Pyrene In Solution Research Articles

Reaction yield detected magnetic resonance in exciplex systems

Reaction yield detected magnetic rescnance (RYDMR) experiments are reported from separate solutions of pyrene in the presence of different electron acceptors, the three isomers of dicyanobenzene, and the electron donors, N,N-dimethyl- and N,N-diethyl-aniline. For the first time a complete set of RYDMR B 0 and B 1 spectra are provided from radical pairs in low viscosity organic solvents. The data are of high quality, due to apparatus development, and provide detailed insight into the processes occurring within the radical pair. The results have been interpreted using a stochastic Liouville equation to account for the simultaneous action of spin and molecular dynamics within the spin correlated radical pair. Two different models of the latter have been used, a simple exponential one, which allowed the influence of the electron spin exchange interaction to be investigated, and a full diffusional one, with and without a potential between the radicals. In the dicyanobenzene systems, the RYDMR behaviour is shown to be dominated by spin mixing under the influence of the hyperfine interactions, although the fit to experimental data is improved if the Coulombic interaction between the radical ions, and the exchange interaction, are taken into account. In the dimethylaniline case, the effect of the exchange interaction seems considerable, and the behaviour is also affected by degenerate electron hopping between the cation and the parent molecule. Analysis gives the rate of this process, and allows an estimate of the lifetime of the geminate radical pair in this system. This appears to be in the region of 60 to 300 ns, and is remarkably long. Theory also indicates that the effect of relaxation due to electron spin exchange processes may be significant in RYDMR measurements, particularly those performed in the higher microwave fields, or in viscous media. A method for calibrating the microwave field in the resonant cavity from a comparison of RYDNR and magnetic effect on reaction yield (MARY) results from the same experimental system is described.

The influence of solvent on labelled and free pyrene aggregation in novolac solutions and films

The effects of various casting parameters were measured for films of novolacs (cresol-formaldehyde resins) containing pyrene groups either covalently bound to the polymer chain or physically dispersed in the novolac matrix. Aggregation of the dispersed pyrene was observed, as measured by excimer fluorescence and crystallite formation of the pyrene. The phase separation was enhanced in static-cast films over spin-cast films. Pyrene aggregation in films was also affected by the choice of casting solvent even though no significant solvent effects were observed for the tagged polymer or free pyrene in solutions of the casting solvents. A minimum in the plot of the excimer-to-monomer ratio for the films versus the dipole moment of the casting solvent occurred at about the dipole moment expected for the novolac. Pyrene aggregation appears to be more dependent on the interactions of the casting solvent and the host polymer rather than on the interaction of either with the pyrene itself.

Potentiation of the cage effect in binary solvents detected by magnetic modulation of exciplex fluorescence

It was shown that selective solvation potentiates the cage effect in recombination of radical ion pairs formed in electron phototransport in binary solvents with components with strongly differing dielectric properties. This is manifested by a more pronounced (in comparison to single solvents) increase in the exciplex fluorescence in a magnetic field in solutions of pyrene with an excess of N,N-dimethylaniline. The magnitude of the magnetic effect, which is a function of the composition of the solvent, is equal to a maximum of 18% (B= 30 mT) for the benzene/dimethyl sulfoxide binary solvent with a 0.26 volume fraction of the latter. A simple model which explains the results obtained is proposed.

Time-resolved fluorescence studies of the intermolecular excimer formation of pyrene in solution under high pressure

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTime-resolved fluorescence studies of the intermolecular excimer formation of pyrene in solution under high pressureMasami Okamoto and Muneo SasakiCite this: J. Phys. Chem. 1991, 95, 17, 6548–6553Publication Date (Print):August 1, 1991Publication History Published online1 May 2002Published inissue 1 August 1991https://doi.org/10.1021/j100170a033RIGHTS & PERMISSIONSArticle Views118Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (648 KB) Get e-Alerts

Complete spectra of the delayed luminescence from aromatic compounds in liquid solutions: On the observability of direct radiative triplet-triplet annihilation

With many aromatic compounds in liquid solution, the population of the metastable triplet state T 1 leads to delayed S n →S 0 fluorescence (DF n, n⩾ 1) of the pyrene type, which results from the generation excited singlet states S n by nonradiative triplet-triplet annihilation (TTA) T 1 + T 1 ⇝ S n + S 0. Knox and Swenberg have postulated that, apart from the DF1, there should be an extremely weak direct radiative TTA: T 1 + T 1 → S 0 + S 0 + hν rad. The spectrum of the direct radiative TTA is likely to be si the convolution of the phosphorescence spectrum with itself. Due to this similarity, part of the high-energy delayed luminescence from solutions of pyrene and phenazine can be assigned to direct radiative TTA. The probability of direct radiative TTA relative to the generation of S n by nonradiative TTA is typically ≲ 5 × 10 −7. With anthracene, 9-methylanthracene and 1,2-benzanthracene no similarity has been found between the spectrum of the observed high-energy luminescence and the calculated spectrum of radiative TTA. Some special aspects of the delayed fluorescence are treated: nonradiative TTA as a special case of Dexter energy transfer, the temperature dependence of the delayed excimer fluorescence from pyrene, nonequilibrium hot-band delayed fluorescence from S 1 of anthracene, and the problem of the indirect determination of lifetimes of upper excited singlet states.

ChemInform Abstract: Spectral Evidence for Different Phases Exhibiting the Shpol′skii Effect in Concentrated Solutions of Pyrene and Dibenzofuran in Frozen n‐Alkanes.

ChemInform Abstract: Spectral Evidence for Different Phases Exhibiting the Shpol′skii Effect in Concentrated Solutions of Pyrene and Dibenzofuran in Frozen n‐Alkanes.

Spectral evidence for different phases exhibiting the Shpolskii effect in concentrated solutions of pyrene and dibenzofuran in frozen n-alkanes

Spectral evidence for different phases exhibiting the Shpolskii effect in concentrated solutions of pyrene and dibenzofuran in frozen n-alkanes

Excimer formation of pyrene as a probe to investigate the recombination of geminate pairs: ODESR and fluorescence study of dilute pyrene in squalane

It is shown that the monomer fluorescence and the excimer fluorescence from a dilute pyrene solution in squalane at room temperature are mainly from “delayed” geminate pairs (Py −, S +) and (Py −, Py +), respectively, from the ODESR spectra observed at the monomer and the excimer fluorescence. The recombination time of the former pair is found to be much shorter than that of the latter from analysis of these ODESR amplitudes. This indicates that the hole (S +) hops between the solvent molecules towards the solute anion.

Pulse radiolysis studies on the transient species of aromatic molecules in chlorinated hydrocarbon solutions

Pulse radiolysis has been carried out to identify the transient species produced by the pulsed electron irradiation for the several kinds of combination of the solutions of aromatic hydrocarbons (benzene, naphthalene and pyrene) in chlorinated hydrocarbons (CCl 4, CHCl 3, and CH 2Cl 2). Charge-transfer complex between aromatic ring and Cl atom has been observed for benzene solutions in above three solvents. Naphthalene monomer and dimer cation radicals have been observed for the solutions in CHCl 3 and CH 2Cl 2. Monomer cation radicals of pyrene has been observed for the solution of pyrene in CCl 4, and monomer and dimer cation radicals of pyrene have been observed for the solutions in CHCl 3 and CH 2Cl 2.

Time-resolved fluorescence spectroscopy of crude oils and condensates

A pulsed laser fluorescence spectroscopy system, previously developed for coal characterization, was used to characterize thirteen crude oils and condensates. From time-resolved fluorescence spectra, three individual components (fluorophores) with decay times in the nanosecond and sub-nanosecond range were resolved. A good correlation was obtained between the fluorescence decay times of these components and API gravity. The fluorescence decay of normal crude oil was different from biodegraded crude oil. Two of the three resolved component spectra and decay times resembled those of anthracene and pyrene in solution.

Observation of resonance Raman spectra of S 1, T 1, and S 0 pyrene in solution: Application of a fluorescence rejection technique

The new technique of fluorescence rejection during Raman measurements was applied to observe transient resonance Raman (RR) spectra ofpyrene in electronically excited states and a UV RR spectrum in its ground state. The method gave well-defined spontaneous RR spectra with a nanosecond source despite the strong fluorescence.

Porphinatoiron-mediated oxidation of polycyclic aromatic hydrocarbons

Although porphinatoiron complexes have been used extensively as biomimetic catalysts for oxidation of aliphatic and olefinic hydrocarbons, few oxidations of polycyclic aromatic hydrocarbons (PAH) have been reported. In all cases, heterogeneous iodosobenzene/tetraphenylporphinatoiron(III) systems were employed, oxidations were inefficient and control experiments demonstrating the requirement for catalyst were not described. The current study investigates the oxidation of pyrene, benzo[ a]pyrene and benzanthracene in a homogeneous m-chloroperoxybenzoic acid/bifacially hindered porphinatoiron system in which the peroxyacid was shown to be unreactive in the absence of catalyst. Pyrene and benzo[ a]pyrene were oxidized efficiently, with pyrene yielding mixtures of 1,6- and 1,8-quinones and benzo[ a]pyrene yielding mixtures of phenols and quinones. Benzanthracene was oxidized less efficiently, primarily at the meso positions, to give 7,12-quinone. Initial oxidation of meso carbons of benzo[ a]pyrene (confirmed by the presence of the 6-hydroxy derivative as a product) and benzanthracene indicates that PAH-to-catalyst charge transfer may be an important oxidation pathway. Oxidation of pyrene was performed by addition of pyrene to observable oxo iron(V) species as well as in a catalytic reaction where excess peroxyacid was added to a solution of pyrene and catalyst and oxo iron(V) is not generated as an observable intermediate. Yields (based on oxidant consumed), were identical under both conditions, strongly supporting oxo iron(V) as a common intermediate.

The toxicity of pyrene in the fish [formula omitted][formula omitted]: Synergism by piperonyl butoxide and by ultraviolet light

A saturated solution of pyrene in water was not toxic to the fish Pimepnales promelas , even in the presence of ultraviolet light. A survival curve possessing one minimum, and therefore defining two LC 50 values, was obtained when fish placed in water containing increasing amounts of a pyrene solution in dimethylsulfoxide were exposed to ultraviolet light after a short incubation period. The phototoxicity was linked to the presence of undissolved pyrene. A normal survival curve with only one LC 50 value was found when pyrene was solubilized with the surfactant Tween-20. Practically no phototoxicity was produced when the pyrene mixtures were filtered before use, or when a saturated aqueous solution of pyrene was used. Piperonyl butoxide, present at a concentration where it was not toxic, synergized the toxicity of pyrene in the dark . The environmental significance of this observation may be considerable.

Electron-donor–electron-acceptor association constants of pyrene with 2,4,6-trinitrotoluene in solution determined by 1H-nuclear magnetic resonance from non-linear Scatchard plots

The chemical shifts of the ring and methyl protons of 2, 4, 6-trinitrotoluene have been measured as a function of the concentration of added pyrene in solutions in carbon tetrachloride at 33.5 °C. Simple analysis at the 95 % confidence level yields association constants K= 8.42 ± 0.1 and 7.92 ± 0.1 kg mol–1 from these two probes, respectively. Allowance for ‘additional unspecific shielding’ increases these values to K= 9.10 ± 0.05 and 8.84 ± 0.06 kg mol–1. Alternatively, analysis based on a double equilibrium forming complexes with stoichiometry DA and D2A results in association constants K1= 8.7 ± 0.2 and 8.4 ± 0.3 kg mol–1, and K2= 0.23 ± 0.05 and 0.31 ± 0.07 kg mol–1 from HAr and HMe, respectively. Thus, whilst the model of a simple 1:1 association is untenable, the data do not provide a clear choice between the second and third models in this particular system.

Dynamics of geminate ions in the pulse radiolysis of cyclohexane and n-hexane containing aromatic solutes studied by streak camera measurements of fluorescence and absorption

The nature of geminate ion reactions in cyclohexane or n-hexane solutions irradiated with 30 ps electron pulses has been investigated by observing solute excited state fluorescence and absorption of solute ions. For the fluorescence measurements, 4-Br,4″hexa(5-decyl)- p-terphenyl(BHTP) was used as the solute. The short fluorescence lifetime (0.3 ns) of the excited singlet state of this compound (BHTP 1) facilitates the interpretation of the results because BHTP 1 formed in an excitation process occuring during the pulse decays rapidly enough that the slower production of BHTP 1 by reaction of BHTP ⨪ with the radical cation of the solvent is more easily discernible than in the case of scintillators with longer lifetimes. Comparison of the results with a model indicates a qualitative correspondence with the known properties of ions and electrons in the two solvents. In particular, the results support a higher mobility cation derived from the solvent in cyclohexane, compared with n-hexane. Quantitatively, however, the experimental data show a greater amount of excitation occuring within the first 20 ps (during the pulse) than is expected from the model. Results on the formation of the pyrene radical cation in cyclohexane and n-hexane solutions of pyrene also show significant differences between the two solvents which indicate a slower formation of the pyrene cation in n-hexane.

Quenching of excited states of pyrene sulfonate solutions and their metal complexes by molecular oxygen

The results of study of fluorescence quenching, by molecular oxygen, of unsubstituted pyrene solutions within the framework of exchange complex are generalized. The oxygen quenching rate constants of the fluorescence and triplet state of pyrene monosulfonate and pyrene tetrasulfonate solutions and their aggregates and complexes (second and first coordination spheres) with REE ions in H2O, DMSO, and DMFA are measured. The effect of the number of substituting sulfo groups, aggregates, complex formation, and the nature of the solvent on the efficiency of this quenching is investigated. It is shown that, in contrast to metalloporphyrins with the paramagnetic Cu(II) ion, the formation of pyrenesulfonates complexes with REE paramagnetic ions does not lead to an increase in oxygen quenching efficiency of the triplet state of organic ligands.

Picosecond Absorption Spectra and Relaxation Processes of the Excited Singlet State of Pyrene in Solution

The method of analysis for the ps transient absorption spectra obtained by a ps Nd3+: YAG laser photolysis system is described in detail, showing the results of pyrene in solution. The Sn ← S1 spectrum observed immediately after excitation is rather broad and its intensity in the short wavelength region is relatively enhanced, compared to the spectrum observed at later stages. For elucidating this fast spectral change, the spectrum at 0 ps was simulated from that at 100 ps, evaluating numerically the inner filter effect, depletion of the ground state molecules and temporal characteristics of the monitoring ps continuum. The difference between the simulated and experimentally observed spectra may be ascribed to the nonlinear refractive index change of the solvent, the thermal lensing effect, or to an intrinsic relaxation of the excited molecule. Examining absorption spectra obtained under various conditions, the former two possibilities were denied for the excited pyrene system. Vibrational relaxation as well as the S2 → S1 internal conversion with a time constant of less than 10 ps have been suggested to be responsible for this difference between the simulated and observed spectra.

Fluorescence and induced circular dichroism studies on host–guest complexation between γ-cyclodextrin and pyrene

Host–guest complexation between γ-cyclodextrin (γ-CD, cyclo-octa-amylose) and pyrene has been studied in detail by fluorescene and induced circular dichroism (i.c.d.) spectra. γ-CD forms complexes with pyrene with 1 : 1, 1 : 2, 2 : 1, and 2 : 2 stoicheiometries at ambient temperature. The inclusion of pyrene by γ-CD proceeds stepwise; γ-CD including only one pyrene molecule can accommodate a second pyrene molecule to produce a 1 : 2 and/or 2 : 2 complex. Both in a monomolecularly dispersed pyrene solution and in a suspended pyrene solution, several hours are required for γ-CD to include two pyrene molecules. The configuration of two pyrenes included is an S-helix. At temperatures above ca. 85 °C, a 1 : 1 complex alone is formed mainly, where a pyrene molecule is accommodated with its long axis parallel to the axis of γ-CD. The data are compared with those of the systems containing β-CD (cyclohepta-amylose) in place of γ-CD.

The formation of solute excited triplet states via geminate ion recombination in cyclohexane solutions of biphenyl and pyrene on subnanosecond and nanosecond timescales

The formation of the solute excited triplet states via geminate ion recombination observed for both biphenyl and pyrene solutions in cyclohexane has been studied by using a picosecond pulse radiolysis system for absorption spectroscopy with the time resolution of 8o ps. The ratio of the formation rate of the solute excited triplet state of the decay rate of the solute anion changes in a time range between 5 and 20 ns. It is very well correlated with the spin correlation decay of geminate ion pairs, which are initially paired with each other in a singlet state. The formation of the solute triplet state was observed even on a timescale shorter than 5 ns, although loss of spin correlation is negligibly small.

Electric field quenching of fluorescence in the photoionization of solutes by far UV light

Measurement of the photocurrent and fluorescence of solutions of perylene, pyrene, triphenylamine and tetramethyl- p-phenylene-diamine as a function of applied electric field were made for far UV excitation between 180 and 210 nm. The ratio of the change in fluorescence (Δ F) to the fluorescence at zero field increases linearly with the photocurrent. Quantum yields of ionization (φ e) and of ion-pair formation (φ ip ) are derived from the data. The results show that ionization becomes increasingly important for the solutes studied at wavelengths below 210 nm where ion pair yields in some cases approach 40%. In general, ionization yields determined by the electric field quenching of fluorescence technique agree with direct photocurrent measurements using actinomentry. Some differences are observed, however, which are attributed to decomposition channels which can be important for the higher photon energies in the vacuum UV.