Pyrene Excimer Emission Research Articles

Ultrafast Dynamics of Pyrene Excimer Formation in Y Zeolites

Pyrene excimer emission in alkali-metal-exchanged zeolites is readily observed to grow in using an ultrafast streak camera with 3.3 ps time-resolution. Rise-time constants range from 7 to 14 ps depending on the composition of the zeolite. These results show that two pyrene molecules in doubly occupied cavities must move from their pre-excitation orientation into the face-to-face orientation required for the excimer.

Ultrafast Dynamics of Pyrene Excimer Formation in Y Zeolites

Pyrene excimer emission in alkali-metal-exchanged zeolites is readily observed to grow in using an ultrafast streak camera with 3.3 ps time-resolution. Rise-time constants range from 7 to 14 ps depending on the composition of the zeolite. These results show that two pyrene molecules in doubly occupied cavities must move from their pre-excitation orientation into the face-to-face orientation required for the excimer.

Self-Association of Protected Newkome-Type Second-Generation Dendrimers at Nanomolar Level Concentrations in Aqueous Solution

Protected Newkome-type second-generation dendrimers (based on Lin's amine) were synthesized with a pyrene moiety attached to the core. The photophysical property in aqueous solution of the protected dendrimers shows self-association behavior in water. Pyrene excimer emission at 475 nm is observed in water even at very low concentrations of protected dendrimer (ca. 5 × 10-8 M). This emission band is absent in other solvents even up to a concentration of 10-5 M. The corresponding unprotected dendrimer does not show the pyrene excimer fluorescence. The amide of pyrene butyric acid with tert-butylamine shows the formation of excimer, albeit with very low intensity. Quenching studies on the dendrimer with hydrophilic quencher iodide anion (I-) reveal that there is significant quenching of fluorescence intensity in the case of N-tert-butyl-4-pyren-1-ylbutyramide as compared to that of the pyrene-attached second-generation protected dendrimer. This shows that the pyrene moiety in the case of the protected dendrimer is significantly shielded from the surrounding.

Synthesis of double-armed lariat ethers with pyrene moieties at each end of two sidearms and their fluorescence properties in the presence of alkali metal and alkaline earth metal cations.

Two types of double-armed lariat ether derivatives having pyrene moieties at each end of two sidearms, (3x + 1)-crown-x derivatives 1 (x = 5), 2 (x = 6), and 3 (x = 4) (type A) and 3y-crown-y derivatives, 6 (y = 5) and 7 (y = 6) (type B), were synthesized, and their complexation behavior toward alkali metal and alkaline earth metal cations was examined by fluorescence spectroscopy. Pyrene excimer emission decreased accompanied by an increase in monomer emission upon metal ion complexation. This finding is ascribed to the change of the spatial distance of two pyrene rings by movement suppression of both the crown ring and one of the two sidearms based on complexation with the metal cation. The selectivity for alkaline earth metal cations was highly dependent on the fitness of the host cavity and the guest size. Although most of the fluorophores did not respond to alkali metal cations, only trans-7a containing an 18-crown-6 ring showed K(+) selectivity.

Immobilization of pyrene on quartz plate surface via a flexible long spacer and its sensing properties to dicarboxylic acids

A novel photo-induced luminescence film has been prepared by immobilizing pyrene on quartz plate surface via a flexible long spacer, 1,3-diaminopropane and 3-glycidoxypropyl trimethoxysilane. The film shows combined monomer and excimer emission of pyrene in both wet and dry states. Steady-state and time-resolved fluorescence emission measurements demonstrated that the excimer emission mainly came from direct excitation of ground state dimers, and/or monomers in aggregated state. Classical Birks’ scheme plays little role in the formation of the excimers. The structures of the excimers formed during the excitation are complex. Both “standard excimer” of sandwich-like fully overlapped structure and ‘distorted excimer” of partially overlapped structure exist in the excited state of the fluorophore. The emission of the film is sensitive to the presence of dicarboxylic acids, including ethanedioic acid, malonic acid, succinic acid, etc. The emission in the monomer and excimer region increases along with increasing the concentration of the dicarboxylic acids. The time needed for the emission to reach equilibrium depends on the nature of the acids. It has been shown that the longer the chain length of the acids, the more the time needed. This observation is explained by considering the conformational reorganization of the immobilized pyrene due to insertion of the dicarboxylic acids into the space between neighboring spacers. Experimental results from similar studies using formic acid and acetic acid are in support of this explanation. Furthermore, the response of the film to dicarboxylic acids is reversible.

Monomolecular Layers of Pyrene as a Sensor to Dicarboxylic Acids

A novel photoinduced luminescence film has been prepared by immobilizing pyrene on a quartz plate surface via a flexible long spacer. The film shows combined monomer and excimer emission of pyrene both in wet and dry states, and the excimer may be formed mainly by direct excitation of ground-state dimers and/or monomers in aggregates. Classical Birks' scheme plays a little role in the formation of the excimers. The emission of the film is sensitive to the presence of dicarboxylic acids, including ethanedioic acid, malonic acid, succinic acid, etc. The emission in the monomer and excimer region increases with addition of the acids. The time needed for the emission to reach equilibrium depends on the nature of the acids. It has been shown that the longer the chains of the acids, the more time is needed. This observation is explained by considering the conformational reorganization of the immobilized pyrene due to insertion of the dicarboxylic acids into the space between neighboring spacers. Experimental re...

Solution Properties of Hydrophobically-Modified Phosphorylcholine-Based Polymers in Water and in the Presence of Surfactants

The photophysical properties of a fluorescently labeled amphiphilic polybetaine have been investigated by steady state and time-resolved fluorescence spectroscopy. The copolymer consists of N-isopropylacrylamide and N-phosphorylcholine-N‘-ethylenedioxybis(ethyl)acrylamide units in ∼1/1 molar ratio, as well as 5 mol % of N-[(1-pyrenyl)-4-butyl]-N-n-(octadecyl)acrylamide. In water, individual copolymer chains associate in multichain aggregates held together by hydrophobic interactions between the hydrocarbon chains and by ion pair formation between the phosphorylcholine groups. By monitoring the changes in the ratio of the pyrene excimer emission intensity (IE) to the pyrene monomer emission intensity (IM), we established (1) that the polymer assemblies are disrupted by the addition of divalent salts, such as CaCl2 and (2) that interactions take place between the polymer and anionic, cationic, zwitterionic, or neutral surfactants. The mechanism of binding is discussed in terms of surfactant charge and chain...

Aggregation behavior of hydrophobically modified dextran in aqueous solution: a fluorescence probe study

Dextrans ( M W=11.000 and M w=40.000) have been modified with 4-hexyl benzoyl chloride and their aggregation behavior was studied in aqueous solution employing the fluorescent probes pyrene and 1,8 anilinonaphtalene sulfonic acid sodium salt (1,8 ANS). The photophysical studies showed that above a critical concentration the derivatives tend to form aggregates having different properties, which depend on both the degree of substitution ( α) and the molecular weight of the sample. The parameter α has a marked effect on the critical aggregation concentrations (CAC) and aggregate properties. Hydrophobic microenvironments can be detected for substituted dextrans having α values varying from 0.01 to 0.19. CAC values decreased by two orders and magnitude when the molecular weight increased from 11 to 40 kDa, leading to formation of more apolar aggregates and diminishing by about 30% the polarity of the microenvironments. Pre-aggregation was evidenced by pyrene excimer emission and intermolecular interactions were responsible by the formation of aggregates leading to solution behaviour similar to that of common surfactants.

Reversible regulation of pyrene excimer emission by light and metal ions in the presence of photochromic spiropyran: toward creation of a new molecular logic circuit.

The excimer fluorescence of a bis-pyrene molecule can be reversibly regulated by ultraviolet light, metal ions and visible light in the presence of spiropyran. Based on this result, a new molecular logic circuit is proposed.

A Ratiometric Fluorescent Sensor for AgI with High Selectivity and Sensitivity

A bicyclic cycloadduct 1 bearing a pyrenyl moiety has been synthesized and investigated as a ratiometric fluorescent sensor for AgI. In an aqueous ethanol solution of 1, the presence of silver ion induces the formation of a 1:2 metal-ligand complex, which exhibits a strong intensity enhancement of the pyrene excimer emission at the expense of the emission of monomeric pyrene.

Self-association of hyperbranched poly(sulfone-amine) in water: studies with pyrene-fluorescence probe and fluorescence label

Both pyrene-fluorescence probe and fluorescence label techniques are used to investigate the association behaviors of hyperbranched poly(sulfone-amine) (HPSA) in aqueous solution. In the presence of HPSA, excimer emission peak evidently appeared, while no excimer peak was observed in the emission spectra in the absence of HPSA. The excitation spectrum monitored at excimer emission red shifts by about 38–40nm compared to that monitored at monomer emission, which shows that the excimer is formed by preassociated pyrene chromophores. In the same concentration of pyrene, monomer emission of pyrene decreases but excimer emission increases with increasing the concentration of HPSA; the ratio of excimer-to-monomer emission intensity (IE/IM) gradually increases, reaches a critical point at 5–7g/l, and sharply increases with the concentration. Pyrene-labeled hyperbranched poly(sulfone-amine) (Py-HPSA) was synthesized from 4-(1-Pyrene)butyroyl chloride and HPSA. The monomer emission and excimer emission of Py-HPSA show the concentration-quenching effect, while IE/IM increases monotonously, approaches a critical point, and then suddenly increases with increasing the concentration of Py-HPSA. Influences of acidity and solvents on the fluorescence emission were studied. In high concentrations of hyperbranched polymer, pH and DMSO significantly influence the emission of pyrene, and excimer peak disappears at 72% of DMSO fraction.

Interesting fluorescence properties of C60-centered dendritic adduct with twelve symmetrically attached pyrenes.

A C60-centered dendritic adduct with 12 symmetrically attached pyrene species was synthesized and found to have relatively simple fluorescence emission kinetics, in particular, the mono-exponential decay of the significant pyrene excimer emission.

Interactions of functionalized carbon nanotubes with tethered pyrenes in solution

Single-wall carbon nanotubes (SWNTs) were functionalized by oligomeric species containing derivatized pyrenes. Absorption and emission properties of the pyrene moieties tethered to the functionalized SWNTs were studied in homogeneous solution. The absorption spectra suggest no significant ground-state complexation between the pyrenes and nanotubes. The fluorescence and fluorescence excitation results show that the tethered pyrenes form “intramolecular” (intra-nanotube) excimers and that the excimer formation is predominantly dynamic in nature. The time-resolved fluorescence results show that the pyrene monomer and excimer emissions are significantly quenched by the attached SWNTs. The quenching is explained in terms of a mechanism in which carbon nanotubes serve as acceptors for excited-state energy transfers from the tethered pyrene moieties.

Fluorometric sensing of alkaline Earth metal cations by new lariat ethers having plural pyrenylmethyl groups on the electron-donating sidearms.

[structure: see text] New fluorescent compounds (1), lariat ethers having plural pyrenylmethyl groups on the sidearms, were prepared, and their complexation behavior with alkaline earth metal cations was examined by fluorescence spectrometry. The pyrene excimer emission decreased accompanied with an increase in the monomer emission upon complexation with the metal ion. This finding is ascribed to the cooperative participation of one of the two sidearms in the complexation of the crown ring with the metal ion.

Crown Ether Functionalized Lipid Membranes: Lead Ion Recognition and Molecular Reorganization

A fluorescent lipid bilayer, functionalized with 18-crown-6, was developed to examine the mechanism of chemical recognition-induced molecular reorganization events in a membrane system. The synthetic receptor-lipid, PS18C6, was prepared with the crown ether at the headgroup position and a pyrene fluorescent tag on the hydrophobic tail. When incorporated into bilayers of distearylphosphatidylcholine, the receptor-lipid aggregated into domains, evidenced by the relatively large pyrene excimer emission from the bilayer. Langmuir pressure−area (π−A) isotherm measurements and atomic force microscopy (AFM) further aided in characterizing the receptor aggregation at the macro- and nanoscale, respectively. The functionalized bilayer exhibited selective affinity for mercuric and lead ions in aqueous buffered solution (pH 7.4), with a fluorescence response that was linear over the concentration range 10-7 to 10-4 M metal ions. 1H NMR studies established that the binding stoichiometry of PS18C6 with lead was 1:1, with Ka = 105 M-1 in methanol. Recognition and binding of lead ions at the membrane surface resulted in a rapid and prominent reorganization of the receptor-lipids in the membrane that was measurable at both the macro- and nanoscales. Removal of the lead ions, through the addition of EDTA, resulted in recovery of the original fluorescence and the reaggregation of structures in the membrane.

Fluorescence studies of pyrene maleimide-labeled translin: excimer fluorescence indicates subunits associate in a tail-to-tail configuration to form octamer.

Translin is an octameric single-stranded DNA binding protein consisting of 228 amino acid residues per monomer. This protein contains two cysteine residues per monomer. Studies of reactions with DTNB show that both cysteines are reactive and exhibit biphasic reaction kinetics. Further studies with two site-directed mutants, C58S and C225S, confirm that Cys-58 reacts slowly while Cys-225 reacts quickly. Pyrene excimer emission was observed for pyrene maleimide-labeled C58S mutant. This was not observed, however, with the pyrene maleimide-labeled C225S mutant. DAS (decay associated spectra) revealed that all excited pyrene labels on C225 residues can form excimers with pyrenes of adjacent subunits within a few nanoseconds. Time-resolved emission anisotropy detects a rotational correlation time appropriate for octameric but not dimeric species. These results indicate proximity for the Cys-225 residues on adjacent monomers and that the subunits must interact in a tail-to-tail orientation. Moreover, disulfide bonds are not required for the formation of an octamer.

Segmental Mobility in Phosphorus-Containing Dendrimers. Studies by Fluorescent Spectroscopy

Steady-state fluorescence spectra and decays of excitations of a phosphorus-containing dendrimer labeled with 12 internal labels and of an iminophosphorane model compound bearing two labels dissolved in acetonitrile, diglyme, 1,4-dioxane, triethylene glycol, and cyclohexanol revealed that the interior of dendrimers contained many solvent molecules, and movements of internally located pyrene labels were not reduced by interactions with the dendrimer core. This conclusion was based on the following findings. A ratio of the intensities of pyrene−pyrene excimer and pyrene monomer emissions (IE/IM) decreased with increasing solvent viscosity but, with exception of acetonitrile solutions, was very close for the dendrimers and for the model. Monomer and excimer emission intensity decays were fitted with two-exponential functions with time constants τ1 and τ2 characterizing formation of pyrene−pyrene excimers and recovery of pyrene moieties in their ground state, respectively. For solvent viscosities varying from...

An assessment by fluorescence spectroscopy of the stability of polyanions/positively charged liposome systems in the presence of polycations

The interactions between cationic non-phospholipid liposomes and pyrene-labeled hydrophobically modified sodium poly-2-(acrylamido)-2-methylpropane sulfonates (HM-PAMPS) have been examined by fluorescence spectroscopy and dynamic light scattering. Evidence from changes in the relative intensity of pyrene excimer and monomer emissions indicates that the polyanions bind to cationic liposomes and that, for systems in aqueous 0.2M NaCl, the binding is only mildly affected by the charge density of the liposomes. The reversibility of the polyanion binding to the liposomes was assessed by addition of the polycation (N-isopropylacrylamide)–N-dimethylethyl(2-acrylamidoethyl)ammonium bromide copolymer (PNIPAM–DMEAB). Based on the level of pyrene fluorescence recovery upon addition of the polycation to complexes between PAMPS and liposomes containing a quencher of fluorescence in their bilayer, we demonstrate reversibility of the binding of sodium poly-2-[acrylamido-2-methylsulfonate–N-(1-pyrenylmethyl)]acrylamide (PAMPS–Py1). In contrast, under the same conditions, a HM-PAMPS sample carrying along its backbone 5mol% of n-octadecyl groups is not desorbed from the surface of the liposome.

Cu2+-induced blue shift of the pyrene excimer emission: a new signal transduction mode of pyrene probes.

A pentiptycene-bispyrenyl system (1) has been synthesized and investigated as a fluorescent chemosensor for metal ions. A novel blue shift along with an intensity enhancement of the pyrene excimer emission is observed for 1 in the presence of Cu(2+). Such a new signal transduction mode of pyrene probes results from the formation of a static pyrene excimer that has very different characteristics from its dynamic counterpart.

Molecular Dynamics of Monopyrenyl Lipids in Liposomes from Global Analysis of Time-Resolved Fluorescence of Pyrene Monomer and Excimer Emission

The diffusion coefficients of 1-palmitoyl-2-(pyrenodecanoyl)-sn-glycero-3-phosphocholine (pyr10PC) in different bilayer membranes are determined from global analysis of the time-resolved fluorescence of the pyrene monomer and excimer emissions. The global kinetic model involves a time-dependent reaction rate coefficient derived from the analytical solution of the diffusion equation for bimolecular reactions in the two-dimensional surface of the membrane. The bilayer membranes are single unilamellar vesicles (SUV's or liposomes) composed of dioleoylphosphatidylcholine (DOPC), 1-stearoyl-2-arachidonoylphosphatidylcholine (SAPC), or dipalmitoylphosphatidylcholine (DPPC). All SUV's except the one composed of DPPC are in the liquid crystalline state. Liposomes composed of mixtures of DOPC and SAPC in various molar ratios are also investigated by the pyrene excimer reaction. The diffusion constant becomes larger when the fraction of SAPC in the mixed bilayers increases, indicating an apparent increase in fluidity. The latter observation is supported by photostationary measurements of the pyrene excimer to monomer intensity ratios of the same liposomes.