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.     

Fluorescent probe as reporter on the local structure and dynamics in hydrolysis-condensation process of organotrialkoxysilanes

To get some information on the aggregation behaviors of the products derived from different organotrialkoxysilanes, the hydrolysis-condensation processes of some organotrialkoxysilanes have been examined by means of pyrene as fluorescent probe. The organotrialkoxysilanes used in the research were n-octadecyltri-methoxysilane (ODTMS), n-octyltrimethoxysilane (OTMS), 3-glycidoxypropyltrimethoxysilane (GTMS), 3-methacryloxypropyltrimethoxysilane (MAPTMS), and propyltrimethoxy-silane (PTMS). The results show that pyrene as fluorescence probe can respond sensitively not only to the organization state of the hydrolysates but also to the change in the organization state during the condensation process. The organization states during the hydrolysis and condensation can be explained in terms of structures of the products. In the initial stage, the silanols with long organic chains are amphiphilic molecules, and such nature of the silanols can be compared to that of a surfactant. Therefore, the excimer emission of pyrene is extremely obvious because of such silanols being prone to form aggregates. In the case of silanols having short alkyl groups or epoxy groups, these silanols homogenously disperse in solution, which results in the appearance of an only monomer emission of pyrene. In the late stage, the fluorescence behavior of pyrene is also sensitive to structural evolution of the silicates. The fluorescence spectra of pyrene during the condensation of the silanols with short alkyl groups or epoxy groups are almost in silence, indicating that the condensation products, with a low condensation degree, homogeneously disperse in solution. For the silanols with long hydrophobic substituents in different lengths, the changes in fluorescence spectra of pyrene during the condensation are varied. Commonly, the excimer emission is noticeable, implying that the condensation products with high condensation degree inhomogenously disperse in solution. However, the relative excimer/monomer fluorescence intensity is alkyl chain-length dependent. The longer alkyl chains in the condensation products result in the appearance of the obvious excimer emission. These phenomena imply that the condensation degree of the products increases with the length of the alkyl chains. Additionally, the distorted spectrum of pyrene appears in the case of the organotrialkoxysilanes with side chain substituent, illustrating that the steric hindrance between the substituents can be monitored by fluorescence of pyrene. All these results are verified by the fluorescence-quenching measurements. The approach in the present study gives new insights into the local structure and dynamics in hydrolysis-condensation process of organotrialkoxysilanes and emphasizes the influence of the self-assembling behavior.     

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.     

Fluorescence emission control and switching of oxymethylcrowned spirobenzopyrans by metal ion

Oxymethylcrowned spirobenzopyran 1 and pyrenylspirobenzopyran 2 were synthesized, and fluorescence emission of their corresponding merocyanine form was examined in the presence of metal ions. For 2, fluorescence emission derived from the pyrene moiety was completely quenched by photoinduced electron transfer (PET) of the nitrogen atom when the merocyanine form was not produced, namely, without metal ions. However, when 2 was converted to the merocyanine form by the complexation of its crown ether with a metal ion, fluorescence resonance energy transfer (FRET) from the pyrene to the merocyanine moieties took place to produce fluorescence emission. This result demonstrates that the spirobenzopyran isomerization can function as a fluorescence emission switch. Fluorescence quantum yield measurement for 1 and 2 showed that fluorescence emission depends on the binding metal ion in which the fluorescence quantum yield generally increased with the increase of metal ion radius.     

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.     

Exciplex fluorescence as a diagnostic probe of structure in coordination polymers of Zn2+ and 4,4'-bipyridine containing intercalated pyrene and enclathrated aromatic solvent guests

Coordination polymers based on Zn(II)-4,4'-bipyridine (Zn-bipy) frameworks containing pyrene intercalated between adjacent layers and aromatic solvent molecules enclathrated within the framework cavities have been prepared and characterized for the first time. These compounds are highly fluorescent, and show broad, featureless emission spectra significantly red-shifted relative to pyrene monomer fluorescence; this has been assigned to pyrene-bipy exciplex emission. Single-crystal X-ray structural analysis shows that the presence of the aromatic solvent molecule within the cavities has a profound effect on the architecture of these frameworks: in the case of benzene, toluene, p-xylene, and chlorobenzene, the Zn-bipy framework consists of 1-D ladders, whereas in the case of o-dichlorobenzene (the largest solvent guest), the framework was based on a 2-D square grid. This difference in stoichiometry and architecture was also reflected in significant differences in the fluorescence of these coordination polymers, with three of the four compounds with 1-D ladder geometries having similar fluorescence maxima (ca. 520 nm) and lifetimes (ca. 70 ns), whereas the compound with square grid topology had a significantly blue-shifted maximum (ca. 460 nm) and shorter lifetime (ca. 42 ns). It is proposed that exciplexes form upon excitation of ground-state complexes, involving face-to-face bipy/pyrene complexes (pi-pi stacking interactions) in the case of the 1-D ladder structures, but edge-to-face bipy/pyrene and pyrene/o-dichlorobenzene complexes (C-H...pi interactions) in the case of the 2-D square grid structure.     

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.     

荧光探针法研究壳聚糖水凝胶形成过程及其性能

基于芘(Py)单体荧光光谱结构对微观环境变化的敏感性,以及介质粘度及Py分子间距对Py激基络缔合物形成的影响,以戊二醛交联壳聚糖(CS)水凝胶体系为例研究了Py荧光探针法监测水凝胶形成过程及其溶胀性能的可行性。结果表明,Py荧光光谱精细结构的变化(以I~3/I~1为参量)或Py激基缔合物荧光强度与单体荧光强度之比(I~E/I~M)的变化与CS水凝胶的形成及溶胀程度有很好的对应关系。此外,CS凝胶网状结构中包埋的聚N-异丙基丙烯酰胺(PNIPAM)的构象变化也可由探针光谱变化反映出来。利用这种荧光探针方法有助于从分子水平上探知凝胶形成过程的微观本质。此外,这种方法也可作为光纤传导监测凝胶形成过程和溶胀的基础。     

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.     

A Selective Cucurbit[8]uril-Peptide Beacon Ensemble for the Ratiometric Fluorescence Detection of Peptides

A convenient supramolecular strategy for constructing a ratiometric fluorescent chemosensing ensemble, consisting of a macrocyclic host (cucurbit[8]uril CB[8]), and a pyrene-tagged amphiphilic peptide beacon (AP 1), is reported. AP 1 unfolds upon encapsulation of the pyrene termini into the hydrophobic CB[8] cavity. This changes pyrene excimer to monomer emission. Substrates with higher affinity for the CB[8] cavity can displace AP 1 from the ensemble. The released AP 1 folds again to form a pyrene excimer, which allows for the ratiometric fluorescence monitoring of the substrate. In this report, the ensemble capacity for ratiometric fluorescence monitoring of biological substrates, such as amino acid derivatives, specific peptides, and proteins, in aqueous media is demonstrated.     

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.     

Membrane association and contact formation by a synthetic analogue of polymyxin B and its fluorescent derivatives

sP-B is a synthetic analogue of the natural lipopeptide antibiotic polymyxin B (PxB) that maintains the ability of the parent compound to form vesicle-vesicle contacts and induce lipid exchange. Exchange is selective, and only monoanionic phospholipids such as 1-palmitoyl-2-oleoyl-glycero-sn-3-phosphoglycerol (POPG) are transferred, whereas dianionic phospholipids such as 1-palmitoyl-2-oleoyl-glycero-sn-3-phosphate (POPA) are not, as shown by fluorescence experiments based on the excimer/monomer ratio of pyrene-labeled phospholipids. Synthetic fluorescent analogues of sP-B are used to investigate the peptide position and orientation in the intermembrane contacts: sP-Bw, an analogue that contains D-tryptophan (D-Trp) instead of the naturally occurring D-phenylalanine, and sP-Bpy, incorporating a pyrene group at the N-terminus. Tryptophan fluorescence, anisotropy, and quenching measurements performed with sP-Bw indicate that the peptide binds and inserts in anionic vesicles of POPG and POPA. However, significant differences are seen depending on the lipid composition, as also demonstrated by fluorescence resonance energy transfer (FRET) experiments from Trp to 7-nitro-2-1,3-benzoxadiazol (NBD) groups at the interface. Intermolecular FRET using sP-Bw as the donor and sP-Bpy as the acceptor indicates self-association of the peptide, possibly forming dimers, when bound to POPG vesicles at concentrations that induce the vesicle-vesicle contacts.     

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.     

Bifunctional fluorescent calix[4]arene chemosensor for both a cation and an anion

[reaction: see text] 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 Pb(2+) and Co(2+) 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.     

A dual role of phenylboronic acid as a receptor for carbohydrates as well as a quencher for neighboring pyrene fluorophore

A simple amino acid based compound (1) containing a phenyl boronic group and pyrene fluorophore showed an enhanced fluorescence in aqueous solutions at physiological pH through suppression of the photoinduced electron transfer from pyrene to boronic acid on carbohydrate binding. The compound exhibited an interesting fluorescence change depending on pH with decreased emission intensity at acidic pH but enhanced emission intensity at basic pH unlike the fluorescent carbohydrate chemosensors using a PET process with amine and aryl-boronic acid. We have characterized a dual role of phenylboronic acid as a receptor for carbohydrates as well as a quencher for the fluorescence of pyrene fluorophore.     

Fluorescence resonance energy transfer in polydiacetylene liposomes

Conjugated polydiacetylene (PDA) possessing stimuli-responsive properties has been intensively investigated for developing efficient sensors. We report here fluorescence resonance energy transfer (FRET) in liposomes synthesized using different molar ratios of dansyl-tagged diacetylene and diacetylene-carboxylic acid monomers. Photopolymerization of diacetylene resulted in cross-linked PDA liposomes. We used steady-state electronic absorption, emission, and fluorescence anisotropy (FA) analysis to characterize the thermal-induced FRET between dansyl fluorophores (donor) and PDA (acceptor). We found that the monomer ratio of acceptor to donor ( R ad) and length of linkers (functional part that connects dansyl fluorophores to the diacetylene group in the monomer) strongly affected FRET. For R ad = 10 000, the acceptor emission intensity was amplified by more than 18 times when the liposome solution was heated from 298 to 338 K. A decrease in R ad resulted in diminished acceptor emission amplification. This was primarily attributed to lower FRET efficiency between donors and acceptors and a higher background signal. We also found that the FRET amplification of PDA emissions after heating the solution was much higher when dansyl was linked to diacetylene through longer and flexible linkers than through shorter linkers. We attributed this to insertion of dansyl in the bilayer of the liposomes, which led to an increased dansyl quantum yield and a higher interaction of multiple acceptors with limited available donors. This was not the case for shorter and more rigid linkers where PDA amplification was much smaller. The present studies aim at enhancing our understanding of FRET between fluorophores and PDA-based conjugated liposomes. Furthermore, receptor tagged onto PDA liposomes can interact with ligands present on proteins, enzymes, and cells, which will produce emission sensing signal. Therefore, using the present approach, there exist opportunities for designing FRET-based highly sensitive and selective chemical and biochemical sensors.     

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。     

FRET-derived ratiometric fluorescence sensor for Cu

New N-(pyrenylmethyl)naphtho-azacrown-5 (1) was synthesized as an ‘On-Off’ fluorescent chemosensor for Cu²⁺. Excited at 240 nm corresponding to the absorption of naphthalene unit (energy donor) of 1, emission at 380 nm from pyrene unit (energy acceptor) is observed, indicating that intramolecular fluorescence resonance energy transfer (FRET-On) occurs in 1. When Cu²⁺ is added to a solution of 1, however, the fluorescence of pyrene is strongly quenched (FRET-Off) whereas that of naphthalene group is revived. Such FRET ‘On-Off’ behavior of 1 is observed only in the case of Cu²⁺ binding, but not for other metal cations. The high selectivity of 1 toward Cu²⁺ can be potentially applied to a new kind of FRET-based chemosensor. The FRET On-Off behavior is supported by computational studies. The calculated molecular orbitals of HOMO and LUMOs suggest the excited-state interactions leading to FRET from naphthalene to pyrene in 1, but no electron density changes in 1·Cu²⁺ complex.     

荧光探针法研究核壳结构有机硅-丙烯酸酯乳液的聚合行为

以芘为荧光探针,探讨了有机硅-丙烯酸酯核壳乳液聚合过程中,芘的第一振动峰(373 nm处)与第三振动峰(384 nm处)荧光强度的比值I1/I3与乳化剂、有机硅单体(D4)和引发剂(KPS)用量之间的关系,并结合聚合过程中探针芘的I1/I3峰值与单体转化率及乳胶粒形态演变之间的关系,研究了核壳结构有机硅-丙烯酸酯乳液的聚合行为.研究结果表明,探针芘的I1/I3峰值随乳化剂用量,D4用量,KPS用量不同发生相应的变化,随单体转化率的增加而增大.当乳化剂用量、D4用量、KPS与总单体的质量比依次为2 g、8 g、0.7%时,得到的乳液具有优良的综合性能.聚合反应过程中,当种子乳胶粒转变为核壳乳胶粒时,芘的I1/I3峰值仍呈现出明显的转变,说明有机硅-丙烯酸酯核壳乳液具有互穿聚合物网络结构.因此,荧光探针可用于研究有机硅-丙烯酸酯核壳乳液聚合反应进程.     

Electrogenerated chemiluminescence. Effect of a magnetic field on the delayed fluorescence and ECL of several systems involving excimers or exciplexes

The use of magnetic field effects in delayed fluorescence (DF) and electrogenerated chemiluminescence (ECL) studies to obtain information about the involvement of triplet state species in reactions leading to the production of monomeric and dimeric (excimer or exciplex) excited states is described. In the room temperature DF of pyrene and 1,2-benzanthracene, identical field effects are observed for monomer and excimer emission, in agreement with a mechanism involving a common intermediate produced on triplet-triplet annihilation (TTA), and different than previous DF results for 1,2-benzanthracene solutions at low temperatures. The ECL of the pyrene/N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) system also shows monomer and excimer emissions identically affected by magnetic field and in agreement with an ECL mechanism involving TTA. In the ECL of the S-methylanthracene (MA)/tri-p-tolylamine (TPTA) system, a field effect is observed for both the ¹MA^* and longer wavelength emission. In this case, however, a smaller effect is observed for the longer wavelength emission. A mechanism based on TTA to form ¹MA^* and some direct formation of exciplex on electron transfer is proposed.