Aggregation-induced Fluorescence Research Articles

A novel carbazole derivative containing fluorobenzene unit: aggregation-induced fluorescence emission, polymorphism, mechanochromism and non-reversible thermo-stimulus fluorescence

Different conformations and packing modes induce the compound with unique stimuli-responsive properties.

Branched triphenylamine luminophores: Aggregation-induced fluorescence emission, and tunable near-infrared solid-state fluorescence characteristics via external mechanical stimuli

Three AIE-active branched luminophores (defined as 4a, 4b and 4c) containing triphenylamine and carbazole units forming intramolecular charge transfer (ICT) states have been developed. The studies of the mechanical stimuli effect on solid state showed that the branch number can affect effectively the performance of the tunable fluorescence in the solid state. Interestingly, only compound 4a displayed a distinct bathochromic shift of its fluorescence emission from the visible (λem = 598 nm) to the near-infrared section (λem = 643 nm) by mechanical stimuli. Moreover, 4a exhibited an obvious crystallization-induced emission enhancement (CIEE) effect. The crystal samples of 4a emit strong orange light with 49.8% solid-state fluorescence quantum yield (ФF) and the amorphous showed decreased red emission with 7.6% (ФF). Mechanical grinding and organic solvent stimuli can reversibly change the phase transition between crystalline and amorphous states. However, compounds 4b and 4c are not sensitive to the mechanical stimuli, because it is difficult for them to form crystalline structure due to bigger steric hindrance effect. The mechanism for their solid-state fluorescence behavior was investigated in detail by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analysis.

Aggregation-Induced Fluorescence Probe for Monitoring Membrane Potential Changes in Mitochondria.

Fluorescent probe 2 was designed for selectively determining mitochondria membrane potential changes. The probe selectively detects changes in the mitochondria membrane potential in a manner that is more sensitive than that of the commercially available indicator, Rodamine 123. As a result, the probe 2 is ideal for future studies designed to assess the functions of mitochondria in cells.

Inositol directed facile “green” synthesis of fluorescent gold nanoclusters as selective and sensitive detecting probes of ferric ions

In this paper, we developed one-pot facile synthetic approach for preparing fluorescent gold nanoclusters (AuNCs) by utilizing reducing-cum-stabilizing inositol (INOS). The as-prepared INOS protected gold nanoclusters (INOS@AuNCs) have excellent monodispersity with uniform size <2.0nm and exhibit strong inherent fluorescence at 470nm with a decay time of 12.01ns. Interestingly, ferric ions (Fe3+) can significantly quench the fluorescence of the synthesized INOS@AuNCs leading to the efficient Fe3+ sensing. On the basis of results obtained from high-resolution transmission electron microscopy (HRTEM), an aggregation-induced fluorescence quenching mechanism was proposed. Based on these fascinating findings, a facile, fast, “green” and highly sensitive AuNCs-dependant fluorescent sensor probe was developed to detect Fe3+ ions in water resources and Over-The-Counter (OTC) medicines. Stern-Volmer plot showed a good linear calibration curve for Fe3+ assay in the range of 1.0–1000μM (R2=0.996) and good precision response to 100.0μM Fe3+ with RSD of 2.94% (n=3) was also achieved. The obtained limit of detection of 0.54μM for the determination of Fe3+ ions is 10 times lower than the limit value (≈5.5μM) allowed by the U.S. Environmental Protection Agency in drinkable water, indicating the sensitivity of the fluorescent probe of Fe3+ sensing. The excellent selectivity obtained among 16 types of metal ions underpins INOS@AuNCs as a promising sensor for real time detection of Fe3+ in environmental water samples and pharmaceutical tablets.

Tuning aggregation-induced emission properties with the number of cyano and ester groups in the same dibenzo[b,d]thiophene skeleton for effective detection of explosives

Three aggregation-induced emission (AIE) active molecules were designed and synthesized where they have the same dibenzo[b,d]thiophene skeleton but the different number of cyano and ester groups. Aggregation-induced fluorescence experiments reveal that compounds 1–3 show a remarkable bathochromic-shift and AIE phenomenon. With the enhancement of water volume fractions, the intensity of emission band presents a step-by-step increase when fw=0–70% in compound 1, where the maximum emission wavelength is 564nm in the aggregated state and the peak area when fw=90% is 5-fold more than that when fw=0%. Furthermore, fluorescence titration results demonstate that this family of dibenzothiophene derivatives 1–3 is one of potential selective chemosensors for picric acid in aqueous phase and the obvious color change of the cellulose-based dibenzothiophene mixtures is illustrated with the addition of different explosives. In addition, theoretic computational studies on related luminogens have been carried out. To the best of our knowledge, this is the first fabrication of cellulose-based dibenzothiophene composites exhibiting AIE properties for effective detection of explosives.

Histone controlled aggregation of tetraphenylethene probe: A new method for the detection of protease activity

A novel fluorescence “turn-on” assay for protease activity based on controlled aggregation of a tetraphenylethene probe is reported. A tetraphenylethene derivative (TPE-2+) with two positive charges is used in this study. TPE-2+ has no emission in an aqueous solution. Heparin is an anionic polymer, which can induce aggregation of TPE-2+. Strong aggregation-induced fluorescence emission (AIE) is observed. Histone is a cationic protein, it binds with heparin via electrostatic attractive interactions, which hinders the binding of TPE-2+ to heparin. TPE-2+ is released, and a decreased emission signal is detected. Upon the addition of a protease, histone is hydrolyzed into small fragments, which weakens its competitive binding to heparin. Free heparin induces aggregation of TPE-2+. A turn-on emission signal is recorded. An efficient and convenient fluorescence assay for protease activity is therefore established.

Cover Feature: Aromatic Thioethers as Novel Luminophores with Aggregation‐Induced Fluorescence and Phosphorescence (Chem. Eur. J. 55/2017)

Cover Feature: Aromatic Thioethers as Novel Luminophores with Aggregation‐Induced Fluorescence and Phosphorescence (Chem. Eur. J. 55/2017)

Synthesis, aggregation-induced emission and application as chemosensor for explosives of a 1,10-phenanthroline derivative and its rhenium(I) carbonyl complex having triphenylamino and thienyl donors

A C-shaped 1,10-phenanthroline ligand and its rhenium(I) carbonyl complex were designed and synthesized. Single-crystal structure reveals that one chloroform molecule is accommodated on this ligand and the bond lengths of double hydrogen bonding interactions is 2.31 and 2.67Å, respectively, between two nitrogen atom sites of 1,10-phenanthroline and one hydrogen atom of chloroform. Aggregation-induced fluorescence experiments demonstrate that the ligand presents an aggregation-induced emission enhancement from 60% to 70% water volume fractions, while the complex shows a red-shifted aggregation-caused quenching phenomenon from 461 to 506nm. Furthermore, fluorescence titration analysis proves that the ligand is one of a potential chemosensors for 2-methyl-1,3-dinitrobenzene in tetrahydrofuran solution. In addition, theoretic computational studies on related ligand and complex have also been carried out.

L-Histidine-protected copper nanoparticles as a fluorescent probe for sensing ferric ions

Ferric ions (Fe3+) play an important role in various chemical and physiological functions. Thus, analytical methods for the detection of Fe3+ in the environment are highly in demand. In this work, a simple chemical reduction method for synthesizing water soluble l-histidine capped copper nanoparticles (l-His-CuNPs) was successfully established. l-Histidine and ascorbic acid were acted as the capping scaffold and reducing agent, respectively. The as-prepared l-His-CuNPs were characterized by fluorescence spectroscopy, ultraviolet-visible spectrophotometry, Fourier-transform infrared spectroscopy, and transmission electron microscopy. The l-His-CuNPs show maximum luminescence at 495nm when excited at 385nm. Based on an aggregation-induced fluorescence quenching (AIQ) mechanism, a sensitive and selective sensor for Fe3+ was developed. The detection limit (3s/slope) is 82nM and the linear range is from 0.10 to 20μM. Moreover, the developed sensor was successfully employed in the detection of Fe3+ in real water samples.

Red-Emissive Carbon Dots for Fingerprints Detection by Spray Method: Coffee Ring Effect and Unquenched Fluorescence in Drying Process.

Brightly red fluorescent carbon dots are synthesized hydrothermally and dissolved in diluted hydrochloric acid solution. Such carbon dots exhibit excitation-independent emission at about 620 nm with quantum yield over 10%, which is visible in daylight. After the carbon dots solution is sprayed to the fingerprints on various solid substrates and dried in air, clear fingerprints can be seen under an ultraviolet lamp and stay stable for 1 day. Detailed characterizations suggest that during the drying process, the coffee-ring effect and the electrostatic interactions between the carbon dots and the fingerprint residues prevent the typical aggregation-induced fluorescence quenching of carbon dots.

One-step synthesis of orange fluorescent copper nanoclusters for sensitive and selective sensing of Al3+ ions in food samples

One-step approach was developed for the fast synthesis of copper nanoclusters (CuNCs), which were used as a fluorescent probe for the sensitive detection of Al3+ in food samples. For this, aqueous CuSO4 was reduced into CuNCs by dithiothreitol (DTT) at room temperature within 30min. The synthetic process was fast, simple and easy. The DTT-capped CuNCs (DTT-CuNCs) were characterized by UV–vis absorption, fluorescence, FT-IR, TEM and XPS. The DTT-CuNCs display orange fluorescence with a maximum emission at 590nm while excitation at 360nm. The aggregation-induced fluorescence enhancement property of DTT-CuNCs in presence of Al3+ was found. On this basis, we developed a simple, sensitive, selective turn-on fluorescent sensor for the detection of Al3+ in food samples. Under the optimized conditions, the enhanced fluorescence intensity exhibited a good linear relationship with Al3+ concentrations in the range from 0.01μM to 7μM with a detection limit of 0.01μM. The DTT-CuNCs-based fluorescent probe has been successfully used to assay the content of aluminum in real food samples such as the fried food and pasta. These results demonstrate the great potential of the DTT-CuNCs-based fluorescence sensor for the routine estimation of Al3+ content in food samples.

Redox-modulated near-infrared electrochromism, electroluminochromism, and aggregation-induced fluorescence change in an indolo[3,2-b]carbazole-bridged diamine system

A new indolo[3,2-b]carbazole-based compound (1) has been developed by linking two redox-active diphenylamine moieties to the rigid π-conjugated indolo[3,2-b]carbazole core. Its first two completely reversible oxidation steps are mainly related to the two terminal amine centers, and a moderate electron coupling between these amine centers has been determined. The associated oxidized species 1+ and 12+ both exhibited strong NIR absorptions, and a completely reversible conversion among three different colors (light-yellow, red, and blue, corresponding to neutral, monocationic and dicationic states, respectively) could be realized. In addition, reversible switching between turn-off and turn-on of its fluorescence could be accomplished by electrochemical oxidation and reduction, respectively. Compound 1 also exhibited obvious fluorescence color changes during its aggregate-forming process, and its solid showed bright-yellow fluorescence with a high emission quantum yield of 30%.

A red-emissive oxadiazol-triphenylamine BODIPY dye: synthesis, aggregation-induced fluorescence enhancement and cell imaging

Abstract A novel red aggregation-induced emission enhancement (AIEE) chromophore named OPA-BODIPY was designed based on 2-[4-( tert -butyl)phenyl]-5-(4-ethenylphenyl)- 1,3,4-oxadiazole and triphenylamine-BODIPY structure. It was synthesized through a new approach utilizing palladium-catalysed Heck reaction. It exhibited deep-red emission in solid state with a wavelength of 614 nm. It had bimodal emission in THF centred at 647 nm and 513 nm, the quantum yield of OPA-BODIPY at 647 nm was 0.11 while that at 513 nm was 0.01. The emission intensity in 90% THF/water mixtures was the strongest and the peak value was about 50 times of that in 10% THF/water, thus OPA-BODIPY performed typical deep-red fluorescence enhancement. The fluorescence intensity of OPA-BODIPY was strengthened continuously with increasing concentration of bovine serum albumin (BSA) which showed OPA-BODIPY could function as bioprobe for BSA. It was applied to cell imaging and showed a good uptake by MDA-MB-231 cells which suggested its promising application for biosensors.

All-or-none switching of photon upconversion in self-assembled organogel systems.

Aggregation-induced photon upconversion (iPUC) based on a triplet-triplet annihilation (TTA) process is successfully developed via controlled self-assembly of donor-acceptor pairs in organogel nanoassemblies. Although segregation of donor from acceptor assemblies has been an outstanding problem in TTA-based UC and iPUC, we resolved this issue by modifying both the triplet donor and aggregation induced emission (AIE)-type acceptor with glutamate-based self-assembling moieties. These donors and acceptors co-assemble to form organogels without segregation. Interestingly, these donor-acceptor binary gels show upconversion at room temperature but the upconversion phenomena were lost upon dissolution of the gels on heating. The observed changes in TTA-UC emission were thermally reversible, reflecting the controlled assembly/disassembly of the binary molecular systems. The observed on/off ratio of UC emission was much higher than that of the aggregation-induced fluorescence of the acceptor, which highlights the important role of iPUC, i.e., multi-exciton TTA for photoluminescence switching. This work bridges iPUC and supramolecular chemistry and provides a new strategy for designing stimuli-responsive upconversion systems.

A smart organic gel template as metal cation and inorganic anion sensor.

A carboxamide based molecule has shown unique gelation property in an aqueous mixture of DMF or DMSO. The gel itself has shown aggregation-induced fluorescence enhanced emission (AIEE), which can be utilized effectively in sensing ferrous and ferric ions as both of them switch off the fluorescence completely. An investigation by IR spectroscopy reveals an enhanced π interaction of nitrile group with the iron center and this could be the possible reason behind the complete quenching of AIEE. This molecule was further investigated for the formation of metallogels for a wide array of cations, which in turn can act in tandem to behave as a dynamic array to detect several anions by either switching off or switching on the emission property of the metallogels.

Highly fluorescent au nanoclusters: Electrostatically induced phase transfer synthesis for Cu2+ sensing.

This paper reports a convenient method for the synthesis of highly fluorescent Au nanoclusters (NCs) via electrostatically induced phase transfer. Furthermore, on the basis of an aggregation-induced fluorescence quenching mechanism, the potential application for Cu2+ sensing on the fluorescence emission of the Au NCs is discussed. These prepared fluorescent Au NCs offer acceptable sensitivity, high selectivity, and a limit of quantitation of 0.02μM for the measurement of Cu2+ , which is lower than the maximum level (1ppm, equals to 15.6μM) of Cu2+ permitted in drinking water in China. This study contributes to the further development of practical applications with fluorescent NCs.

Polyhedral-oligosilsesquioxane containing poly(methyl methacrylate) perylenebisimide microspheres with high solid state emission

A series of novel fluorescent poly(methyl methacrylate) microbeads with narrow size distribution and intense solid state emission were designed and prepared by dispersion polymerization. The featured polyhedral oligosilsesquioxane was introduced into the perylene bisimides fluorophore system to fabricate polymeric microspheres. With poly (12-hydroxystearic acid) chains grafted to poly(methyl methacrylate) backbone as stabilizer, the obtained microspheres were narrow distributed as well as easily dispersed which are shown in the dynamic light scattering and scanning electron microscope measurement. Fluorescence microscope images of petroleum-ether dispersion of the sample exhibited strong orange emission with stability against photobleaching. More importantly, due to the steric hindrance of bulky polyhedral oligosilsesquioxane moieties, the aggregation-induced fluorescence quenching of perylene bisimides can be suppressed significantly, thus the solid-state quantum yield of the microspheres can be boosted to 68%, which is the highest record for perylene bisimide along polymeric microspheres. The excellent luminescent property, in combination with the monodisperse nature and the high stability against photobleaching of the polyhedral-oligosilsesquioxane containing microspheres, makes them a kind of promising material for fabrication of luminescent devices.

Facile preparation of fluorescent Au nanoclusters-based test papers for recyclable detection of Hg2+ and Pb2+

A simple, portable and recyclable method has been developed for on-site and real-time detection of Hg2+ and Pb2+ by naked eyes by using Au nanoclusters-based test paper as the fluorescent sensor. The high specificity of Hg2+ and Pb2+ to Au nanoclusters provided excellent selectivity over 15 kinds of other ions. Interestingly, an apparent fluorescent quenching of the test paper was shown when exposed to Hg2+, while a significant fluorescent enhancement was observed in the presence of Pb2+, which could be attributed to aggregation-induced fluorescence quenching and enhancement. The limit of detection for Hg2+ and Pb2+ by naked eyes was 5μM and 50μM, respectively. More importantly, the cyclic utilization of the test paper was achieved by immersing the test papers into ethylenediamine tetraacetic acid to recover the fluorescence of the test paper, which contributed to reducing resource consumption. Otherwise, the GSH-AuNCs test paper was competent for a practical application in environmental water samples with strong anti-interference ability.

Pyrophosphate Sensor Based on Principal Component Analysis of Conjugated Polyelectrolyte Fluorescence.

The pyrophosphate anion (PPi) plays an important role in biochemical processes. Therefore, a simple but reliable analytical technique is essential for selective detection of PPi in biochemical systems. Here, we present a principal component analysis (PCA) method for analytical determination of PPi concentration using a fluorescent conjugated polyelectrolyte (CPE) combined with a polyamine modifier. The CPE has anionic side chains and dissolves molecularly in water, as indicated by its structured fluorescence emission spectrum. However, addition of tris(3-aminoethyl)amine (tetraamine or N4) quenches the CPE fluorescence emission. Tetraamine, which is a polycation at neutral pH, binds multiple anionic CPE chains, leading to aggregate formation, resulting in aggregation-induced fluorescence quenching. Addition of PPi to the polymer–amine aggregate reverses the process, resulting in fluorescence recovery. The relatively higher concentration of PPi compared to that of the polymer allows it to effectively compete to bind the amine, thus releasing molecularly dissolved polymer chains. Fluorescence correlation spectroscopy of the P1/N4 complex and of P1/N4/PPi confirms the change in size of the CPE aggregates that occurs upon reversible aggregation. Application of PCA to the fluorescence emission data set of standard samples yields two principal components, which are used to create a predictive model for PPi analysis. The PCA method is able to directly determine the concentration of PPi with approximately 95% accuracy within the concentration range from 100 μM to 3 mM, without the need for a reference state as is typically needed for ratiometric fluorescence assays.

Preparation, properties and applications in cell imaging and ions detection of conjugated polymer nanoparticles with alcoxyl bonding fluorene core

A novel conjugated polymer (PFP) comprised of fluorene, benzene and alcoxyl units was synthesized by a Suzuki coupling reaction between fluorene borate and dibromobenzene derivant. Due to its longer alcoxyl groups in the side chain, PFP polymer possesses good solubility in common organic solvents. Accordingly, conjugated polymer nanoparticles (CPNs) from PFP polymer were easily prepared by a re-precipitation method. A spherical structure of the CPNs with an average diameter of ~75nm was verified by dynamic light scattering (DLS) and scanning electron microscopy (SEM). The CPNs exhibit high photostability, good biocompatibility and low cytotoxicity. Based on these excellent properties, the CPNs as staining and labeling regents were used to cell imaging and located in the cytoplasm. Interestingly, the fluorescent probe based on CPNs displays high selectivity and sensitivity for Fe(III) in water because of the aggregation-induced fluorescence quenching action between CPNs and Fe(III). The contribution of the report lies in providing a new strategy for designing and developing CPNs-based probes, and applying in the interdisciplinary fields of chemistry, biology and material sciences.