Excimer Emission Intensity Research Articles

DNA detection via programmed core-shell nanodot-assembly with concomitant fluorescence modulation

In this work, we designed and demonstrated a new DNA probe working on the principle of the fluorescence change with improved detection capability via building a cruciform DNA hybrid with target ODNs. In our oligodeoxynucleotide-pyrene-oligodeoxynucleotide (OPO) probe, hybridisations between the probes (OPO) and target oligodeoxynucleotides (ODNs) are programmed to induce the formation of core-shell (pyrene-ODN) nanodot structure in aqueous solution to generate and maintain their excimer emission more efficiently. Since this novel OPO probe showed wide detection range, high-excimer emission efficiency and high reliability of excimer emission intensity, the probe is capable of application to diagnosis of genetic disease and detection of increased DNA copy number and occurrence of mutation in a real-time PCR.

Effects of Metal Cation Coordination on Fluorescence Properties of a Diethylenetriamine Bearing Two End Pyrene Fragments

Fluorescence properties of a diethylenetriamine bearing two end pyrene fragments (L) have been studied in water, where effects of adding metal cations (Zn2+, Cd2+, Cu2+, Hg2+, Ag+) on the emission properties of L have been studied. Without metal cations, L shows dual-mode fluorescence consisting of monomer and excimer emissions. The monomer emission intensity (I(M)) is strong at acidic pH but decreases with a pH increase because of an electron transfer (ET) from the unprotonated nitrogen atoms to the excited pyrene fragment. The excimer emission is due to the static excimer formed via a direct photoexcitation of the intramolecular ground-state dimer (GSD) of the end pyrene fragments. The excimer emission intensity (I(E)) is weak at acidic pH but increases with a pH increase because of the GSD stability increase associated with the deprotonation of the polyamine chain. Addition of metal cations leads to I(M) decrease, where chelation-driven I(M) enhancement does not occur even with diamagnetic Zn2+ and Cd2+ at any pH. This is because a pyrene-metal cation pi-complex, formed via a donation of pi-electron of the pyrene fragment to the adjacent metal center, suppresses the monomer photoexcitation. I(E) also decreases upon addition of metal cations because the pyrene-metal cation pi-complex weakens pi-stacking interaction of the end pyrene fragments, leading to GSD stability decrease. The emission properties of L-Zn2+ complexes were studied by means of time-resolved fluorescence decay measurements, and the effects of adding a less-polar organic solvent were also studied to clarify the detailed emission properties.

Solvent-Driven Multiply Configurable On/Off Fluorescent Indicator of the pH Window: A Diethylenetriamine Bearing Two End Pyrene Fragments

Fluorescence behaviors of a simple-structured molecule (L), a diethylenetriamine bearing two end pyrene fragments, have been investigated in water. Effects of adding a less-polar organic solvent (acetonitrile: MeCN) on the emission behaviors have been studied by means of steady-state and time-resolved fluorescence measurements. L dissolved in water shows dual-mode fluorescence consisting of monomer and excimer emissions. The monomer emission shows an "on-off" intensity profile against the pH window (pH 2-12), whereas the excimer emission shows an "off-on" profile. Upon MeCN addition, the monomer emission maintains the "on-off" profile. In contrast, the "off-on" profile of the excimer emission is drastically changed: L shows two more types of profiles, "off-on-off-on" and "off-on-off", along with the MeCN concentration increase, thus behaving as a multiply configurable fluorescent indicator of the pH window. The MeCN-driven excimer emission switching of L is triggered by (i) the decrease in stability of the intramolecular ground-state dimer (GSD) formed between the end pyrene fragments, which suppresses the direct photoexcitation of GSD (suppression of the "static" excimer formation), leading to a decrease in the excimer emission intensity at basic pH; and (ii) the decrease in polarity of solution, which allows formation of a "dynamic" excimer via a monomer-to-excimer transition, resulting in an enhancement of the excimer emission intensity at acidic-neutral pH.

Luminescence of Ruthenium Halide Complexes Containing a Hemilabile Phosphine Pyrenyl Ether Ligand

A series of Ru(II) complexes, tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3), Br (4), I (5)), containing the hemilabile phosphine pyrenyl ether ligand 4-{2-(diphenylphosphino)phenoxy}butylpyrene (POC4Pyr (1)) are reported. The synthesis and spectroscopic properties of both the ligand, POC4pyr (1), and ligand oxide, P(=O)OC4pyr 2, and the solid-state structure of 1 are reported. Complexes 3-5 react rapidly with CO to give complexes ttt-RuX2(CO)2(POC4pyr-P)2 (X = Cl (6), Br (7), I (8)). No pyrene excimer emission is detected from 3-5; however, different intensities of excimer emission are observed for 6-8. The intensity of excimer emission decreases through the series, with 6 showing the most intense response. The emission is solely due to intramolecular pyrene excimers at low concentrations (< or =10(-4) M). Comparison of the UV-vis and steady-state fluorescence spectra shows overlap between the low energy d-d absorption of 7 and 8 with excimer emission (480 nm), suggesting nonradiative energy transfer may be occurring. Once excess CO is removed, complexes 6-8 isomerize to cis-dicarbonyl complexes cct-RuX2(CO)2(POC4Pyr-P)2 (X = Cl (9), Br (10), I (11)). The intensity of excimer emission from 9-11 increases with respect to the excimer emission observed for 6-8, with 9 showing a significant increase in excimer intensity.

A Pyrene‐Labeled G‐Quadruplex Oligonucleotide as a Fluorescent Probe for Potassium Ion Detection in Biological Applications

Ion probes: A potassium-sensing oligonucleotide with terminal pyrene moieties can be used as a fluorescent probe for the real-time monitoring of the extracellular concentration of K+ ions under physiological conditions. The excimer emission intensity (b) of the chair-type quadruplex structure formed depends on the K+ ion concentration (0–200 mm), and differs significantly from that in the absence of potassium (a). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2005/z501506_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Unique molecular recognition property of bis-pyrene-modified β-cyclodextrin dimer in collaboration with γ-cyclodextrin

β-Cyclodextrin (β-CyD) dimer modified with two pyrene moieties, 6-(2-pyrenebutylate-aminoethyl)pyrenebutylate-amino-6-deoxy-bis-β-CyD (β-1) has been prepared to investigate the chemo-sensing ability for organic guests and the host–guest complexation behavior in the presence of γ-CyD. This fluorescent cyclodextrin dimer showed monomer and excimer emissions; the guest-induced emissions were observed as increase or decrease depending on the guest molecules. The sensing parameters, Δ I m / I m 0 and Δ I ex / I ex 0 , were used to describe the sensing ability of β-1, where I m 0 , I m, I ex and I ex 0 were fluorescence intensities of monomer and excimer emission, respectively, in the presence and absence of the guest and Δ I m = I m − I m 0 and Δ I ex = I ex − I ex 0 . This host particulary able to distinguish between ursodeoxycholic acid and chenodeoxycholic acid, which are related as diasteromer. It is observed that supramolecular association between the β-1 and γ-CyD was formed in the presence of 1-adamantanol and bisphenol A as a guest. In this work, we succeeded to make a new type of supramolecular assembly system based on hetero association between a guest, β-1 and γ-CyD.

Fluorescence observations on complex formation between linear and hyperbranched polyelectrolytes in dilute aqueous solutions

The complexation between poly(ethylene imine) (PEI) and poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) or AMPS copolymers was investigated with the relative excimer emission intensity I E/ I M of a cationic probe 1-pyrenemethylamine hydrochloride (PyMeA · HCl), fluorescence nonradiative energy transfer (NRET) I Py/ I Np of naphthalene to pyrene labels, the fluorescence anisotropy r and I E/ I M of pyrene labels. PEI was a hyperbranched weak polycation in acid solution, which formed complex with anionic polyelectrolytes due to the electrostatic attraction. The I E/ I M of PyMeA · HCl probe decreased to zero, the intra-, intermolecular NRET I Py/ I Np and I E/ I M of pyrene labels on the AMPS copolymers reached their maxima when χ was increased from 0 to 2.4, which was defined as the mole ratio of the amino group in PEI to the AMPS group in the polyanion. These facts indicated the formation of nonstoichiometric complex of the oppositely charged polyelectrolytes when χ = 2.4 at the concentration much lower than their overlap concentrations. The intermolecular aggregate appeared as indicated by an increase in the intermolecular I Py/ I Np and r with χ up to 2.4 due to neutralizing and hydrophobizing the polyelectrolytes and the bridging effect of the PEI chain bound on different polyanion chains. At high pH, PEI became a neutral polymer and did not bind with the AMPS anion to form the complex as illustrated by the constant value of r for the pyrene labels attached to the AMPS polyanion as that without addition of PEI. The amino group in PEI quenched pyrene and naphthalene emission, resulting a decrease in both I Np and I Py.

Study of the diffusion of pyrene in silicone polymer coatings by steady state fluorescence technique: effects of pyrene concentration

The concentration dependence of the diffusion coefficient of pyrene in single component and two-component room temperature curing silicone polymer coatings is investigated by the steady state fluorescence technique by measuring the pyrene excimer fluorescence intensity. At pyrene concentrations lower than 10 mM, the intensity of excimer fluorescence is proportional to the concentration and at higher concentrations it deviates from this trend due to concentration quenching. Thermal aging studies show that this concentration quenching can be removed by thermal annealing and the excimer emission intensity approaches the value expected from the trend at lower concentrations. The diffusion coefficient of pyrene at low concentrations in silicone polymer coatings is obtained using the approximate solution of one-dimensional diffusion equation. A modified approach is employed to estimate the diffusion coefficient at higher pyrene concentrations. In this method, the excimer intensity and time scale are shifted, respectively to I max the maximum value of excimer intensity attained during annealing and t max, the time taken to reach this. The estimated diffusion coefficients at different pyrene concentrations show a negligible dependence on pyrene concentration in both types of polymers. These results are attributed to the high structural mobility of silicone polymer chains due to their molecular structure.

Excimer emission from cathode boundary layer discharges

The excimer emission from direct current glow discharges between a planar cathode and a ring-shaped anode of 0.75 and 1.5 mm diameter, respectively, separated by a gap of 250 μm, was studied in xenon and argon in a pressure range from 75 to 760 Torr. The thickness of the “cathode boundary layer” plasma, in the 100 μm range, and a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the cathode fall and the negative glow. The radiant excimer emittance at 172 nm increases with pressure and reaches a value of 4 W/cm2 for atmospheric pressure operation in xenon. The maximum internal efficiency, however, decreases with pressure having highest values of 5% for 75 Torr operation. When the discharge current is reduced below a critical value, the discharge in xenon changes from an abnormal glow into a mode showing self-organization of the plasma. Also, the excimer spectrum changes from one with about equal contributions from the first and second continuum to one that is dominated by the second continuum emission. The xenon excimer emission intensity peaks at this discharge mode transition. In the case of argon, self-organization of the plasma was not seen, but the emission of the excimer radiation (128 nm) again shows a maximum at the transition from abnormal to normal glow. As was observed with xenon, the radiant emittance of argon increases with pressure, and the efficiency decreases. The maximum radiant emittance is 1.6 W/cm2 for argon at 600 Torr. The maximum internal efficiency is 2.5% at 200 Torr. The positive slope of the current–voltage characteristics at maximum excimer emission in both cases indicates the possibility of generating intense, large area, flat excimer lamps.

Enhancement of color purity in blue-emitting fluorene–pyridine-based copolymers by controlling the chain rigidity and effective conjugation length

A series of high molecular weight, readily soluble copolymers of 9,9-dioctylfluorene with pyridine (less than or equal to 50 mol%) are synthesized by Suzuki polycondensation. Copolymers emit blue light and exhibit high PL efficiency. PL efficiencies show the maximum at 3,5-pyridine content of around 30 mol% in the copolymer. With further the increase of meta-linkage contents, PL efficiencies decrease rapidly to15% for alternating copolymer. Cyclic voltammetry investigation reveals that LUMO levels of copolymers increase with the increase of pyridine content. The introduction of pyridine unit at 3,5-position into polyfluorene backbone significantly depresses the excimer formation. The intensity of excimer emission decreases with the increase of 3,5-pyridine contents. Narrow and pure blue EL emission is obtained for copolymer with pyridine content of 40 mol%. External quantum efficiency is moderately high (0.4–0.5%) for such a pure blue emitter. The threshold voltages of devices from copolymers with the pyridine content of less than 40 mol% are low in the range of 5–6 V based on the device configuration: ITO/PEDOT/polymer/Ba/Al. The results indicate that fluorene- co-3,5-pyridine copolymers are promising blue-emitting electroluminescent materials.

Investigations of the effect of viscosity of resin on the diffusion of pyrene in silicone polymer coatings using steady state fluorescence technique

The diffusion phenomenon of pyrene in silicone coatings prepared from various commercial silicone resins with different viscosities was investigated using steady state excimer fluorescence technique. The amount of pyrene lost from the coatings by diffusion at different temperatures ranging from 25 to 70 °C was estimated from the excimer emission intensity. The diffusion coefficients ( D) and activation energy of diffusion of pyrene in silicone coatings were determined. It was found that the kinetic parameters of pyrene were comparable in all the four silicone coatings and independent of the viscosity of the resin. The D values were lower than those expected for pyrene in PDMS resins in the corresponding viscosity range. This may be attributed to restricted mobility of pyrene due to cross-linking of polymer chains in the cured silicone coatings.

Argon excimer emission from high-pressure microdischarges in metal capillaries

We report on argon excimer emission from high-pressure microdischarges formed inside metal capillaries with or without gas flow. Excimer emission intensity from a single tube increases linearly with gas pressure between 400 and 1000 Torr. Higher discharge current also results in initial intensity gains until gas heating causes saturation or intensity drop. Argon flow through the discharge intensifies emission perhaps by gas cooling. Emission intensity was found to be additive in prealigned dual microdischarges, suggesting that an array of microdischarges could produce a high-intensity excimer source.

Excimer emission from microhollow cathode argon discharges

Microhollow cathode discharges (MHCDs) operated in rare gases are sources of intense excimer emission. Of particular interest is argon, because of its relatively low cost and the short wavelength (128 nm) of its excimer emission. The measured internal efficiency, obtained in static argon at atmospheric pressure, was found to be on the order of 1%. Flowing argon through a direct current (DC) MHCD at atmospheric pressure caused the argon excimer internal efficiency to increase to 6%, indicating that the low efficiency in static argon is mainly due to impurities. Applying 10 ns pulses to the DC plasma resulted in an increase in excimer power from 30 mW DC to 180 mW peak power, at an efficiency of 5–6%. The increase in excimer power correlates with an increase in the electron density. For DC operation, electron densities of 1015 cm−3 were measured in atmospheric pressure argon micro-plasmas, which increased to values beyond 1016 cm−3 for nanosecond pulsed operation. This increase in electron density and excimer power is due to pulsed electron heating, an effect that has allowed us to raise the mean electron energy from 1 eV, for DC operation, to 2.25 eV in the pulsed mode.

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...

Steady-State Fluorescence of Dye-Sensitized TiO2 Xerogels and Aerogels as a Probe for Local Chromophore Aggregation

Sol-gel synthesis has been used to disperse an emissive chromophore within a porous TiO 2 matrix, leading to xerogels and aerogels doped with tethered and unbound pyrenyl groups. Steady-state fluorescence was used to probe the interactions of neighboring pyrene groups within the gel matrix. Changes in the relative intensity of the monomer (I 1 ) emission peak as a function of chromophore concentration indicated a local interaction between included dyes for both tethered and unbound pyrene groups, likely through π stacking. Partial matrix methylation or phenylation failed to produce a significant effect on the relative intensity of the I 1 signal in either the xerogel or the aerogel. Changes in the relative intensity of excimer emission with changes in matrix composition, however, do suggest that the presence of either phenyl or methyl groups within the TiO 2 matrix impedes π stacking between pairs of tethered pyrenyl groups. Compared with strong excimer emission in the xerogels containing pyrenyl groups at relatively high concentrations, excimer formation was inhibited in the corresponding aerogels, for which BET analysis indicated a broad pore size distribution in the mesoporous range, ca. 100 A.

Excimer Formation in a Naphthalene-Labeled Dendrimer

Steady-state and time-resolved fluorescence measurements were conducted on newly synthesized Frechet-type dendrimers with naphthalene peripheral groups in homogeneous and sodium dodecyl sulfate (SDS) micellar solutions. Intense excimer emission was observed for the third-generation dendrimer 3 but not for the first-generation dendrimer 1a. This different spectroscopic behavior was attributed to the geometry of dendrimer 3, where excimeric interactions between adjacent π-stacked naphthyl groups are present.

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...

Fluorescence Properties, Induced-Fit Guest Binding and Molecular Recognition Abilities of Modified γ-Cyclodextrins Bearing Two Pyrene Moieties

Abstract γ-Cyclodextrin (γ-CD) derivatives bearing two pyrene moieties at AB, AC, AD, and AE glucose units (1–4), were prepared as chemosensors for detecting molecules by their guest-responsive excimer emission intensity. All these hosts exhibited predominant excimer emission and remarkable induced circular dichroism (ICD) in a 20% dimethyl sulfoxide aqueous solution. The excimer emission and the ICD intensities mostly decreased upon addition of a variety of organic guests. The result indicates that 1–4 undergo an induced fit conformational change upon complex formation, excluding the pyrene moieties from inside to outside the γ-CD cavity in guest binding. The guest-induced fluorescence variations were analyzed by 1 : 1 host–guest stoichiometry and the obtained binding constants were roughly correlated with the guest-induced fluorescence variations. The binding and fluorescence data revealed that 1–4 have remarkable molecular recognition abilities for bile acids and other guests.

Association of α-helix peptides that have γ-cyclodextrin and pyrene units in their side chain, and induction of dissociation of the association dimer by external stimulant molecules

α-Helix peptides bearing one unit of γ-cyclodextrin (γ-CD) and one or two units of pyrene in their side chain have been designed and synthesized as a novel system of peptide dimerization. The dimer was formed based on inclusion of two pyrene units in the γ-cyclodextrin cavity, and the dissociation of the peptide dimer was induced by external stimulant molecules (guests). Circular dichroism studies showed that the cyclodextrin–peptide hybrids (CD–peptides) maintain relatively rich α-helix content (61 to 81%), which was not affected by the guest inclusion into the cyclodextrin cavity. Fluorescence studies revealed that these CD–peptides form stable association dimers, which exhibit excimer emission. The intensity of the pyrene excimer emission decreased upon addition of the guest molecules, indicating dissociation of the CD–peptide dimers to the monomer CD–peptides. These CD–peptide hybrids bind structurally similar steroidal compounds with remarkable discrimination. These results demonstrate that this molecule-assembly system, based on host–guest chemistry, could be applicable to the development of molecule-responsive materials or a molecule-sensing system.

Photodegradation of Pyrene-Labeled Polystyrene Adsorbed on Silica Surface in Chloroform

Photodegradation of Pyrene-Labeled Polystyrene Adsorbed on Silica Surface in Chloroform