Excited Singlet State Of Pyrene Research Articles

Spacer Length Effect on the Photoinduced Electron Transfer Fluorescent Probe for Alkali Metal Ions

Abstract— We have synthesized four derivatives of aikyi pyrene covalently bonded to aza‐lS‐crown‐6 at the nitrogen position, Py(CH2)n, (n = 1–4), to study the effect of spacer length on the emission properties of pyrene fluorophore upon complication of alkali metal ions by the crown moiety. In the absence of alkali metal ions, the parent molecule is weakly fluorescent because its emission is partially quenched by photoinduced electron transfer (PET) from nitrogen lone pairs to the excited singlet state of pyrene. Complication of alkali metal ions (e.g. K+) by the crown moiety prevents the nitrogen lone pair from participating in PET and results in an enhancement in the observed emission from pyrene (fluorescent turn on). Because the PET effect could be exerted through bonds as well as space, its magnitude may show a dependence on chain length. We have examined the fluorescence behavior of these pyrene aza‐crown ether derivatives in the presence of alkali metal ions to determine the magnitude of such an effect and its impact on the sensitivity of the fluorescent probe for detection purposes. Our results indicate that maximum efficiency for PET between the pyrene moiety and aza‐crown ether is achieved when n ≤ 3.

Spacer Length Effect on the Photoinduced Electron Transfer Fluorescent Probe for Alkali Metal Ions

Abstract— We have synthesized four derivatives of aikyi pyrene covalently bonded to aza-lS-crown-6 at the nitrogen position, Py(CH2)n, (n = 1–4), to study the effect of spacer length on the emission properties of pyrene fluorophore upon complication of alkali metal ions by the crown moiety. In the absence of alkali metal ions, the parent molecule is weakly fluorescent because its emission is partially quenched by photoinduced electron transfer (PET) from nitrogen lone pairs to the excited singlet state of pyrene. Complication of alkali metal ions (e.g. K+) by the crown moiety prevents the nitrogen lone pair from participating in PET and results in an enhancement in the observed emission from pyrene (fluorescent turn on). Because the PET effect could be exerted through bonds as well as space, its magnitude may show a dependence on chain length. We have examined the fluorescence behavior of these pyrene aza-crown ether derivatives in the presence of alkali metal ions to determine the magnitude of such an effect and its impact on the sensitivity of the fluorescent probe for detection purposes. Our results indicate that maximum efficiency for PET between the pyrene moiety and aza-crown ether is achieved when n ≤ 3.

Mechanism of Pyrene Photochemical Oxidation in Aqueous and Surfactant Solutions

The photolysis of pyrene has been studied in water and in Brij 35 micellar media. Photolysis in both media lead to the formation of 1,6- and 1,8-pyrenequinones as stable products. The first step in the photochemical oxidation is proposed to involve an electron transfer from the excited singlet state of pyrene to molecular oxygen in a contact charge-transfer pair. The effects of oxygen and HgCl2 on the photolysis are interpreted as ruling out mechanistic involvement of a triplet state of pyrene. 1-Hydroxypyrene is identified as a product of the initial photochemical oxidation. In the optically dilute aqueous solutions, 1-hydroxypyrene undergoes further photochemical oxidation to produce 1,6- and 1,8-pyrenequinones. Pyrene photolysis quantum yields are decreased by a factor of approximately 2 in the micellar media relative to the quantum yields determined in water. Fluorescence data suggest that pyrene resides in the micelles among the polyoxyethylene portion of the surfactant and not within the core of the...

The Nitrogen-Laser Excited Luminescence of Pyrene: A Student Laboratory Study of Excimer Dynamics

An Undergraduate laboratory experiment that uses a nitrogen laser to produce the first excited singlet state of pyrene is described. The resulting luminescence is studied as a function of wavelength, time, and pyrene concentration to observe the dynamics of both the excited pyrene monomer and the pyrene excimer. The initial rise and subsequent decay of the excimer is directly observed. Data is analyzed in terms of coupled rate equations, and students obtain four different rate constants in interactive calculations. The apparatus is relatively easy to set up, and introduces students to a variety of topics in photochemical kinetics and fast measurement techniques.

Transient absorption and vibrational relaxation dynamics of the lowest excited singlet state of pyrene in solution

The spectrum of highly excited electronic states of pyrene in n-octane solution and the relaxation processes in the SI singlet state are investigated by femtosecond transient absorption spectroscopy. Three different UV excitation wavelengths (360, 307, and 290 nm) are utilized to excite the molecule at the edge of the SI - SO transition and to higher S, - SO transitions. The buildup of SI population has been observed to be completed in the first 2 ps, with a time constant of 300-400 fs, depending on the excitation wavelength. The evolution of the absorption spectra on a larger time scale is attributed to the vibrational cooling in the SI state; its rate corresponds to an exponential relaxation with time constant of about 4 ps. The evidence of the formation of pyrene excimer at long time delays in highly concentrated solutions is reported. The interaction of an intense short laser pulse with a molecule in solution leads generally to various photoproducts which relax differently through complex relaxation dynamics. The simplest process is the absorption of a single photon bringing the molecule to some excited vibronic level. The excited molecule undergoes then very fast nonradiative decay processes which eventually produce the buildup of an out-of-equilibrium vibrational population, normally in the SI state. Slower radiative and nonradiative processes, the latter involving mostly solutesolvent interactions, then relax the molecule to the ground state. Conformational changes can take place in parallel to the relaxation processes.' With intense light pulses, multiphoton excitation, ionization, and bond breaking may become competitive processes; in these cases new molecular species are produced, and new channels are made available for energy relaxation. The investigation of the excited states, of the possible photoproducts, and of the associated dynamical processes can be performed by means of several spectroscopic techniques such as transient absorption, transient Raman, and IR spectroscopy utilizing ultrafast laser source^.^.^ Transient absorption spectroscopy with subpicosecond resolution in the visible and near-W region is probably the most widely used and certainly the most feasible among these techniques. Transient absorption can be performed with two kinds of experimental configurations. The first one utilizes two monochromatic pulses at fixed wavelength: one (the pump) centered at the SI - SO transition (or at some higher resonance, from which population in the SI state is eventually produced) and the second (the probe) at the S, - SI transition. In this case the rise and the decay time of the transient absorption give information about the mechanism of population of SI and about the relaxation processes of this state toward the ground state. In the second experimental configuration, the S, - SI transitions (and, possibly, other transitions involving a higher starting level) are monitored by looking directly at the transient spectrum recorded at different delay times, using a white light probe pulse.

New functional polymers prepared by ring-opening metathesis polymerization: study of the quenching of luminescence of pyrene end groups by ferrocene or phenothiazine centers in the polymers

Emission from pyrene end-capped redox polymers is quenched relative to emission from l-vinylpyrene, a structural model for the end group in the polymer. The redox polymers were prepared by ring-opening metathesis polymerization (ROMP) of norbornene derivatives containing ferrocene or phenothiazine, using catalysts of the type Mo(CH-t-Bu)(NAr)(O-t-Bu)[sub 2] (Ar = 2,6-diisopropylphenyl). The pyrene group was introduced by reaction of the living polymer with l-pyrenecarboxaldehyde, thus producing polymers that are derivatives of l-vinylpyrene. A ferrocene-containing homopolymer was prepared with 12 equiv of a ferrocene-containing monomer, followed by capping with pyrene, (1)[sub 12]-pyrene, where pyrene emission is quenched by a factor of 30. Two phenothiazine-containing polymers were studied; a homopolymer prepared from 10 equiv of a phenothiazine-containing monomer followed by capping with pyrene, (2)[sub 10]-pyrene, and a block copolymer formed from 10 equiv of a phenothiazine monomer, then 70 equiv of norbornene, (NBE), followed by capping with pyrene, (2)[sub 10](NBE)[sub 70]-pyrene. In these polymers pyrene emission is quenched by a factor of 110 and 7, respectively. The quenching is proposed to occur via electron transfer from phenothiazine to the excited singlet state of pyrene and, depending on the structure of the polymer, by the formation of an exciplex with phenothiazine. 22 refs., 5more » figs., 2 tabs.« less

Photophysics studies of organic compounds VIII. Interaction between excited singlet state of pyrene and aromatic amines

AbstractThe quenching processes of the excited singlet state of pyrene by triphenylamine, diphenylamine and N,N‐dibenzylaniline in various solvents at room and lower temperature have been studied with both static state fluorescence spectroscopy and fluorescence lifetime techniques. On the basis of experimental data, a preliminary quenching mechanism has been discussed. The geometrical configuration models of the exciplexes formed between the excited pyrene and aromatic amines in nonpolar solvents were proposed.

The effect of caffeine on the reactions of the excited singlet state of pyrene in micellar sodium lauryl sulfate

The effect of caffeine on a few photo-induced reactions of pyrene in micellar sodium lauryl sulfate (NaLS) has been studied. In these systems caffeine complexes with the pyrene (K asso = 85 ± 10 M −1 and also with the other reactants, e.g. Cu 2+ or TI +. The efficiencies of reactions which involve contact, i.e. pyrene excimer formation, and quenching by TI + ions to give the triplet state of pyrene, are significantly reduced in the presence of caffeine, due to geometric inhibitions formed by the complexation processes. The kinetics of photo-induced electron transfer, e.g. between excited pyrene and Cu 2+, are not affected. However, the subsequent reactions of the products are modified and the yield of ionic products is markedly increased.

Reactions of the excited singlet state of pyrene with metal ions. Intermolecular electron transfer in caffeine-solubilized aqueous solution

Reactions of the excited singlet state of pyrene with metal ions. Intermolecular electron transfer in caffeine-solubilized aqueous solution

Effect ofcholinergic ligands on the lipids of acetylcholine receptor-rich membrane preparations from Torpedo californica.

Ion permeation, triggered by ligand-receptor interaction, is associated with the primary events of membrane depolarization at the neuromuscular junction and synaptic connections. To explore the possible sites of ion permeation, the long-lived fluorescent probe pyrene (fluorescence lifetime approximately 400 nsec) has been inserted into the lipid phase of acetylcholine receptor-rich membrane (AcChR-M) preparations from Torpedo californica. The pyrene probe is susceptible to both fluidity and permeability changes in the lipid bilayer. These changes are detected by variations in the rate of decay of the excited singlet state of pyrene after pulsation with a 10-nsec ruby laser flash. Variations of these lifetimes in the membrane preparations alone or in the presence of quenchers show that binding of cholinergic agonists and antagonists, neurotoxins, and local anesthetics to AcChR-M produces varying effects on the properties of the pyrene probe in the lipid phase. It is concluded that binding of cholinergic ligands to the receptor does not significantly alter the fluidity of permeability of the lipids in the bilayer contact with pyrene. On the other hand, local anesthetics do affect these properties.

Vapor-phase fluorescence spectra from the second excited singlet state of pyrene and its derivatives

Vapor-phase fluorescence spectra have been measured for pyrene and its simple derivatives, i.e., pyrene- d 10, 1-methylpyrene, and 4-methylpyrene. Each of these derivatives shows a weak fluorescence emission which is similar to the fluorescence from the second excited singlet state (S 2) of pyrene and is to be assigned to the S 2-fluorescence. The methyl substitution causes frequency shifts (Δ ν) in both absorption and fluorescence, and the Δ ν values for absorption and fluorescence transitions that are associated with the same excited state, i.e., the first excited singlet state (S 1) or the second excited singlet state (S 2), are approximately equal to each other. When the excitation energy increases, the S 2-fluorescence shifts gradually to the red in almost the same way as the S 1-fluorescence. The S 2-fluorescence spectrum has a sort of mirror-image relation to the S 2-absorption. A comparison of S 2-emissions of pyrene and pyrene- d 10 suggests that the ratio between the quantum yields of S 2- and S 1-fluorescence may be related to a ratio ϱ 2 ϱ 1 , where ϱ 1 and ϱ 2 are the densities of vibrational states in S 1 and S 2 at the energy of excitation.

The absorption spectrum of the first excited singlet state of pyrene obtained by modulation excitation spectrophotometry

The absorption spectrum of the first excited singlet state of pyrene dissolved in polymethylmethacrylate has been obtained over the range 390–500 nm using modulation excitation spectrophotometry. The advantages of this technique as compared to nanosecond laser flash photolysis are discussed.

Singlet excited monomer and excimer absorptions of pyrene

The absorption and polarization spectra from the first excited singlet state of pyrene and the absorption spectrum of the pyrene excimer are presented. These results were obtained by laser flash spectroscopy using a frequency doubled ruby laser pulse of 6 nanoseconds halfwidth. A qualitative preliminary assignment of the bands is given.

Fluorescence from the second excited singlets of pyrene and 3,4-benzpyrene

The fluorescence from the second excited singlet state of pyrene and 3,4-benzpyrene in the vapour phase has been observed. The effect of inert gas, temperature and excitation frequency has been investigated. The estimated rate constants for the internal conversion and the reverse process for pyrene are 2 × 10 12 s −1 and 10 7 s −1 respectively.