Pyrene Excimer Emission Research Articles

In situ monitoring of polymeric patchy micelles upon non-covalent post-assembly modification

ABSTRACT Polymeric patchy micelles (PPMs) are nanostructures with distinct regions on their surfaces, offering unique properties for various applications. Herein, we present a straightforward method for monitoring the structure of PPMs formed via non-covalent post-assembly modification (NCPAM). By employing 1-pyrenemethylamine, a pyrene-based molecule, as both a modifier and fluorescent probe, we demonstrate that the formation of PPMs with a higher order aggregation state of pyrene induces a stronger pyrene excimer emission. This leads to variations in the excimer-to-monomer emission ratio, serving as a parameter for studying structural changes in PPMs during NCPAM. In situ monitoring of PPM formation and temperature-dependent transformations is achieved using fluorescent analytical method, providing valuable insights into their structural evolution and dynamic behaviour. This study offers a straightforward approach to understanding and controlling PPM structures, facilitating the design of advanced nanomaterials for diverse applications.

Investigation of silica particle growth by incorporation of a pyrene fluorescent probe

The growth of silica particles synthesized by the Stöber method was investigated by the co-condensation of pyrene sulfonyl chloride (PySCl) coupled to (3-aminopropyl)triethoxysilane (APTES). Growth by monomer addition could be distinguished from growth by aggregation based on the intensity of the pyrene excimer emission of the resulting particles. The influence of the base concentration, water/ethanol ratio, solvent, temperature, and type of silica precursor was studied. At high hydrolysis rates, the growth occurred primarily by aggregation, whereas growth by monomer addition was predominant at low hydrolysis rates. The results were confirmed by evaluating the accessibility of the co-condensed pyrene moieties and by determining the porosity of the particles.

Engineering circularly polarized light emission in nanostructured oligodimethylsiloxane-helicene chiral materials.

Chiroptical properties in the bulk state can be tuned by controlling the formation of chiral ordered nanostructures. Here, we present a series of discrete oligodimethylsiloxane-helicene-pyrene block molecules with varying oDMS lengths and study the nanostructures formed in both bulk and solution, including their chiroptical properties. In bulk, ordered 2D nanostructures self-assemble, driven by phase segregation induced by the siloxane oligomers, with clear differences in the properties of the racemic and enantiopure versions. Moreover, intermolecular pyrene interactions lead to excimer emission. As a result, up to a 5-fold increase in circularly polarized luminescence is observed in the solid state as compared to the solution, accompanied by a clear influence of the pyrene excimer emission on the overall emission process. Interestingly, in the ordered lamellar packing achieved from long oDMS units, the excimer emission shows very little net circular polarization, while in the disordered state achieved from shorter oDMS units, this excimer emission displays a significant degree of circular polarization. These results demonstrate that functionalizing chiroptical building blocks with discrete oligodimethylsiloxane chains is a versatile strategy to control photophysical properties and modulate chiroptical emission in bulk. This approach advances the integration of chiroptical materials into devices, enabling diverse applications ranging from optoelectronics to communication technologies.

Strong emission of excimers realized by dense packing of pyrenes in tailored bola-amphiphile nano assemblies

Pyrene is known for the quenched emission of excimers, especially in aqueous solution. Here, we report strong emission of pyrene excimers realized in amphiphile assemblies by controlling the face-to-face distance between the pyrene planes. We find that both the self-assembly behavior and emission properties of a cationic pyrene-containing amphiphile (denoted by PRB) are altered by exchanging the counterions. Upon the addition of sodium mesitylenesulfonate (Na MtS), the excimer emission of pyrene in self-assembled aggregates of PRB is greatly enhanced in aqueous solution. Concomitantly, the disk-like assemblies of PRB are converted to spherical particles, in which the repulsive interactions of the head groups are screened by replacing the counterions of the PRB molecules. The quantum yield of PRB increases from 0.5% to 16.6%, which is attributed to the dense packing of pyrene moieties in the aggregates. This study demonstrates that controlling supramolecular interactions is a feasible avenue to enhance the emission of pyrene excimers in amphiphile assemblies. The face-to-face distance between neighboring pyrenes is reduced The excimer emission of pyrene derivatives was boosted in the aggregated state The quantum yield increases by 2 orders of magnitude to >16% Pyrene is known for the quenched emission of excimers, especially in aqueous solution. Zhao et al. report the enhanced excimer emission of pyrene derivatives by controlling the intermolecular interactions in the aggregated state of assemblies, whereby the quantum yield increased by 2 orders of magnitude to >16%.

Measurements of viscosity profile in elastohydrodynamic lubrication film using fluorescence method under various contact pressure conditions

This paper describes rheological properties of hydrodynamic and elastohydrodynamic lubrication (EHL) film under various contact pressure conditions using the fluorescence measurement method. In this measurement method, the viscosity and the information about the state of the lubricant (liquid or solid) can be obtained via the analysis of fluorescence spectrum of a pyrene excimer emission. Previous research revealed that the intensity of excimer emission decreased with increasing of viscosity. In addition, the intensity ratio between the excimer peak and lubricant 5P4E fluorescence peak was introduced for the analysis, and the ratio decreased with increasing viscosity of lubricant. In this study, the viscosity profile obtained from the relationship between the intensity ratio and viscosity showed that the state of lubricant in the lubrication film corresponded almost exactly to the lubrication regime proposed in previous researches. It is concluded that the viscosity measurement technique proposed in this study is useful method for practical uses in hydrodynamic and elastohydrodynamic conditions, while in the high viscosity range, the measured viscosity varies widely due to the variation of intensity ratio.

Boronic Acid‐containing Stimuli‐responsive Polymers Modified Nanopores for Label‐free Dual‐signal‐output Detection of Glucose

AbstractHerein, a dual‐signal‐output glass nanopore system was developed for sensing glucose. Upon binding glucose, the boronic acid‐containing stimuli‐responsive polymer underwent a wettability switch and pKa shift. When the polymer was immobilized on the inner wall of nanopore, the nanopore offered a sensitive method for evaluating glucose by ion rectification. Besides, due to the electrostatic assembly of cationic pyrene onto the glucose‐bound anionic polymer, the pyrene excimer emission was observed. By separating the substrate binding and fluorescence reporting process, this work avoided the fluorescence labeling of the target and nanopore, thus simplifying the design of dual‐signal‐output nanopore for potential point‐of‐care test.

Synthesis and Photophysical Properties of Light-Harvesting Gold Nanoclusters Fully Functionalized with Antenna Chromophores.

The development of efficient light-harvesting systems is important to understand the key aspects of solar-energy conversion processes and to utilize them in various photonic applications. Here, atomically well-defined gold nanoclusters are reported as a new platform to fabricate artificial light-harvesting systems. An efficient amide coupling method is developed to synthesize water-soluble Au22 clusters fully protected with pyrene chromophores by taking advantage of their facile phase-transfer reaction. The synthesized Au22 clusters with densely packed 18 pyrene chromophores (Au22 -PyB18 ) exhibit triple-emission in blue, green, and red wavelength regions arising respectively from pyrene monomer, pyrene excimer, and Au22 emission, producing bright white light emission together. The photoluminescence of Au22 is enhanced by more than tenfold, demonstrating that pyrenes at the periphery efficiently channel the absorbed energy to the luminescent Au22 at the center. A combination of femtosecond transient absorption and anisotropy measurements of Au22 -PyB18 explicitly reveals three main decay components of 220 fs, 3.5ps, and 160ps that can be assigned to energy migration between pyrenes and energy transfer processes from pyrene monomer and excimer to the central Au22 , respectively.

Fine-tuning of the optical output in a dual responsive catenane switch.

A [2]catenane switch where the intramolecular pyrene excimer emission can be controlled by orthogonal cation binding and solvent polarity change in various amplitudes and dynamic ranges is reported.

Diversiform Nanostructures Constructed from Tetraphenylethene and Pyrene-Based Acid/Base Controllable Molecular Switching Amphiphilic [2]Rotaxanes with Tunable Aggregation-Induced Static Excimers.

Dual-emissive tetraphenylethene (TPE) and pyrene-containing amphiphilic molecules are of great interest because they can be integrated to form stimuli responsive materials with various biological applications. Herein, we report the study of mechanically interlocked molecules (MIMs) with aggregation-induced static excimer emission (AISEE) property through a series of TPE and pyrene-based amphiphilic [2]rotaxanes, where t-butylcalix[4]arene with hydrophobic nature was used as the macrocycle. Evidently, by adorning TPE and pyrene units in [2]rotaxanes P1, P2, P1-b, and P2-b, they display remarkable emission bands in 70% of water fraction (fw) in tetrahydrofuran (THF)/water mixture, which could be attributed to the restricted intramolecular rotation of phenyl groups, whereas prominent blue-shifted excimer emission of pyrene started to appear as fw reached 80% for P1 and 90% for P1-b, P2, and P2-b, which was ascribed to the favorable π-π stacking and hydrophobic interactions of the pyrene rings that enabled their static excimer formation. The well-defined distinct amphiphilic nanostructures of [2]rotaxanes including hollowspheres, mesoporous nanostructures, spheres, and network linkages can be driven smoothly depending on the molecular structures and their aggregated states in THF/water mixture. These fascinating diversiform nanostructures were mainly controlled by the skillful manner of reversible molecular shuttling of t-butylcalix[4]arene macrocycle and also the interplay of multinoncovalent interactions. To further understand the aggregation capabilities of [2]rotaxanes, the human lung fibroblasts (MRC-5) living cell incubated with either P1, P2, P1-b, or P2-b was studied and monitored by confocal laser scanning microscopy. The AISEE property was achieved at an astonishing level by integrating TPE and pyrene to MIM-based reversible molecular switching [2]rotaxanes; furthermore, distinct nanostructures, especially hollowspheres and mesoporous nanostructures, were observed, which are rarely reported in the literature but are highly desirable for future applications.

A simple triazole-linked bispyrenyl-based xylofuranose derivative for selective and sensitive fluorometric detection of Cu2+

Triazole-linked xylofuranose derivatives having one pyrene or two pyrene moieties were synthesized and their fluorescence properties towards various cations and anions were investigated. Only, bis-triazoles appended bispyrenyl-based sugar derivative 1 exhibited selective and sensitive fluorescence quenching effect in the presence of Cu2+ ions over a wide range of cations and anions in acetonitrile. The ON-OFF type fluorescence response of 1 was explained by the conformational changes from strong excimer emission of pyrene to weak pyrene monomer emission due to an interaction between Cu2+ and inward-facing triazole groups. The limit of detection (LOD) of sensor 1 for Cu2+ was found to be 0.15 µM, which is well accepted as per WHO’s guidelines.

Determination of association constants and FRET in hydrazide-based molecular duplex strands

The association constants for the hydrazide-based molecular duplex strands can be determined via monitoring the pyrene excimer emission. By mixing pyrene and perylene labelled oligomers, supramolecular substitution reactions induced efficient FRET.

Positive Identification of DNA Cleavage by CRISPR-Cas9 Using Pyrene Excimer Fluorescence to Detect a Subnanometer Structural Change.

The Cas9 nuclease binds and cleaves DNA through its large-scale structural rearrangements. However, its unique property of not releasing the cleaved DNA has forbidden spectroscopic detection of the cleavage event. Here, we employ a novel fluorescence probe based on pyrene excimer emission to detect a minute structural change not detectable by other methods and demonstrate its applicability to spectroscopic tracking of the Cas9 nuclease activity in time. We show that the intensity of excimer emission depends sensitively on a subtle change in the structural environment of the target nucleic acid, which enables discrimination between cleaved and uncleaved nucleic acids within the DNA/Cas9/gRNA ternary complex. Kinetic parameters were obtained from the temporal evolution of the excimer emission, which revealed that DNA binding is hardly affected by PAM-distal mismatches, whereas the rate of cleavage by Cas9 decreases dramatically even with a 1-bp mismatch. Spectroscopic studies using the pyrene-based probe should be promising for biomolecular systems affected by subnm structural changes.

Cyclodextrin supramolecular inclusion-enhanced pyrene excimer switching for highly selective detection of RNase H

Here, we report a novel fluorescence method for the highly selective and sensitive detection of RNase H by combining the use of a dual-pyrene-labeled DNA/RNA duplex with supramolecular inclusion-enhanced fluorescence. Initially, the probe is in the “off” state due to the rigidness of the double-stranded duplex, which separates the two pyrene units. In the presence of RNase H, the RNA strand of the DNA/RNA duplex will be hydrolyzed, and the DNA strand transforms into a hairpin structure, bringing close the two pyrene units which in turn enter the hydrophobic cavity of a γ-cyclodextrin. As a result, the pyrene excimer emission is greatly enhanced, thereby realizing the detection of RNase H activity. Under optimal conditions, RNase H detection can be achieved in the range from 0.08 to 4 U/mL, with a detection limit of 0.02 U/mL.

Rapid Identification of Bacteria by Membrane-Responsive Aggregation of a Pyrene Derivative.

An imidazolium-derived pyrene aggregation was developed to rapidly identify and quantify different bacteria species. When the nonemissive aggregates bound to the anionic bacteria surface, the sensor disassembled to turn on significant fluorescence. At the same time, ratiometric signals between pyrene monomer and excimer emission were controlled by different interactions with various bacteria surfaces. The resulted different fluorescent emission profiles then were obtained as fingerprints for various bacterial species. By converting emission profiles directly into output signals of two channels, fluorescence increase and ratiometric change, a two-dimensional analysis map was generated for bacteria identification. We demonstrated that our sensor rapidly identified 10 species of bacteria and 14 clinical isolated multidrug-resistant bacteria, and we determined their staining properties (Gram-positive or Gram-negative).

Monitoring the confinement of methylene blue in pyrene labeled poly(acrylic acid)

This work was devoted to investigate the aggregation of methylene blue (MB) with pyrene labeled poly(acrylic acid) (PAA25Py3) by using the measurements of UV–vis absorption, steady-state and time-resolved fluorescence. For comparison, the effect of unlabeled poly(acrylic acid) (PAA25) on the self-association of MB was also evaluated. The spectral positions of the absorption and emission bands of MB as well as the pyrene monomer and excimer emissions were used to assess the local changes of polymer/MB microenvironment. The binding mechanism and thermodynamic analysis for the interaction between MB and pyrene labeled poly(acrylic acid) were evaluated by fluorescence quenching measurements. Moreover, the strategy of switching of pyrene excimer/monomer emission was used to manage the self-aggregation of the pH-responsive fluorescent polymer with phenothiazinium dye. The UV–vis absorption and fluorescence results showed that low amounts of polymers provoked the self-association of MB. At high concentrations of polymer, the MB monomer is stabilized. The labeling of polymer with pyrene induced a dramatic changing of optical properties suggesting that a peculiar process occurred between PAA25Py3 and MB. At low quencher concentrations, both steady-state and time-resolved fluorescence data indicated a static quenching process. The thermodynamic parameters (∆H, ∆S and ∆G) and the efficiency of pyrene excimer formation revealed that the association of MB with the fluorescent polymer occurred spontaneously due to non-covalent hetero π-π stacking, hydrophobic and electrostatic interactions. The study highlights the key contribution of the π-π stacking interactions in the capturing of methylene blue in pyrene labeled poly(acrylic acid). The outcome may be useful in biomedical applications or in wastewater treatment.

Amplified polarization properties of electrospun nanofibers containing fluorescent dyes and helical polymer.

Nanofibers with the cationic fluorescent molecules, 1-pyrenemethylamine hydrochloride (PyrMA) and α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphyrin p-toluenesulfonate (TMPyP), in the presence of complementary anionic chiral polysaccharide, hyaluronic acid (HA) and transparent polymer, polyethylene oxide (PEO) were successfully prepared using an electrospinning technique. The results showed that the fluorescence spectra of electrospun nanofibers (ENFs) of PEO-HA-PyrMA exhibit a higher amount of pyrene excimer emission when the [PyrMA]/[HA] ratio was increased from 0.5 to 1, while the concentration of TMPyP had no remarkable effect on the fluorescence of the PEO-HA-TMPyP ENFs. From circular dichroism (CD) characterization, the ENFs of both dyes exhibit stronger intensities in the apparent CD spectra upon increasing the dye ratio. Moreover, they also showed higher CD intensities when compared with those of solutions and thin films prepared using other methods. The apparent CD in this work was proved to mainly originate from linear dichroism (LD) and linear birefringence (LB) obtained by macroscopic alignment along the electrospinning process. These results suggest the advantages of molecular orientation via electrospinning, together with chirality induction by incorporation of a chiral HA polymer. The enhancement of these polarization properties provides great possibilities for improving fluorescent-chiral nanofibers for further optoelectronic applications.

Filamentous Virus Oriented Pyrene Excimer Emission and Its Efficient Energy Transfer

We present here that pyrene derivative can be arranged in close proximity using M13 virus as framework through click reaction. The observation of excimer emissions of pyrene was a direct evidence for the proper spatial arrangements of chromophores in the architecture, in which both ground-state and excited-state electronic interactions of pyrenes were facilitated. Efficient energy transfer could be induced through the electrostatic interactions between the M13 backbone and the positively charged rhodamine 6G. The investigation of chromophore-modified M13 and its energy transfer process would be beneficial for exploiting the structures of various natural virus and artificially self-assembled virus-like particles.

Reaction-Driven Self-Assembled Micellar Nanoprobes for Ratiometric Fluorescence Detection of CS2 with High Selectivity and Sensitivity.

The detection of highly toxic CS2, which is known as a notorious occupational hazard in various industrial processes, is important from both environmental and public safety perspectives. We describe here a robust type of chemical-reaction-based supramolecular fluorescent nanoprobes for ratiometric determination of CS2 with high selectivity and sensitivity in water medium. The micellar nanoprobes self-assemble from amphiphilic pyrene-modified hyperbranched polyethylenimine (Py-HPEI) polymers with intense pyrene excimer emission. Selective sensing is based on a CS2-specific reaction with hydrophilic amino groups to produce hydrophobic dithiocarbamate moieties, which can strongly quench the pyrene excimer emission via a known photoinduced electron transfer (PET) mechanism. Therefore, the developed micellar nanoprobes are free of the H2S interference problem often encountered in the widely used colorimetric assays and proved to show high selectivity over many potentially competing chemical species. Importantly, the developed approach is capable of CS2 sensing even in complex tap and river water samples. In addition, in view of the modular design principle of these powerful micellar nanoprobes, the sensing strategy used here is expected to be applicable to the development of various sensory systems for other environmentally important guest species.

Pseudopeptidic fluorescent on-off pH sensor based on pyrene excimer emission: Imaging of acidic cellular organelles

A pseudopeptidic compound comprising a central C2 symmetric bis(aminoamide) moiety derived from the amino acid serine and two pyrene groups at the ends, Et(SerPyr)2, has been efficiently prepared. In aqueous solution, it displays fluorescence bands typical of both monomer and excimer pyrene emission. In particular, the emission at 490nm, due to the excimer, is strongly pH-dependent, with a linear 4.7-fold increase from pH 6.0 to pH 4.2. This feature makes Et(SerPyr)2 suitable for intracellular pH sensing in the acidic range. A fluorescence microscopy study revealed that Et(SerPyr)2 allows the visualization of acidic organelles in human lung adenocarcinoma A549 cells, as well as their pH changes over time. Other advantages of this probe include its easy and modular synthesis, good photostability, high quantum yield, fast optical response, large Stokes shift (ca. 145nm) and low cytotoxicity.

Fluorescence reporting of G-quadruplex structures and modulating their DNAzyme activity using polyethylenimine-pyrene conjugate.

Four-stranded G-quadruplex structure is one of the most important non-canonical secondary structures of DNA formed by guanine (G)-rich sequences. G-rich DNA sequences are known to occur in the human genome, especially in the telomere 3' end and in oncogene promoters such as c-MYC and c-KIT. In this context, we designed pyrene-conjugated polyethylenimine (PEI-Py) as a fluorescence reporter for the recognition and detection of G-quadruplex structures of G-rich deoxyoligonucleotides and human telomere and gene promoter sequences, under ambient conditions. PEI-Py exhibited prominent pyrene excimer emission in the presence of G-quadruplex structures of G-rich deoxyoligonucleotides and biologically relevant DNA sequences. PEI-Py further displayed the modulation of DNAzyme activity of various G-quadruplex structures in the presence of hemin and hydrogen peroxide.