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.     

含芘荧光化学敏感器化合物同小牛胸腺DNA分子间的相互作用

研究了含芘荧光化学敏感器分子被ctDNA猝灭的荧光光谱.ctDNA分子对该化学敏感器中芘的激发单体,激基缔合物都有猝灭作用.对激发单体的猝灭速度顺序为;化合物(2)>化合物(1)>芘丁酸>化合物(3);对激基缔合物的猝灭速度顺序为;化合物(2)化合物(3).由得到的荧光猝灭数据,可按公式(2)求得荧光化学敏感器分子与ctDNA分子相互作用的稳定常数.发现化合物(2)与ctDNA分子间有着最强的相互作用能力.按ctDNA和含芘荧光化学敏感器的分子结构、构型以及分子内原子-原子的间距等提出了ctDNA分子与该荧光化学敏感器的作用模型,并对上述结果进行了初步解释.     

Synthesis and characterization of novel pyrene-dendronized porphyrins exhibiting efficient fluorescence resonance energy transfer: optical and photophysical properties

A novel series of pyrene dendronized porphyrins bearing two and four pyrenyl groups (Py(2)-TMEG1 and Py(4)-TMEG2) were successfully synthesized. First and second generation Fréchet type dendrons (Py(2)-G1OH and Py(4)-G2OH) were prepared from 1-pyrenylbutanol and 3,5-dihydroxybenzyl alcohol. These compounds were further linked to a trimesitylphenylporphyrin containing a butyric acid spacer via an esterification reaction to obtain the desired products. Dendrons and dendronized porphyrins were fully characterized by FTIR and (1)H NMR spectroscopy and their molecular weights were determined by matrix-assisted laser desorption ionization time of flight mass spectrometry. Their optical and photophysical properties were studied by absorption and fluorescence spectroscopies. The formation of dynamic excimers was detected in the pyrene-labeled dendrons, with more excimer being produced in the higher generation dendron. The fluorescence spectra of the pyrene dendronized porphyrins exhibited a significant decrease in the amount of pyrene monomer and excimer emission, jointly with the appearance of a new emission band at 661 nm characteristic of porphyrin emission, an indication that fluorescence resonance energy transfer (FRET) occurred from one of the excited pyrene species to the porphyrin. The FRET efficiency was found to be almost quantitative ranging between 97% and 99% depending on the construct. Model Free analysis of the fluorescence decays acquired with the pyrene monomer, excimer, and porphyrin core established that only residual pyrene excimer formation in the dendrons could occur before FRET from the excited pyrene monomer to the ground-state porphyrin core.     

Organosilane polymers: Synthesis and photochemical and photophysical behavior of poly[dimethyl-co-methyl(1-naphthyl)silylene]

A meltable, partially crystalline silane copolymer, PSN, containing dimethylsilylene and methyl(1-naphthyl) silylene units was synthesized and characterized. The polymer has a high molecular weight, is appreciably soluble in common solvents and is photoactive. The emission properties of PSN, under stationary and nonstationary conditions, were studied in dilute THF solution. PSN is the first organosilane polymer showing an intense intramolecular excimer emission in addition to monomer and intramolecular charge transfer (CT) fluorescence. It is shown that the ratio of excimer to monomer fluorescence can be used to monitor the UV induced degradation of the polymer.     

A new pyrene-based fluorescent probe for the determination of critical micelle concentrations

A new pyrene-based fluorescent probe for the determination of critical micelle concentrations (CMC) is described. The title compound 1 is obtained in five steps, starting from pyrene. Fluorescence spectroscopic properties of 1 are studied in homogeneous organic solvents and aqueous micellar solutions. In a wide range of organic solvents, probe 1 exhibits a characteristic monomer emission of the pyrene fluorophore, with three distinct peak maxima at 382, 404, and 425 nm. The spectra change dramatically in aqueous solution, where no monomer emission of the pyrene fluorophore is detected. Instead, only strong excimer fluorescence with a broad, red-shifted emission band at lambda(max) = 465 nm is observed. In micellar aqueous solution, a superposition of the monomer and excimer emission is found. The appearance of the monomer emission in micellar solution can be explained on the basis of solubilization of 1 by the surfactant micelles. The ratio of the monomer to excimer fluorescence intensities of 1 is highly sensitive to changes in surfactant concentration. This renders 1 a versatile and sensitive probe molecule for studying the micellization of ionic and nonionic surfactants. For a representative selection of common surfactants, the critical micelle concentrations in aqueous solution are determined, showing excellent agreement with established literature data.     

A calixarene based fluorescent Sr2+ and Ca2+ probe

A fluorescent probe, PyCalix, which has two pyrene moieties at the lower rim of a calix[4]arene fixed in the cone conformation was synthesized and its complexation behavior with alkali and alkaline earth cations was studied by fluorescence spectrometry. The compound showed intramolecular excimer emission at approximately 480 nm in the fluorescence spectra. Upon complexation with alkaline earth metal cations, a decrease of excimer emission was observed. The decrease of excimer emission was accompanied by an increase of monomer emission of pyrenes at 397 nm. The order of complexation constants of PyCalix with metal ions was Sr(+ approximately Ca2+ > Ba2+ > Mg2+ > K+ > Na+ > Cs+ for all reagents. PyCalix doped polyvinyl chloride (PVC) membrane was fabricated and our results showed that this membrane can be used for selective detection of Sr2+.     

Ratiometry of monomer/excimer emissions of dipyrenyl calix[4]arene in aqueous media

Variations in the ratio of monomer/excimer emissions from pyrenyl groups bound to a calix[4]arene through facing carboxamidomethyl substituents have been investigated in H₂O/CH₃CN mixtures. Above a level of 50% H₂O, monomer emission declines and the excimer emission concomitantly increases. DFT calculations support the argument that disruption of intramolecular NHO bonds by water results in a geometry, which favors contact of the pyrene units and thus a strong excimer emission. Addition of Fe(III) to a H₂O/CH₃CN (4:1, v/v) solution of 1 at pH 6.1 quenches both monomer and excimer emissions through electron transfer (eT) from excited pyrene to the metal ion.     

Effect of side-chain length on the side-chain dynamics of alpha-helical poly(L-glutamic acid) as probed by a fluorescence blob model

Two series of pyrene-labeled poly(glutamic acid) (Py-PGA) were synthesized utilizing two different linkers for pyrene attachment, namely 1-pyrenemethylamine (PMA) and 1-pyrenebutylamine (PBA). Several Py-PGAs were synthesized for each series with pyrene contents ranging from 4 to 15 mol %. Py-PGA forms a rigid alpha-helix in DMF that effectively locks the backbone in place, thus enabling only side-chain or linker motions to be monitored by time-resolved fluorescence. Time-resolved fluorescence decays were acquired for the pyrene monomer of the Py-PGA constructs and the fluorescence blob model (FBM) was used to quantify the dynamics of the different linkers connecting pyrene to the backbone. Nitromethane was used to shorten the lifetime of the pyrene monomer, in effect controlling the probing time of the pyrene group, from 50 to 155 ns for PGA-PBA and from 50 to 215 ns for PGA-PMA. The FBM analysis of the fluorescence decays led to the conclusion that excimer formation around the rigid alpha-helix backbone takes place in a compact environment. The number of glutamic acid units within a blob, N blob, decreased only slightly with decreasing probing time for both Py-PGA constructs as a result of the compact distribution of the chromophores around the alpha-helix. The PGA alpha-helix was modeled using Hyperchem software and the ability of two pyrene groups to encounter was evaluated as they were separated by increasing numbers of amino acids along the alpha-helix. The number of amino acids required for two pyrenes to lose their ability to overlap and form excimer matched closely the N blob values retrieved using the FBM.     

Intramolecular pi-stacking interaction in a rigid molecular hinge substituted with 1-(pyrenylethynyl) units

Synthesis of a tetrakis(1-pyrenylethynyl)-substituted rigid hinge-like molecule (1) is described. The intramolecular pi-stacking interaction of the pyrene units is studied by 1H NMR and fluorescence spectroscopy. Due to intramolecular pi-stacking interactions, chemical shifts of the pyrene protons in 1 are highly shielded in the NMR spectrum. Fluorescence from the static excimer state is observed due to pi-stacking interactions among the pyrene units in the ground state of 1. Based on the spectroscopic evidence, conformations and dynamics of 1, arising from the hindered rotation of the major axis, are proposed.     

Chloride selective calix[4]arene optical sensor combining urea functionality with pyrene excimer transduction

A neutral 2-site chloride selective compound has been developed (3), based on a 1,3-alternate tetrasubstituted calix[4]arene providing a preorganized supramolecular scaffold. The resultant supramolecular cavity is among the first to combine urea functional groups bridged with single methylene spacers to pyrene moieties. It combines a naturally and synthetically proven H-bonding system with the elegant ratiometric fluorescent signaling properties of an intramolecular pyrene excimer system, triggered by conformational changes upon anion coordination. The excimer emission of 3 is quenched, with a simultaneous rise in the monomer emission solely by the chloride anion among a wide variety of anions tested. 3 has an association constant of 2.4 x 10(4) M(-1) with chloride. The suitability and advantages of ratiometric optical sensor compounds like 3 for use in practical sensor devices is discussed. 3 has an LOD of 8 x 10(-6) M with chloride in acetonitrile-chloroform (95:5 v/v). A dynamic fluorescence study revealed a response time of < 3 s. A recently developed and simple HPLC-based purification method complimented conventional organic work up methods to yield pure product.     

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.     

Electric field effects on absorption and fluorescence spectra of trimethylsilyl- and trimethylsilylethynyl-substituted compounds of pyrene in a PMMA film

External electric field effects on absorption and fluorescence spectra of 1,3,6,8-tetrakis(trimethylsilyl)pyrene and 1,3,6,8-tetrakis(trimethylsilylethynyl)pyrene (TMSPy and TMS(E)Py, respectively) have been examined in a poly(methyl methacrylate) (PMMA) film at various concentrations at various temperatures. TMS(E)Py preferentially forms an aggregate in a PMMA film, as the concentration increases, indicating that the acetylenic groups enhance the pi-pi interactions between pyrene molecules. The change in molecular polarizability following excitation has been determined both for the monomer and for the aggregate, based on the electroabsorption spectra. The change in molecular polarizability following emission has also been determined in both compounds, based on the electrofluorescence spectra. TMSPy exhibits two excimer fluorescence emissions at high concentrations which are ascribed to the partially overlapping excimer and the sandwich-type excimer, respectively, besides the monomer fluorescence emitted from the locally excited state. The sandwich-type excimer fluorescence as well as monomer fluorescence is quenched by an electric field, whereas the fluorescence of the partially overlapping excimer is enhanced by an electric field. Excimer fluorescence of TMS(E)Py, which arises from the sandwich-type excimer, is quenched by an electric field at any temperature. Only one species of the partially overlapping excimer is confirmed in TMSPy, while no partially overlapping excimer is confirmed in TMS(E)Py.     

7-Deazapurine and 8-aza-7-deazapurine nucleoside and oligonucleotide pyrene "click" conjugates: synthesis, nucleobase controlled fluorescence quenching, and duplex stability

7-Deazapurine and 8-aza-7-deazapurine nucleosides related to dA and dG bearing 7-octadiynyl or 7-tripropargylamine side chains as well as corresponding oligonucleotides were synthesized. "Click" conjugation with 1-azidomethyl pyrene (10) resulted in fluorescent derivatives. Octadiynyl conjugates show only monomer fluorescence, while the proximal alignment of pyrene residues in the tripropargylamine derivatives causes excimer emission. 8-Aza-7-deazapurine pyrene "click" conjugates exhibit fluorescence emission much higher than that of 7-deazapurine derivatives. They are quenched by intramolecular charge transfer between the nucleobase and the dye. Oligonucleotide single strands decorated with two "double clicked" pyrenes show weak or no excimer fluorescence. However, when duplexes carry proximal pyrenes in complementary strands, strong excimer fluorescence is observed. A single replacement of a canonical nucleoside by a pyrene conjugate stabilizes the duplex substantially, most likely by stacking interactions: 6-12 °C for duplexes with a modified "adenine" base and 2-6 °C for a modified "guanine" base. The favorable photophysical properties of 8-aza-7-deazapurine pyrene conjugates improve the utility of pyrene fluorescence reporters in oligonucleotide sensing as these nucleoside conjugates are not affected by nucleobase induced quenching.     

一种含芘葡萄糖衍生物的合成及其胶凝行为

合成并表征了一种荧光活性小分子胶凝剂——芘磺酰基-丙二胺-葡萄糖(PSDAPG), 考察了其在36种常见溶剂中的胶凝行为. 结果发现, PSDAPG可使其中16种溶剂胶凝. 对癸醇, PSDAPG表现出罕见的超级胶凝能力, 室温下最低胶凝浓度(MGC)达7.0×10-4 g·mL-1. 此外, PSDAPG还是一种既可胶凝水又可胶凝有机溶剂的双性胶凝剂. 扫描电镜(SEM)、傅立叶变换红外光谱(FTIR)、核磁共振(1HNMR)和荧光光谱研究表明,在不同溶剂中, PSDAPG具有不同的聚集结构, 除了芘基之间的疏水π-π堆积作用外, 氢键作用是PSDAPG自发形成三维网络结构的重要驱动力. 实验研究还表明, 溶液态和凝胶态的PSDAPG荧光光谱均同时呈现芘的单体荧光和激基缔合物荧光光谱特征, 但两者的光谱形貌差异显著. 随凝胶的形成, 体系单体荧光发射增强, 激基缔合物荧光发射减弱,表明形成的三维网络结构阻碍了PSDAPG中芘单元的运动性, 使得以Birks途径形成激基缔合物的效率降低.     

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.     

Polarization of the monomer and excimer fluorescence of pyrene derivatives in liquid-crystalline hosts

The monomer and excimer fluorescence polarization of 4,9-disubstituted pyrenes with molecular long axes nearly perpendicu- lar to the pyrene skeleton were measured in a nematic liquid crystal. By comparison with unsubstituted pyrene it is found that the excimer transition moment is oriented parallel to the sandwich plane and perpendicular to the pyrene long axis.     

Adduct Formation Between γ-Cyclodextrin and the Bifluorophore 1,3-Bis(1-pyrenyl)propane

The complexation of the bifluorophore 1,3-bis(pyrenyl)propane with γ-cyclodextrin in water has been studied by means of steady state and time-resolved fluorescence spectroscopy. It was found that in the association with γ-cyclodextrin the propane chain of 1,3-bis(pyrenyl)propane folds and the two pyrene units enter the same cyclodextrin cavity where they form weakly bound ground state dimers, which upon excitation emit excimer fluorescence. In addition to this 1:1 excimer emitting complex, two more complexes were detected, which emit monomer pyrene fluorescence. One has 1:1 stoichiometry, i.e. isomeric to the previous complex, and the other, with 2:1 stoichiometry, is comprised of two γ-cyclodextrin units and one 1,3-bis(pyrenyl)propane.     

芘在改性硅胶上的光物理研究——以芘为探针研究改性硅胶的表面特性

研究了芘在正十碳烷氧基和三甲基硅氧基改性硅腔表面上的荧光光谱和寿命。在这二种硅胶上,激基缔合物是由基态聚积体直接受光和受激发的单分子和基态的单分子所形成、在硅胶≡Si—O—C_(10)H_(21)-n上比在硅胶≡Si—O—SiMe_3上所形成的聚积体较少。化学改性与物理改性相结合可使芘在较大的浓度范围内主要以单分子分散。激基缔合物的形成主要是由动力学过程所控制。研究了温度对芘的荧光光谱和寿命的影响。激基缔合物形成过程的活化能约为7kcal mol~(-1)。讨论了环境对单分子荧光光谱结构的影响。     

Fluorescence quenching of pyrene monomer and excimer by CH3I

The fluorescence quenching rate constants of pyrene monomer and excimer by CH₃I were obtained at several temperatures in methylcyclohexane. Both quenching processes are kinetically controlled, allowing insight on the mechanism of quenching. The rate constants have both temperature-independent and temperature-dependent components. The temperature-independent component for both monomer and excimer fluorescence is consistent with quenching due to enhanced intersystem crossing to a lower energy triplet state. The monomer temperature-dependent component comes from the enhancement of the intersystem crossing to a higher energy triplet state. The thermally activated excimer quenching is associated with the excimer dissociation step to give a pyrene in a second triplet state plus a ground state pyrene molecule.     

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.