Showing papers on "Excimer published in 2005"
TL;DR: Light-switching excimer aptamer probes for rapid and sensitive detection of a biomarker protein, platelet-derived growth factor (PDGF), were able to detect PDGF in a cell sample quantitatively without any sample pretreatment.
Abstract: Quantitative protein bioanalysis in complex biological fluids presents considerable challenges in biological studies and disease diagnosis. The major obstacles are the background signals from both the probe and the biological fluids where the proteins reside. We have molecularly engineered light-switching excimer aptamer probes for rapid and sensitive detection of a biomarker protein, platelet-derived growth factor (PDGF). Labeled with one pyrene at each end, the aptamer switches its fluorescence emission from ≈400 nm (pyrene monomer) to 485 nm (pyrene excimer) upon PDGF binding. This fluorescence wavelength change from monomer to excimer emission is a result of aptamer conformation rearrangement induced by target binding. The excimer probe is able to effectively detect picomolar PDGF in homogeneous solutions. Because the excimer has a much longer fluorescence lifetime (≈40 ns) than that of the background (≈5 ns), time-resolved measurements were used to eliminate the biological background. We thus were able to detect PDGF in a cell sample quantitatively without any sample pretreatment. This molecular engineering strategy can be used to develop other aptamer probes for protein monitoring. Combined with lifetime-based measurements and molecular engineering, light-switching excimer aptamer probes hold great potential in protein analysis for biomedical studies.
322 citations
TL;DR: Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized with enhanced fluorescence intensity and blue-shifted excimer emission.
310 citations
TL;DR: A new fluorescent sensor based on a pyrene/Zn(II)-dpa (dpa = bis(2-pyridylmethyl)amine) conjugate displays excimer emission selective for pyrophosphate over other anions.
157 citations
TL;DR: A new fluorogenic cone calix bearing two pyrene amide groups and its structural analogue 2 have been prepared and excited at 343 nm, 1 and 2 reveal excimer emissions at 448 and 472 nm, respectively.
Abstract: A new fluorogenic cone calix[4]triazacrown-5 (1) bearing two pyrene amide groups and its structural analogue 2 have been prepared. Excited at 343 nm, 1 and 2 reveal excimer emissions at 448 and 472 nm, respectively. When heavy metal ions such as Pb2+ and Co2+ are bound to 1, the fluorescence intensities of both monomer and excimer are quenched whereas H bonding-assisted F- binding to 1 gives rise to a quenched monomer emission with little excimer emission change.
151 citations
01 Jan 2005
TL;DR: In this paper, the authors present a review of the history of the development and development of Excimer Lasers and their applications in microlithography and micro-processing of Borosilicate Glass and Polymers.
Abstract: Introductory Remarks.- Fundamentals.- Some Fundamentals of Laser Physics.- Principles of Excimer Lasers.- Design and Technology of Excimer Lasers.- High-Repetition-Rate and High-Power Lasers.- High-Energy Lasers.- Excimer Lasers for Microlithography.- Laser Beam Characterization.- Optical Coatings for Excimer Laser Applications.- Small Structures with Large Excimer Lasers.- Historical Review of Excimer Laser Development.- Applications.- Overview.- Ablation.- Micro-Machining.- Via Drilling.- Micro-Processing of Borosilicate Glass and Polymers.- F2-Laser Microfabrication for Photonics and Biophotonics.- Nano-Structuring with Femtosecond Excimer Laser Pulses.- Physical Aspects of Ultra-Fast UV Laser Transfer.- Microlithography.- TFT Annealing.- Fiber Bragg Gratings.- Marking.- Activation and Metallization of Dielectrics.- Excimer-Laser Assisted Deposition of Carbon and Boron Nitride-Based High-Temperature Superconducting Films.- Combustion Analysis.- Medical Applications of Excimer Lasers.- High-Intensity Applications of Excimer Lasers.- High-Repetition-Rate Applications of Excimer Lasers.- New Frontiers: Extreme-Ultraviolet (EUV) Technology at 13.5 nm.- Trends in Worldwide Excimer Laser Sales.
122 citations
TL;DR: Peptide amphiphiles covalently functionalized with pyrene linked to the hydrophobic portion of the molecule exhibited excimer formation upon self-assembly into nanofibers, Interestingly excimer Formation was not observed in similar molecules that formed spherical aggregates rather than cylindrical nan ofibers.
Abstract: Certain peptide amphiphiles (PAs) in aqueous media are known to form high-aspect-ratio cylindrical nanofibers with hydrophobic cores. Using cholesterol or palmitic acid as the hydrophobe and the biological adhesion epitope RGDS as the hydrophilic segment, we studied the encapsulation of pyrene, a small hydrophobic molecule, within the cores of the self-assembling PA nanofibers. Circular dichroism (CD), transmission electron microscopy (TEM) and fluorescence were used to characterize formation of the supramolecular structures. Pyrene excimer formation observed by fluorescence demonstrated the encapsulation and aggregation of pyrene within the hydrophobic cores. In addition, peptide amphiphiles covalently functionalized with pyrene linked to the hydrophobic portion of the molecule exhibited excimer formation upon self-assembly into nanofibers. Interestingly excimer formation was not observed in similar molecules that formed spherical aggregates rather than cylindrical nanofibers.
110 citations
TL;DR: New fluorogenic or/and chromogenic calix[4]arenes 1-3 with two facing amide groups linked to fluorescent pyrene units are synthesized, showing a remarkably high selectivity for In(3+) over the other metal ions tested.
Abstract: New fluorogenic or/and chromogenic calix[4]arenes 1-3 with two facing amide groups linked to fluorescent pyrene units are synthesized. Orientations of the pyrene units are remote from each other in 1 and face-to-face pi-stacked in 2, which produces different photophysical properties. In the excited state, the two pyrene units of 2 form a strong intramolecular excimer displaying an emission at 472 nm with a relatively weak monomer emission at 395 nm. In contrast, 1 exhibits only a monomer emission at 398 nm because intramolecular hydrogen bonding between the phenolic OH oxygens and the amide hydrogens prevents pi-stacking of the two pyrene groups. Fluorescence changes upon addition of various metal ions show that 1 has a remarkably high selectivity for In(3+) over the other metal ions tested. Compound 1 forms 2:1 (metal:ligand), as well as 1:1 complexes, with In(3+), with fluorescence varying uniquely with the complex stoichiometry. Compound 3, which possess two pyrene units and two chromogenic azo groups, shows almost the same binding behavior toward metal ions as does 1, together with additional bathochromic shifts of the absorption maximum. Compared with 1, compound 3 emits a considerably weaker fluorescence, which is attributed to electron transfer from the pyrene units to the nitro groups of the phenylazo moieties.
99 citations
TL;DR: It was found that changing the concentration ratio of the pyrene to SDS molecules could be employed to control the aspect ratio and the characteristic fluorescence of the isolated pyrene molecules was suppressed and concurrently replaced by the excimer emission of the Pyrene nanostructures.
Abstract: Morphology-controllable synthesis of various pyrene nanostructures from nanoparticles to short nanorods and nanowires (long nanorods) was achieved by a simple self-assembly method. In this approach, aqueous sodium dodecyl sulfate (SDS) micelles were used as templates to direct the self-assembly of the pyrene molecules into nanorods. It was found that changing the concentration ratio of the pyrene to SDS molecules could be employed to control the aspect ratio (length to diameter) of the pyrene nanostructures from 1 to 50 or higher. Moreover, the dimensional variation was accompanied by changes of their optical properties. With the increase of the aspect ratio, the characteristic fluorescence of the isolated pyrene molecules was suppressed and concurrently replaced by the excimer emission of the pyrene nanostructures. A blue-shift was observed in the excimer emission peaks as the length of the nanorods increased. The growth mechanism and the change in optical properties of these pyrene nanostructures were d...
97 citations
TL;DR: Quenching of the monomer and excimer emissions from pyrene allows excellent discrimination in the detection of electron-deficient molecules; this characteristic could be used to detect explosives and for rapid screening of complex samples suspected of containing explosives.
Abstract: Quenching of the monomer and excimer emissions from pyrene allows excellent discrimination in the detection of electron-deficient molecules; this characteristic could be used to detect explosives and for rapid screening of complex samples suspected of containing explosives. The method responds to electron deficient molecules other than nitro compounds (e.g., 1,4-dicyanobenzene), giving some false positives; in this case, however, the method is unlikely to lead to false negatives, a desirable characteristic in security-related applications.
83 citations
TL;DR: F fluorogenic calix[4]arenes (1 and 2) bearing a pendent ethyleneamine on their triazacrown rings, respectively, were synthesized in the cone conformation, showing a high selectivity for F- ions over other anions tested and a relatively weak emission.
Abstract: Fluorogenic calix[4]arenes (1 and 2) bearing a pendent ethyleneamine on their triazacrown rings, respectively, were synthesized in the cone conformation. Compared with 4, free 1 and 2 display a relatively weak emission, reflecting that a PET process from the pendent amine group (−CH2CH2NH2) to the fluorogenic pyrenes is mainly operated. Addition of various metal ions or anions to the solution of 1 or 2 reduces the PET because the pendent alkylamine takes part in the complexation, causing their fluorescence spectra to be changed. When Pb2+, a quenching metal ion, is added to 1 or 2, their pyrene monomer emission is enhanced with their excimer emission quenched, which is due to conformational changes of the facing carbonyl groups as well as to the participation of the ethyleneamine into the three-dimensional Pb2+ ion encapsulation. In contrast, upon addition of alkali metal ions to the 1 and 2, both monomer and excimer emissions are observed to increase, which is attributable to the CHEF effect and the reta...
82 citations
TL;DR: This study suggests that the time-dependent density functional theory method can be used to characterize the potential energy surfaces and the energetics of aromatic excimers with reasonable accuracy.
Abstract: A theoretical characterization of the potential energy surfaces of the singlet benzene excimer states derived from the B2u monomer excited state has been performed using time-dependent density functional theory. The excited-state potential energy surfaces were initially characterized by computations along the parallel and perpendicular intermolecular translational coordinates. These calculations predict that the lowest excited state for parallel translation is bound with a minimum at 3.15 angstroms and with a binding energy of 0.46 eV, while the perpendicular translational coordinate was essentially found to be a repulsive state. At the calculated minimum distance, the effect of in-plane rotation, out-of-plane rotation, and slipped-parallel translation were examined. The rotational calculations predict that deviations from the D6h geometry lead to a destabilization of the excimer state; however, small angular variations in the range of 0 degrees -10 degrees are predicted to be energetically feasible. The slipped-parallel translational calculations also predict a destabilizing effect on the excimer state and were found to possess barriers to this type of dissociation in the range of 0.50-0.61 eV. When compared to experimentally determined values for the benzene excimer energetics, the calculated values were found to be in semiquantitative agreement. Overall, this study suggests that the time-dependent density functional theory method can be used to characterize the potential energy surfaces and the energetics of aromatic excimers with reasonable accuracy.
TL;DR: In this article, the nature of the electronically excited states of He clusters and their relaxation mechanisms are investigated by spectroscopy using monochromatized synchrotron radiation.
Abstract: The nature of the electronically excited states of He clusters and their relaxation mechanisms are investigated by spectroscopy using monochromatized synchrotron radiation. Time correlated fluorescence excitation and energy resolved luminescence spectra of the clusters are recorded in separate wavelength ranges. The size of the clusters and the isotopic constitution is also varied. The spectral features are analysed and discussed particularly with regard to the high lying states and their possible Rydberg nature. While Rydberg states seem not to exist in the interior region of large clusters there is experimental evidence that sharp lines in the spectrum are either due to He Rydberg atoms or excimer molecules in high vibrational states bound at the surface of large clusters or due to very small positively charged clusters with the Rydberg electron outside. The spectra of large 3He clusters exhibit a larger contribution of Rydberg lines than 4He clusters. He clusters also emit fluorescence at energies above the ionization energy of He atoms. This is attributed to the barrier for the injection of electrons into the conduction band which was found to be 1.35 eV for 4He and 0.95 eV for 3He clusters, respectively.
TL;DR: The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation, which can be considered as a characteristic to validate the use of ligand L1 as a sensor for a given metal.
Abstract: A new fluorescent macrocyclic structure (L1) bearing two naphthalene units at both ends of a cyclic polyaminic chain containing two phenanthroline units was investigated with potentiometric and fluorescence (steady-state and time-resolved) techniques. The fluorescence emission spectra show the simultaneous presence of three bands: a short wavelength emission band (naphthalene monomer), a middle emission band (phenanthroline emission), and a long-wavelength band. All three bands were found to be dependent on the protonation state of the macrocyclic unit (including the polyaminic and phenanthroline structures). The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation. This is determined by comparison with the excimer emission formed by intermolecular association of 1,10-phenanthroline. With ligand L1, excimer formation occurs only at pH values above 4. At very acidic pH values, the protona...
TL;DR: A looped-back model of apoE4 is proposed in lipid-bound state, including spherical lipoprotein particles, wherein residues Arg-61 and Glu-255 are proximal to one another.
TL;DR: In this paper, a triad with tetrathiafulvalene (TTF) and pyrene units could be reversibly modulated by the different oxidation states of the TTF unit.
Abstract: The ratio of monomer and excimer emissions of a triad 1 with tetrathiafulvalene (TTF) and pyrene units could be reversibly modulated by the different oxidation states of the TTF unit. The working mechanism of this new fluorescence switch was demonstrated to be the collective result of the tunable photoinduced electron transfer and resonance energy transfer processes.
TL;DR: The galleries of an Mg-Al layered double hydroxide have been functionalized by intercalation of carboxymethyl beta-cyclodextrin cavities and two types of included naphthalene molecules have been identified: a preformed excimer-like species characterized by the absence of rise time in decay measurements and a monomeric species that is incapable of excimer formation due to the presence of suitably located includednaphthalenes in its proximity.
Abstract: The galleries of an Mg-Al layered double hydroxide have been functionalized by intercalation of carboxymethyl, \beta -cyclodextrin cavities. The anchored cavities form a random array of identical-sized hydrophobic nanopockets arranged in a bilayer fashion in the interlamellar space of the layered solid. Naphthalene molecules have been included within these cavities by partitioning from a polar solvent. The fluorescence from the included naphthalene shows an unusual behaviorsthe excimer to monomer emission intensity decreases with increasing concentration of included naphthalene. This is shown to be a consequence of the absence of translational mobility of the naphthalene-cyclodextrin adduct in the functionalized solid. Two types of included naphthalene have been identified: a preformed excimer-like species characterized by the absence of rise time in decay measurements and a monomeric species that is incapable of excimer formation due to the absence of suitably located included naphthalenes in its proximity. The concentration of each species and the enthalpy for excimer formation have been determined from the temperature variation of fluorescence intensities.
TL;DR: Calculations indicate that the sandwich conformer of BFM in the singlet ground state is unstable, whereas that in the triplet excited state has a bound state, being very slightly higher in internal and Gibbs free energies than that of the lowest state of the near-orthogonal conformer.
Abstract: A concerted computational and experimental study has been undertaken to probe the conformational structure and excited-state dynamics of bis(9-fluorenyl)methane (BFM). We have observed that the relative intensity of the delayed excimer fluorescence of BFM is greatly enhanced in comparison with that of the normal fluorescence. This is presumably because the relative concentration of the triplet excimer is enhanced in comparison with the singlet excimer. B3LYP DFT/6-31G(d) calculations indicate that the sandwich conformer of BFM in the singlet ground state is unstable, whereas that in the triplet excited state has a bound state, being very slightly higher in internal and Gibbs free energies than that of the lowest state of the near-orthogonal conformer.
TL;DR: The thermodynamic driving force for the intrapolymeric association was found to be dependent on a balance between hydrophobic and electrostatic interactions, which are dependent on the pH, temperature, andhydrophobic content of the polymer.
Abstract: Steady-state and time-resolved fluorescence studies were performed on aqueous solutions of poly(acrylic acid) hydrophobically modified with two very different levels of naphthalene (Np). It is demonstrated that unique information on association phenomena involving hydrophobe-modifed polymers can be obtained from an extended fluorescence study by using data for a less-modified polymer as a reference. For the more highly modified polymer, the presence of excited-state (as well as ground-state) dimers in addition to monomer emission due to locally excited naphthalene gives evidence for hydrophobic association between naphthalene groups. This association becomes, as expected, much less important at higher pH due to the electrostatic repulsion between different chain segments. However, it is noted that even at high pH there is a significant self-association. The coexistence of static and dynamic quenching phenomena of the Np monomer label was also revealed in the time-resolved fluorescence data. The data are compatible with the existence of two types of monomers and one excimer and suggest that the essential contribution to the monomer emission comes from isolated chromophores, whereas excimer formation arises from both a dynamic route (excited Np chromophores able to produce a dynamic excimer) and a static route (excitation of ground-state Np dimers). At room temperature, the dissociative reaction, excimer-to-monomer, can be neglected, and thus the rate constant for excimer formation and decay could be obtained with and without considering the influence of preformed dimers. Temperature has shown to induce different behavior in the polymer photophysics. In the case of the less-labeled polymer, the decays were found to be single-exponential with the fluorescence lifetime decreasing with increasing temperature. From the temperature dependence of the steady-state fluorescence data, the activation energy for excimer formation and the binding energy of the excimer were evaluated at different pH values, through the Stevens-Ban-type plots of the excimer-to-monomer intensity ratio. With the time-resolved data, measured in the temperature range of 5-60 degrees C, it was possible to extract the intrinsic activation energies for excimer formation. The thermodynamic driving force for the intrapolymeric association was found to be dependent on a balance between hydrophobic and electrostatic interactions, which are dependent on the pH, temperature, and hydrophobic content of the polymer.
TL;DR: The photophysical properties of a series of triply bridged [3.3.n]Cz molecules showed that relative configurations of carbazole moieties in the ground state were preserved even in the excimer states, and intramolecular excimer emission was shown.
Abstract: The photophysical properties of a series of triply bridged [3.3.n](3,6,9)carbazolophanes ([3.3.n]Cz, n = 3, 4, 5, 6) were studied as a model compound for a fully overlapped carbazole excimer. In these [3.3.n]Cz molecules, a plane angle of the two carbazole moieties changed systematically from nearly parallel to oblique, with increases in the length of the methylene chain n bridging at the 9-position of each carbazole ring. Absorption bands of [3.3.n]Cz showed the blue-shift and the splitting for 1La ← 1A and 1Lb ← 1A transition bands of the reference carbazole monomer, respectively. These spectral changes in [3.3.n]Cz were explained by Kasha's molecular exciton theory with the distance r and dihedral angle θ between the carbazole moieties in the ground state. In both liquid and glass matrixes, [3.3.n]Cz showed intramolecular excimer emission. The emission peak wavelength changed from 409 nm (n = 6) to 480 nm (n = 3) depending on r in the ground state. The dependence of the peak wavelength on r clearly sho...
TL;DR: Very short lifetimes of the lowest excited singlet (S1) state of benzophenone and p-hydroxybenzophenone (HOBP) suggest that they have π* character in all kinds of solvents as discussed by the authors.
Abstract: Very short lifetimes (a few picoseconds) of the lowest excited singlet (S1) state of benzophenone (BP) and p-hydroxybenzophenone (HOBP) suggest that they have π* character in all kinds of solvents. However, in the case of the p-amino-substituted benzophenones (ABPs), the nature of the S1 state, whether it is n–π* or π–π*, depends on the nature of the solvent and the identity of the substituent groups. The lowest excited triplet (T1) state of BP has nπ* character in all kinds of solvents and hence phosphorescence decay is short (a few ms). The T1 state character of HOBP and ABP’s are solvent dependent. In a few cases dual exponential decay of phosphorescence indicates that n–π* and π–π* triplet states lie close to each other. The π–π* type of T1 state has longer phosphorescence lifetime (a few tens of ms). Investigations of the ultrafast relaxation dynamics of 4-N,N-dimethylaminobenzophenoene (DMABP) in different kinds of solvents of varying polarities and viscosities reveal that conversion of the locally excited (LE) state to the twisted intramolecular charge transfer (TICT) state by twisting of the dimethylanilino group is the major process, which is responsible for the efficient non-radiative relaxation mechanism of the S1 state of this molecule and solvation dynamics plays a minor role in it. In self-quenching interaction between the triplet state and its ground state, the n–π* kind of T1 state plays the major role and no triplet exciplex is involved as an intermediate. The T1 state of BP is equally reactive towards hydrogen atom abstraction reaction with the ground state of each of the ABPs either by direct hydrogen atom transfer or by a chargetransfer-coupled proton-transfer mechanism. Exciplex formation has been observed only in the case of the reaction between the T1 state of BP and DMABP.
TL;DR: Hexakis(2-naphthyloxy)cyclotriphosphazene showed an interesting emission behavior between its monomer and excimer forms, the latter nearly completely dominating in water.
TL;DR: The photophysical behavior of a hydrophobically tailored water-soluble polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), has been studied in aqueous buffered bovine serum albumin (BSA) and human serumalbumin (HSA) media and the binding interaction has been shown to have a prominent role on the steady state fluorescence anisotropy of the two emission bands.
Abstract: The photophysical behavior of a hydrophobically tailored water-soluble polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), has been studied in aqueous buffered bovine serum albumin (BSA) and human serum albumin (HSA) media In buffered aqueous solution the polymer shows dual emission corresponding to the monomer and the excimer of pyrene moiety The relative intensity of the monomer to the excimer emission shows interesting variation with the addition of BSA and HSA and is indicative of significant interaction of these albumin proteins with the polymer The binding interaction has been shown to have a prominent role on the steady state fluorescence anisotropy of the two emission bands Attempt has been made to determine the micropolarities of the protein microenvironments from a comparison of the variation of the monomer to excimer relative fluorescence intensities of the probe in water-dioxane mixtures with varying composition
TL;DR: In this paper, a novel fluorescence film sensor was designed and prepared to improve the performance of the film sensors reported recently for dicarboxylic acids, which showed combined monomer and excimer emission of pyrene (Py) both in wet and dry states.
Abstract: A novel fluorescence film sensor was designed and prepared to improve the performance of the film sensors reported recently for dicarboxylic acids. The reported sensors suffered from slow response and low sensitivity to the analytes. Simple elongation of the spacer by using 1,4-diaminobutane instead of 1,2-diaminoethane or 1,3-diaminopropane improved the performances of the film sensors greatly. The response time was reduced from tens of minutes, or even hundreds of minutes to less than 10 min, and the sensitivity was improved from more than 10 mM to tens of micro-molars. Similar to the reported films, the new film also shows combined monomer and excimer emission of pyrene (Py) both in wet and dry states, and both the emissions in the monomer and excimer regions increases along with addition of dicarbonxylic acids. The excimer formed in the present film, however, mainly adopts, especially in aqueous phase, sandwich-like structure. The differences in the photophysical behavior and the improvement in the sensing performance mentioned above have been attributed to the increase in the length of the spacer, which makes the spacer in the present film more flexible and gives the sensing molecule more chance to form perfect excimers. Furthermore, the response of the film to dicarboxylic acids is well reversible.
TL;DR: Efficient monomer and excimer emission from various donor-acceptor substituted phenylethynes (PE), which are known as efficient electrogenerated chemiluminescent molecules, was observed with time-resolved fluorescence measurement during the pulse radiolysis in benzene.
Abstract: Efficient monomer and excimer emission from various donor−acceptor substituted phenylethynes (PE), which are known as efficient electrogenerated chemiluminescent molecules, was observed with time-resolved fluorescence measurement during the pulse radiolysis in benzene. On the basis of the transient absorption and emission measurements, and steady-state measurements, the formation of PE in the singlet excited state (1PE*) and the excimer (1PE2*) can be interpreted by the charge recombination between the PE radical cation (PE•+) and the PE radical anion (PE•-) which are generated initially from the radiolytic reaction in benzene. It is suggested that the positive and negative charges are localized on the donor and acceptor moieties in the radical cation and anion, respectively. This mechanism is reasonably explained by the relationship between the annihilation enthalpy changes (−ΔH‘°) and singlet excitation energies of donor-substituted phenyl(9-acridinyl)ethynes (1a-e). In addition to the monomer emission,...
TL;DR: On the whole, using both steady-state and time-resolved fluorescence parameters, and by comparing data for a polymer with a small number of hydrophobes with a more highly modified one, it is possible in great detail to demonstrate how association is controlled by solvent quality for the hydrophobia and by the distance between hydrophOBes.
Abstract: The solution properties of two water-soluble polymers, poly(acrylic acid) (PAA), covalently labeled with the fluorescent hydrophobic dye naphthalene (Np), have been investigated in water:organic solvent mixtures. The naphthalene chromophores have been randomly attached, onto the polymer, with two different degrees of labeling. Fluorescence measurements (steady-state and time-resolved) have been used to follow the photophysical behavior of the polymers and consequently report on the self-association of the polymers in the mixed organic (methanol or dioxane):aqueous solutions. The emission spectra of the high-labeled Np PAA reveal the presence of monomer and excimer bands whereas with the low-labeled polymer only monomer emission is observed. The excitation spectra collected at the monomer and excimer emission bands show significant differences, depending on the water content of the mixture, which indicate the simultaneous presence of preformed and dynamic dimers as routes to excimer formation. The time-res...
TL;DR: In this paper, the authors measured the fluorescence spectra of pyrene doped in a polymer film at various temperatures in the region of 70-293 K and found three types of partially overlapped excimer fluorescence exist at low temperatures for pyrene in a PMMA film at high concentrations.
TL;DR: In this article, the finite elements analysis using ANSYS® (8.0) of the heteroepitaxial SiGe alloy formation induced by excimer lasers is presented, and the numerical simulation of the temperature distribution induced by KrF excimer laser (energy densities 0.50 <Φ< 0.55 J/cm 2 ) on thin amorphous Ge films (10 nm thick) deposited on Si(1 0 0) substrates is obtained.
TL;DR: In this article, a new anthracene based fluorescent anion receptor bearing two imidazolium units linked by methylene spacers at 9,10 positions has been synthesized.
Abstract: New anthracene based fluorescent anion receptor bearing two imidazolium units linked by methylene spacers at 9,10-positions has been synthesized. Complexation behavior and fluorescent properties of the receptor with inorganic anions (Cl - , Br - , I - , NO/, HSO 4 - , and H 2 PO 4 - ) in acetonitrile were investigated by 1 H NMR spectrometric and fluorimetric titrations, and fluorescence lifetime measurement. At low receptor concentration level (0.1 μM), fluorescence of the receptor was quenched by formation of 1:1 host-guest complex with the anions. At relatively higher receptor concentrations (above 1.0 μM), Η 2 PO 4 - anion quenched the monomer emission mainly by the excimer formation due to anion-induced ground state aggregation. Fluorescence lifetime measurements revealed that quenching mechanisms are different between halide ions and oxoanions.
TL;DR: In this paper, a study of excimer emission from copolymers of dibutylfluorene and butylphenylphenoxazine was conducted, and it was shown that the observed differences in excimer intensity between PL and electroluminescence spectra are neither solely due to local heating by electric current nor to differences in the exciton density, but instead, different nature of the excitations upon photoexcitation and excitation by passing current has to be considered to explain the different behavior.
Abstract: We report a study of excimer emission from copolymers of dibutylfluorene and butylphenylphenoxazine. Temperature dependence of photoluminescence (PL) spectra measured from room temperature to above glass transition temperature, and excitation power dependence of PL spectra reveal that the observed differences in excimer intensity between PL and electroluminescence spectra are neither solely due to local heating by electric current nor to differences in exciton density. Instead, different nature of the excitations upon photoexcitation and excitation by passing current has to be considered to explain the different behavior.