium surfactants.Smaller rate constants are obtained for longer chain surfactants.The observed kinetics are explained in terms of a 1:1:1 complex formation of Py, β-CD, and CnPd(1+)X(1-), and the chain-length-dependent rate constants are interpreted by assuming a "diffusion-controlled reaction within limited space".On the other hand, Stern-Volmer kinetics were observed for Py fluorescence quenching in the Py-β-CD-C16C2V(2+) (1-ethyl-1'-hexadecyl-4,4'-bipyridinium ion) system.This is ascribed to the long-range nature of the reaction in Py(S*1)-viologen group systems compared with that in Py(S*1)-pyridinium group systems.In the naphthalene-β-CD (N-β-CD) system, reduced association constants were observed in the presence of surfactants, which is markedly different from that observed in the Py-βCD system.A determination of the dynamic parameters of the equilibrium showed that the entry rate constant of naphthalene into β-CD was reduced in the presence of surfactants, while the exit rate constant was unchanged.The exit rate was appreciably reduced in the Py-β-CD system on addition of surfactants.Quenchers such as oxygen, nitromethane, copper(II) ion, thallium(I) ion, etc., which reside in the aqueous phase also quench excited Py in β-CD.The influence of CD with and without surfactant on the rate depends on the nature of the quenching reaction, and on the degree of screening by the host system on the guest molecule.It is demonstrated in the present study that the introduction of amphiphilic molecules into the Py-β-CD complex system improves the organization of the system and simplifies the reaction mechanism.The unique types of reaction kinetics observed are due to the selective organization of reactants in the CD system.

Photophysical Properties of Pyrene in Zeolites: A Direct Time-Resolved Diffuse Reflectance Study of Pyrene Anion Radicals in Zeolites X and Y

The formation of pyrene anion radicals (Py.-) in the supercage of different alkali-ion-exchanged zeolites X and Y was studied using direct time-resolved diffuse reflectance techniques.Many factors such as the Si/Al ratio, the nature of charge balancing cations, the preactivation temperature, the pyrene loading, the state of hydration, and the nature of the surfaces (external versus internal) were examined in order to understand the formation and stabilization of Py.- in these samples, and also the mechanism of the photoinduced electron transfer processes.The results show that photoinduced electron transfer does not occur from pyrene to pyrene in the zeolites but occurs between pyrene molecule and the acidic and basic sites of the zeolites.The basic sites of the zeolites, responsible for the formation of Py.-, are framework oxygen.Stabilization of Py.- requires the special environment of the zeolite supercage; it is noteworthy that Py.- cannot be formed on the external surface of a zeolite.The formation of Py.- in the different alkali-ion-exchanged zeolites X- and Y follows the order of basicity of these samples, which is calculated using the Sanderson electronegativity equalization principle.Preactivation of the samples at temperatures of 350, 550, and 750 deg C does not affect the ratio of the anion to cation, Py.-/Py.+, yields.Posthydration of the samples alters the photophysical processes in the zeolites and gives rise to an increase in the yield of Py.-.At low light intensities, the photoinduced electron transfer follows a single-photon increase in the yield of Py.-.At low light intensities, the photoinduced electron transfer follows a single-photon mechanism.

Mobilities of Radical Cations and Anions, Dimer Radical Anions, and Relative Electron Affinities by Times of Flight in n-Hexane

The mobilities of several radical cations and anions are measured in n-hexane using a thin-sheet time-of-flight (TOF) technique.We observe the radical cations of N,N,N',N'-tetramethyl-p-phenylenediamine, zinc tetraphenylporphine, and pyrene and the radical anions of perfluorobenzene, p-benzoquinone, anthraquinone, chloranil, buckminsterfullerene (C60), and octafluoronaphthalene.For all electron acceptors but C60, the dependence of the anionic TOF on acceptor concentration reveals the appearance of the homodimer radical anion at sufficiently high concentrations.The equilibrium constant for the monomer anion/monomer acceptor association reaction is obtained from the concentration studies.A Born-Haber cycle is then applied to estimate the difference between the electron affinities of the monomer and dimer molecules in the gas phase.

Photochemistry of Stilbene Adsorbed on Silica Gel and NaX Zeolite. A Diffuse Reflectance Laser Flash Photolysis Study

Diffuse reflectance laser flash photolysis (266, 308, or 355 nm) of either cis- or trans-stilbene (St) adsorbed on silica gel or included in NaX zeolite leads to the formation of the trans-St radical cation with λmax at 475 nm at high laser powers.At low laser intensities trans-St also yields radical cation while cis-St photocyclizes to give dihydrophenanthrene with λmax at 450 nm.In contrast to the results for irradiation of stilbene alone on solid supports, irradiation of the cis-St/TNM charge transfer complex on silica or zeolite leads to a mixture of both trans- and cis-St.+ (λmax at 510 nm), demonstrating that the cis radical cation is stable with respect to isomerization on these two solids.This result, in combination with product studies which demonstrate that there is substantial cis-trans isomerization within a single laser pulse, leads to the conclusion that the formation of trans-St.+ following laser irradiation of cis-St occurs via cis-trans isomerization followed by photoionization of trans-St.Laser irradiation of St or pyrene on NaX zeolite results in strong transient signals in the 500-600 nm region due to trapped electrons, in addition to the signals due to radical cations.The effects of both water and oxygen on the trapped electron and radical cation have been examined.The trapped electron can be photobleached with a second 532 nm laser pulse.The bleaching does not lead either to trapping of the electron by ground state aromatic to give its radical anion or to recombination with the radical cation to regenerate the starting material.This suggests that irradiation leads to a redistribution of the electron to other zeolite sites.

Surfactant-Concentration Effects in Photoinduced Electron Transfer from Pyrene to Cupric Ions in Sodium Dodecyl Sulfate Micelle Solutions

The decay of pyrene fluorescence and the quantum yield of pyrene cations were measured by using the laser photolysis method in sodium dodecyl sulfate (SDS) micelle solutions containing both pyrene and cupric dodecyl sulfate at 40 deg C.The decay curve of the pyrene fluorescence deviates from the first-order rate law at SDS concentrations below 0.2 M, as alredy known, but becomes first order at higher SDS concentrations.The rate shows incontinuity between 0.2 and 0.5 M SDS.The cation quantum yield remarkably increases with the SDS concentration: For 10 mM of cupric ion, the quantum yields were 0.25 and 0.60 at SDS concentrations of 0.05 and 0.8 M, respectively.These results can be explained in terms of involvement of large rodlike micelles in which the portion of the net electron transfer in quenching is larger than in usual spherical micelles.