荧光法测定N-(α-烷苯氧基)十四酰基牛磺酸钠的临界胶束浓度

研究了一类以苯氧基作疏水支链的新型阴离子表面活性剂——N-(α-烷苯氧基)十四酰基牛磺酸钠(SAPTT)水溶液的紫外吸收光谱、探针(芘)稳态荧光发射光谱及自身稳态荧光发射光谱性质.研究结果表明,荧光探针(芘)法和自身稳态荧光法可用来测定这类表面活性剂的临界胶束浓度(CMC),且测定结果与表面张力法(吊片法)接近;与荧光探针(芘)法相比,对于所研究体系,自身稳态荧光法的灵敏度和准确性均较高,所测得CMC结果与表面张力法(吊片法)能较好地吻合.     

Enhancement of Förster Energy Transfer within a Microspherical Cavity

Energy transfer from pyrene to perylene molecules co-doped within a poly(methyl methacrylate) latex microsphere was drastically accelerated relative to free space. Fluorescence spectra of the microspheres showed that the relative emission intensities of pyrene and perylene changed with the sphere diameter. Analyses of emission decay profiles clarified that F?rster-type energy-transfer processes were induced and that the transfer rates increased within the microspherical cavity. This enhancement can be ascribed not only to the quantum electrodynamic effects on the pyrene emission rate, but also the cavity effect of increasing the overlapping factor between donor emission and acceptor absorption spectra.     

Guest-responsive excimer fluorescence of β-cyclodextrin bearing a pendant group with two pyrene moieties

β-Cyclodextrin derivative 1 , bearing a group with two pyrene moieties, exhibits predominant excimer emission in a 20% DMSO aqueous solution. In spite of the fact that pyrene is too large to be included in the β-cyclodextrin cavity and consequently both pyrene moieties are located outside the cavity, 1 varies the excimer emission intensity through the formation of inclusion complexes with guest species, thus acting as a chemosensor for molecular recognition.     

Computer simulation study on the structural-optical related properties of a pyrene-functionalized fluorescent film

Molecular dynamics simulations were carried out to investigate the structural properties and the structure related optical properties of a pyrene-functionalized film and also the film in the presence of nitrobenzene. It has been shown that at equilibrium (1) the pyrene molecules of the film, of which the fluorophore molecules have been attached to a glass plate surface via relatively long flexible spacers, adopt quasi-coplanar structures; (2) the distance between a pair of pyrene rings populates from 4 A to longer than 10 A, but quite a large number of pyrene molecules populate within distances between 4 and 5 A, indicating that the fluorescence of the film should be characterized by both monomer emission and excimer emission; (3) introduction of nitrobenzene into the system results in a decrease of the population of pyrene molecules within the distances suitable for the formation of excimers, suggesting that excimer emission of the film would be decreased; and (4) the incoming nitrobenzene molecules insert themselves in between the previously formed coplanar structures of pyrene rings and form a complex with one of them. Considering that nitrobenzene is an electron-poor compound and nonfluorescent and that pyrene is an electron-rich one, it is expected that the formation of the complex must result in an excitation transfer from pyrene to nitrobenzene, provided that the distance between them and the orientations of them are reasonable. This indicates that the introduction of nitrobenzene not only decreases the number of excimers of pyrene but also quenches the monomer emission of the fluorophore. All the expectations from the simulation studies are basically consistent with the experimental observations.     

Dinuclear Diphosphine Complexes of Gold(I) Alkynyls,the Effects of Alkynyl Substituents onto Photophysical Behavior

A series of dinuclear diphosphine complexes of gold(I) alkynyls containing bis(diphenylphosphanyl)ethane/propane and alkynyl ligands with aromatic substituents (biphenyl, pyrene, and azobenzene) was synthesized and characterized using X‐ray crystallography and NMR spectroscopy. Photophysical parameters of the compounds obtained strongly depend on the nature of aromatic substituents in the alkynyl ligands. Azobenzene containing derivatives are non‐luminescent, whereas biphenyl and pyrene containing complexes display moderate emission both in solution and in solid state. The complexes with biphenyl substituents display strong heavy atom effect and show typical phosphorescent emission. In contrast, the complexes containing pyrene chromophore are fluorescent that points to the absence of spin orbit coupling in these systems, which additionally display static excimer emission in solid phase due to ground state π‐stacking of the pyrene moieties.     

Morphology-controllable synthesis of pyrene nanostructures and its morphology dependence of optical properties

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 discussed in detail.     

Pyrene-sensitised near-IR luminescence from ytterbium and neodymium complexes

Ytterbium and neodymium have been shown to exhibit sensitised emission following excitation of pyrene chromophores. Sensitised emission is demonstrated in self-assembled complexes and in azamacrocycle derivatives bearing pendent pyrene groups. Energy transfer in these systems is dependent on the nature of the link between the ligand and the complex.     

Excimer Emission of Pyrene-l-Butyric Acid in Aqueous Solution of Sodium Dodecyl Sulfonate below Critical Micelle Concentration

Excimer emission of ionic pyrene derivatives in ionic surfactant solutions has been observed. However, the reports were concerning on the excimer emission of charged pyrene derivatives in the presence of oppositely charged surfactant, in those cases the excimer formation was reasoned as surfactant induced aggregation of fluorophore through both hydrophobic and electrostatic interactions.     

Protease Probes that Enable Excimer Signaling upon Scission

Peptide‐based probes that fluoresce upon proteolytic cleavage are invaluable tools for monitoring protease activity. The read‐out of protease activity through pyrene excimer signaling would be a valuable asset because the large Stokes shift and the long lifetime of the excimer emission facilitate measurements in autofluorescent media such as blood serum. However, proteolytic cleavage abolishes rather than installs the proximity relationships required for excimer signaling. Herein, we introduce a new probe architecture to enable the switching on of pyrene excimer emission upon proteolytic scission. The method relies on hairpin‐structured peptide nucleic acid (PNA)/peptide hybrids with pyrene units and anthraquinone‐based quencher residues positioned in a zipper‐like arrangement within the PNA stem. The excimer hairpin peptide beacons afforded up to a 50‐fold enhancement of the pyrene excimer emission. Time‐resolved measurements allowed the detection of matrix metalloprotease 7 in human blood serum.     

Color-tunable fluorescent organogels: columnar self-assembly of pyrene-containing oligo(glutamic acid)s

New fluorescent gelators containing pyrene moieties and dendritic oligopeptides have been developed. These molecules self-assemble into 1D helical columnar structures that lead to the formation of 3D fibrous random networks. The resulting gel materials show monomer emission of pyrenes because the hydrogen-bonded array of the oligopeptide moieties greatly suppresses the formation of pyrene excimers. In contrast, in the sol states green excimer emission of the pyrenes is observed because of the dissociation of intermolecular hydrogen bonds. This is the first example of the reverse-mode color switching of fluorescence for supramolecular pyrene assemblies.     

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.     

A ratiometric fluorescent sensor for Ag(I) 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.     

Biphasic photochemistry: time-resolved spectra of adsorbed hydrocarbons

Time-resolved fluorescence spectra were measured for pyrene and naphthalene adsorbed on a silica gel surface using the time-correlated photon-counting technique Excimer-Iike emission was observed within an excitation lamp duration of a few nanoseconds with both pyrene and naphthalene. It is suggested, from the excitation spectra, that ground state complexes of the adsorbates are responsible for the formation of the excimer-like emission.     

Resolution of ultrafast pyrene excimer emission rise times in zeolites X and Y

Pyrene has been a favorite photophysical probe molecule for zeolite research because of its ability to exhibit both monomer and excimer emission upon excitation. This study combines the use of ultrafast time-resolved fluorescence spectroscopy with steady-state fluorescence spectroscopy to study the excimer emission of pyrene incorporated within zeolites LiY, NaY, KY and NaX. The effects of sealing technique and coincorporated solvents are also explored. Pyrene excimer emission is resolvable with the use of an ultrafast streak camera under all conditions examined in this study with a rise-time range of 6.8 to 16.0 picoseconds. For each zeolite sample the addition of cosolvents decreases the rise time, with a greater decrease for polar solvents than for a nonpolar solvent. The presence of a detectable rise time for excimer emission indicates that pyrene excimer formation is a dynamic process when pyrene is embedded within the cavities of zeolite host materials.     

The electrogenerated chemiluminescence of pyrene and some related compounds

The characteristics of the electrogenerated chemiluminescence in dimethylformamide of pyrene, 1,2-benzpyrene, 3,4-benzpyrene and dibenzo[a,lpyrene, dibenzo[a,i]pyrene, dibenzo [a,h]pyrene and dibenzo [b,l]pyrene generated with optimum conditions of applied potential are described. The appearance of emission at wavelengths longer than those expected from the excited singlet state of the hydrocarbons may be attributed to decomposition products. Pyrene and 3,4-benzpyrene exhibit long wavelength emission, however, which it is suggested may be due to excimer formation.     

Pyrene excimer signaling molecular beacons for probing nucleic acids

Molecular beacon DNA probes, containing 1-4 pyrene monomers on the 5' end and the quencher DABCYL on the 3' end, were engineered and employed for real-time probing of DNA sequences. In the absence of a target sequence, the multiple-pyrene labeled molecular beacons (MBs) assumed a stem-closed conformation resulting in quenching of the pyrene excimer fluorescence. In the presence of target, the beacons switched to a stem-open conformation, which separated the pyrene label from the quencher molecule and generated an excimer emission signal proportional to the target concentration. Steady-state fluorescence assays resulted in a subnanomolar limit of detection in buffer, whereas time-resolved signaling enabled low-nanomolar target detection in cell-growth media. It was found that the excimer emission intensity could be scaled by increasing the number of pyrene monomers conjugated to the 5' terminal. Each additional pyrene monomer resulted in substantial increases in the excimer emission intensities, quantum yields, and excited-state lifetimes of the hybridized MBs. The long fluorescence lifetime ( approximately 40 ns), large Stokes shift (130 nm), and tunable intensity of the excimer make this multiple-pyrene moiety a useful alternative to traditional fluorophore labeling in nucleic acid probes.     

Indium(III)-induced fluorescent excimer formation and extinction in calix[4]arene-fluoroionophores

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.     

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.     

Unique blue shift due to the formation of static pyrene excimer: highly selective fluorescent chemosensor for Cu

New binaphthyl derivatives bearing pyrene groups have been synthesized and studied as fluorescent chemosensors for Cu²⁺ ions. A unique blue shift along with fluorescent enhancement in pyrene excimer emission was observed, which were induced by the formation of a static pyrene excimer.