A Fluorescent Probe for Hg2+ Based on Gold(I) Complex with An Aggregation‐Induced Emission Feature

A gold(I) complex that exhibited aggregation‐induced emission in acetonitrile‐water mixtures was designed. It showed high selectivity and sensitivity for Hg²⁺ in acetonitrile‐H₂O (1:1, V:V) solution. Dynamic light scattering measurements were conducted to verify that the addition of Hg²⁺ changed the particle size and induced fluorescence quenching.     

A novel Hg2+ fluorescence sensor TPE-TSC based on aggregation-induced emission

Abstract

A fluorescent sensor TPE-TSC with aggregation induced emission (AIE) characteristic is synthesized for detecting Hg²⁺ by attaching thiosemicarbazide (TSC) unit into tetraphenylethylene (TPE) group. TPE-TSC exhibits intense green emission in DMSO/H₂O (V:V?=?1:9) solution with the formation of the aggregation. TPE-TSC shows outstanding fluorescence quenching toward Hg²⁺ over other metal ions due to the formation of complex TPE-TSC/Hg²⁺ with a 2:1 binding ratio. The detection limit of TPE-TSC for Hg²⁺ is 1?×?10^?5 mol·L^?1.     

Turn‐On Fluorescence in Tetra‐NHC Ligands by Rigidification through Metal Complexation: An Alternative to Aggregation‐Induced Emission

Two tetraphenylethylene (TPE) bridged tetraimidazolium salts, [H₄ L ‐Et](PF₆)₄ and [H₄ L ‐Bu](PF₆)₄, were used as precursors for the synthesis of the dinuclear Ag^I and Au^I tetracarbene complexes [Ag₂( L ‐Et)](PF₆)₂, [Ag₂( L ‐Bu)](PF₆)₂, [Au₂( L ‐Et)](PF₆)₂, and [Au₂( L ‐Bu)](PF₆)₂. The tetraimidazolium salts show almost no fluorescence (Φ _F<1 %) in dilute solution while their NHC complexes display fluorescence “turn‐on” (Φ _F up to 47 %). This can be ascribed to rigidification mediated by the restriction of intramolecular rotation within the TPE moiety upon complexation. DFT calculations confirm that the metals are not involved in the lowest excited singlet and triplet states, thus explaining the lack of phosphorescence and fast intersystem crossing as a result of heavy atom effects. The rigidification upon complexation for fluorescence turn‐on constitutes an alternative to the known aggregation‐induced emission (AIE).     

Optical Properties and Photo‐Oxidation of Tetraphenylethene‐Based Fluorophores

We report the optical properties of tetraphenylethene (TPE) and other TPE derivatives functionalised with an octyl group (TPE‐OCT) and polyethyleneglycol group (TPE‐PEG) in the side chain. We compared TPE‐OCT and TPE‐PEG with TPE in both organic solvents and under aqueous conditions. All materials exhibit aggregation‐induced emission, however, uncommonly, TPE‐PEG seems to aggregate in aqueous solution with enhanced photoluminescence quantum efficiency (PLQE) relative to that in organic solvents. All three materials can be photo‐oxidised in solution to their diphenylphenanthrene derivative by irradiation with UV light (at both ≈1 and ≈5 mW cm^?2), with a subsequent enhancement in PL efficiency. The electron‐donating ether group increases the rate of oxidation relative to bare TPE and also photo‐oxidation was shown to be solvent and concentration dependent. Finally, photo‐oxidation was also demonstrated in the aggregate state.     

A 1,3‐Indandione‐Functionalized Tetraphenylethene: Aggregation‐Induced Emission,Solvatochromism, Mechanochromism,and Potential Application as a Multiresponsive Fluorescent Probe

A tetraphenylethene (TPE) derivative substituted with the electron‐acceptor 1,3‐indandione (IND) group was designed and prepared. The targeted IND‐TPE reserves the intrinsic aggregation‐induced emission (AIE) property of the TPE moiety. Meanwhile, owing to the decorated IND moiety, IND‐TPE demonstrates intramolecular charge‐transfer process and pronounced solvatochromic behavior. When the solvent is changed from apolar toluene to highly polar acetonitrile, the emission peak redshifts from 543 to 597 nm. IND‐TPE solid samples show an evident mechanochromic process. Grinding of the as‐prepared powder sample induces a redshift of emission from green (peak at 515 nm) to orange (peak at 570 nm). The mechanochromic process is reversible in multiple grinding–thermal annealing and grinding–solvent‐fuming cycles, and the emission of the solid sample switches between orange (ground) and yellow (thermal/solvent‐fuming‐treated) colors. The mechanochromism is ascribed to the phase transition between amorphous and crystalline states. IND‐TPE undergoes a hydrolysis reaction in basic aqueous solution, thus the red‐orange emission can be quenched by OH^? or other species that can induce the generation of sufficient OH^?. Accordingly, IND‐TPE has been used to discriminatively detect arginine and lysine from other amino acids, due to their basic nature. The experimental data are satisfactory. Moreover, the hydrolyzation product of IND‐TPE is weakly emissive in the resultant mixture but becomes highly blue‐emissive after the illumination for a period by UV light. Thus IND‐TPE can be used as a dual‐responsive fluorescent probe, which may extend the application of TPE‐based molecular probes in chemical and biological categories.     

Exploring the interactions between gold nanoparticles and analytes through surface‐assisted laser desorption/ionization mass spectrometry

Surface‐assisted laser desorption/ionization mass spectrometry (SALDI‐MS) is applied to provide strong evidence for the chemical reactions of functionalized gold nanoparticles (Au NPs) with analytes – Hg²⁺ ions induced MPA?Au NPs aggregation in the presence of 2,6‐pyridinedicarboxylic acid (PDCA) and H₂O₂ induced fluorescence quenching of 11‐MUA?Au NDs. PDCA‐Hg²⁺‐MPA coordination is responsible for Au NPs aggregation, while the formation of 11‐MUA disulfide compounds that release into the bulk solution is responsible for H₂O₂‐induced fluorescence quenching. In addition to providing information about the chemical structures, SALDI‐MS is also selective and sensitive for the detection of Hg²⁺ ions and H₂O₂. The limits of detection (LODs) for Hg²⁺ ions and H₂O₂ by SALDI‐MS were 300 nM and 250 µM, respectively. The spot‐to‐spot variations in the two studies were both less than 18% (50 sample spots). Our results reveal that SALDI‐MS can be used to study analyte‐induced changes in the surface properties of nanoparticles. Copyright © 2010 John Wiley & Sons, Ltd.     

A New Tetraphenylethylene‐Derived Fluorescent Probe for Nitroreductase Detection and Hypoxic‐Tumor‐Cell Imaging

The fluorescence detection of nitroreductase (NTR) and evaluation of the hypoxia status of tumor cells are vital, not only for clinical diagnoses and therapy, but also for biomedical research. Herein, we report the synthesis and application of a new fluorometric “turn‐on” probe for the detection of NTR ( TPE?NO₂ ) that takes advantage of the aggregation‐induced emission of tetraphenylethylene. TPE?NO₂ can detect NTR at concentrations as low as 5 ng mL^?1 in aqueous solution. The detection mechanism relied on the aggregation and deaggregation of tetraphenylethylene molecules. Moreover, this fluorescent probe can be used to monitor the hypoxia status of tumor cells through the detection of endogenous NTR.     

Aggregation‐Induced Emission and Aggregation‐Promoted Photo‐oxidation in Thiophene‐Substituted Tetraphenylethylene Derivative

Aggregation‐induced emission combined with aggregation‐promoted photo‐oxidation has been reported only in two works quite recently. In fact, this phenomenon is not commonly observed for AIE‐active molecules. In this work, a new tetraphenylethylene derivative (TPE‐4T) with aggregation‐induced emission (AIE) and aggregation‐promoted photo‐oxidation was synthesized and investigated. The pristine TPE‐4T film exhibits strong bluish‐green emission, which turns to quite weak yellow emission after UV irradiation. Interestingly, after solvent treatment, the weakly fluorescent intermediate will become bright‐yellow emitting. Moreover, the morphology of the TPE‐4T film could be regulated by UV irradiation. The wettability of the TPE‐4T microcrystalline surface is drastically changed from hydrophobic to hydrophilic. This work contributes a new member to the aggregation induced photo‐oxidation family and enriches the photo‐oxidation study of tetraphenylethylene derivatives.     

White‐Light Electroluminescence with Tetraphenylethylene as Emitting Layer of Aggregation‐Induced Emissions Enhancement

Tetraphenylethylene (TPE) based molecules with easy synthesis, good thermal stability, and especially their aggregation‐induced emissions enhancement (AIEE) effect recently become attractive organic emitting materials due to their potentially practical application in OLEDs. Herein, the AIEE behaviors of tetraphenylethylene dyes (TMTPE and TBTPE) were investigated. Fabricated luminesent device using TMTPE dye as emitting layer displays two strong emitting bands: the blue emission coming from the first‐step aggregation and the yellow emission attributed to the second‐step aggregation. Thus, it can be utilized to fabricate the white‐light OLEDs (WOLEDs) of the single‐emitting‐component. A three‐layer device with the brightness of 1200 cd·m^?2 and current ef?ciency of 0.78 cd·A^?1 emits the close to white light with the CIE coordinates of x=0.333 andy=0.358, when applied voltage from 8–13 V, verifying that the TPE‐based dyes of AIEE effect can be effectively applied in single‐emitting‐component WOLEDs fabrication.     

Dimedone‐decorated conjugated polymer: Tandem knoevenagel‐michael post‐modification synthesis and its application as optical probe for Hg2+ and ClO− in high‐water‐fraction mediums

High‐efficiency, mild‐conditioned tandem Knoevenagel–Michael reaction was utilized to post‐modify aldehyde‐containing, triphenylamine‐based precursor conjugated polymer ( CP1 ) to afford dimedone‐decorated aimed polymer ( CP2) . The chemical structure of CP2 was verified by FTIR and ¹H NMR analyses. With the introduction of aqueous Hg²⁺, fluorescence of CP2 in THF‐water mixture (V _THF/V _water = 1/100) (buffered with 5 mM sodium dihydrogen phosphate‐disodium hydrogen phosphate (PB), pH = 7.4) altered significantly, with the emission changed from blue to orange. Besides this, CP2 also displayed specific optical response to ClO^? in another probing medium (V _THF/V _water = 1/100, buffered with 50 mM PBS (with NaCl in PB, pH = 7.4). The detailed probing process and the plausible detection mechanism of CP2 to Hg²⁺ and ClO^? were systematically investigated here. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1067–1076     

Synthesis and Design of Aggregation‐Induced Emission Surfactants: Direct Observation of Micelle Transitions and Microemulsion Droplets

The direct visualization of micelle transitions is a long‐standing challenge owing to the intractable aggregation‐caused quenching of light emission in the micelle solution. Herein, we report the synthesis of a surfactant with a tetraphenylethene (TPE) core and aggregation‐induced emission (AIE) characteristics. The transition processes of surfactant micelles and the microemulsion droplets (MEDs) formed by the surfactant with a TPE core were clearly visualized by a high‐contrast fluorescence imaging method. The fluorescence intensity of the MEDs decreased as the size of MEDs increased as a result of weakening of the restriction of intramolecular rotation (RIR). The results of this study deepen our understanding of micelle‐transition processes and provide solid evidence in favor of the hypothesis that the AIE phenomenon has its origin in the RIR of fluorophores in the aggregate state.     

A Strategy for Dramatically Enhancing the Selectivity of Molecules Showing Aggregation‐Induced Emission towards Biomacromolecules with the Aid of Graphene Oxide

By intelligently utilizing the different interacting strengths between different moieties according to the displacement method, general biosensors with aggregation‐induced emission (AIE) characteristics for biomacromolecules without selectivity were converted to excellent, highly selective probes for one specific biomacromolecule with the aid of graphene oxide (GO) in an aqueous medium. Importantly, thanks to the different interactions between the AIE molecule and biomacromolecules, just by simply changing the AIE molecule the sensing system could detect different types of biomacromolecules, thereby providing a new approach to the development of AIE‐based sensors with high selectivity and sensitivity. More specifically, the complex of A₂HPS?HCl—a derivative of hexaphenylsilone (HPS) functionalized by two amino (A₂) groups (N(CH₂CH₃)₃)—and GO only gives an “off–on” response to DNA, with a detection limit of 2.3 μg mL^?1 toward DNA‐CT (calf thymus); interestingly, the complex of TPE‐N₂C₄ (1,2‐bis{4‐[4‐(N,N,N‐triethylammonium)butoxy]phenyl}‐1,2‐diphenylethene dibromide) and GO could only detect the presence of bovine serum albumin (BSA), whereas other biomacromolecules, including DNA, RNA, and even other proteins have very little influence.     

Aggregation‐Induced Emission Characteristics of o‐Carborane‐Functionalized Tetraphenylethylene Luminogens: The Influence of Carborane Cages on Photoluminescence

Tetraphenylethylene (TPE)–carborane hybrids are constructed, and the impact of carborane substituents on the aggregation‐induced emission (AIE) characteristics of TPE‐cores has been investigated. When altering the 2‐R‐group on the carborane unit with ‐H, ‐CH₃ or phenyl group, the luminescent quantum yield of the corresponding TPE derivatives can be manipulated from 0.18 to 0.63 in the solid state. The emission color exhibits an obvious 100 nm shift (from blue to yellow).     

Aggregation‐Induced Emission‐Active 1,4‐Dihydropyridine‐Based Dual‐Phase Fluorescent Sensor with Multiple Functions

A N‐2‐phenylethyl‐substituted 1,4‐dihydropyridine derivative (NDHP) containing 5,5‐dimethylcyclohexane‐1,3‐dione and naphthylethylene was designed and synthesized. NDHP acts as a multifunctional fluorescent sensor in dual phases. The crystal structure analysis confirms that the NDHP molecules have highly twisted conformations. The twisted conformation results in aggregation‐induced emission properties and solid‐state emission, by restricting the intramolecular free rotation in the aggregated or solid state. In the solid state, NDHP exhibits reversible mechanochromic properties as a result of the transition between the amorphous and crystalline states. NDHP also exhibits a rare phenomenon of acid‐fumed solid‐state emission enhancement owing to the change in packing mode from a zigzag arrangement to J‐aggregation. The solid‐state stimuli‐responsive fluorescence switching is applied to realize a rewritable optical recording media and a multiple output combinational logic system. In solution, NDHP shows a selective fluorescence response for environmentally harmful Hg²⁺, with a limit of detection of 2.7 nm . This results from the “turn‐on” responsive behavior owing to the Hg²⁺‐triggered aggregation of the NDHP molecules. NDHP is also used in the imaging of intracellular Hg²⁺ in HeLa cells. These findings provide a feasible and attractive route for developing multifunctional fluorescent sensors for use in dual phases.     

Aggregation‐Induced Emission of Platinum(II) Metallacycles and Their Ability to Detect Nitroaromatics

Two new acceptors containing platinum–carbazole ( 1 ) and platinum–triphenylamine ( 2 ) backbones with bite angles of 90° and 120°, respectively, have been synthesised and characterised. Reactions of the rigid acceptor 1 with linear dipyridyl‐based donors ( 3 and 4 ) generated [4+4] self‐assembled molecular squares ( 5 and 6 ), and similar treatments with acceptor 2 instead of 1 yielded [6+6] self‐assembled molecular hexagons ( 7 and 8 ). The metallacycles were characterised by multinuclear NMR spectroscopy (¹H and ³¹P) and ESI‐MS. The geometries of the metallacycles were optimised by using the PM6 method. When aggregates of the metallacycles were formed by adding hexane solutions in dichloromethane, aggregation‐induced emission was observed for metallacycles 5 and 7 , and aggregation‐caused quenching was observed for metallacycles 6 and 8 . The formation of aggregates was verified by dynamic light scattering and TEM analyses. Macrocycles 5 and 7 are white‐light emitters in THF. Moreover, their high luminescence in both solution and the solid state was utilised for the recognition of nitroaromatic explosives.     

Meta‐linked and para‐linked water‐soluble poly(arylene ethynylene)s with amino acid side chains: Effects of different linkage on Hg2+ ion sensing properties in aqueous media

Water‐soluble, meta‐ and para‐linked poly(arylene ethynylene)s containing L ‐aspartic acid‐functionalized fluorene units (P1 and P2) and their model compounds (M1 and M2) have been synthesized, and their photophysical properties and fluorescent sensing properties were investigated in aqueous solution. P1 and M1 with the meta‐linkage show blue‐shifted absorption and emission spectra, and decreased photoluminescence quantum yields compared with those of P2 and M2 with para‐linkage. Their absorption and fluorescence spectra are pH dependent perhaps due to the aggregation of the polymer chains at low pH values. In buffer solutions, both polymers and their model compounds exhibit the excellent selectivity and sensitivity to Hg²⁺ over other common metal ions. Furthermore, the quenching constant and detection limit of P1 are determined to be 1.04 × 10⁷ M^?1 and 10 nM, and show the higher sensitivity compared to P2. Further comparison of their model compounds reveal that the sensitivity and quenching efficiency of M1 is also higher than that of M2, indicating that the meta‐linkage pattern plays a key role in improving their Hg²⁺ ion sensing properties. In addition, both meta‐ and para‐linked polymers exhibit the higher quenching efficiency than their model compounds due to the amplified fluorescence response of conjugated polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A tetraphenylethene based polarity dependent turn-on fluorescence strategy for selective and sensitive detection of Hg in aqueous medium and in living cells

A turn-on fluorescent chemosensor strategy based on the change in the polarity of aggregation induced emission active tetraphenylethene is presented for the detection of Hg²⁺ in aqueous medium and in living cells. The sensing mechanism involves the formation of nonpolar fluorescent aggregates of tetraphenylethene molecules by elimination of polar moieties of TPE with Hg²⁺ interaction.     

In vivo Visualization of the Process of Hg2+ Bioaccumulation in Water Flea Daphnia carinata by a Novel Aggregation‐Induced Emission Fluorogen

This paper employs a specially designed aggregation‐induced emission fluorogen (AIEgen) to in vivo visualize the process of Hg²⁺ bioaccumulation in a common species of freshwater zooplankton Daphnia carinata (D. carinata) by two methods, direct Hg²⁺ absorption and ingestion of Hg²⁺ contaminated food. We analysed the relevance between photoluminescence (PL, I₅₉₅/I₄₈₀) ratios and Hg²⁺ (C_Hg2+) and developed the master curve for Hg²⁺ determination based on measuring the PL intensity of the solution. Meanwhile, fluorescent image analysis showed that the major recipient organs of Hg²⁺ in D. carinata were the compound eyes and carapace, followed by the intestine and shell gland, but not the brain or heart. The response of D. carinata to Hg²⁺ via uptake from surrounding water differed distinctly from that through food intake of the algae (Euglena gracilis) contaminated by mercury. When Hg²⁺ was encapsulated by algae membrane, no fluorescence was detected, and the carapace morphology remained intact after ingesting algae for 80 min, in contrast to the rapid carapace deformation by direct Hg²⁺ absorption. The D. carinata showed higher mortality by direct Hg²⁺ immersion than via food ingestion. The reason for the high mortality after Hg²⁺ immersion was possibly due to carapace deformity after chemical reaction between chitin and mercury, but the biochemical pathway leading to morality needs further study.     

Solid‐State Emissive Aroyl‐S,N‐Ketene Acetals with Tunable Aggregation‐Induced Emission Characteristics

N‐Benzyl aroyl‐S,N‐ketene acetals can be readily synthesized by condensation of aroyl chlorides and N‐benzyl 2‐methyl benzothiazolium salts in good to excellent yields, yielding a library of 35 chromophores with bright solid‐state emission and aggregation‐induced emission characteristics. Varying the substituent from electron‐donating to electron‐withdrawing enables the tuning of the solid‐state emission color from deep blue to red.     

Water‐soluble hyperbranched polyelectrolytes with high fluorescence quantum yield: Facile synthesis and selective chemosensor for Hg2+ and Cu2+ ions

New water‐soluble hyperbranched polyfluorenes bearing carboxylate side chains have been synthesized by the simple “A2 + B2 + C3” protocol based on Suzuki coupling polymerization. The linear polyfluorene analogue LPFA was also synthesized for comparative investigation. The optical properties of the neutral precursory polymers in CHCl₃ and final carboxylic‐anionic conjugated polyelectrolytes in buffer solution were investigated. The obtained hyperbranched polyelectrolyte HPFA2 with lower content of branch unit (2%) showed excellent solubility and high fluorescence quantum yield (?_F = 89%) in aqueous solution. Fluorescence quenching of HPFA2 by different metal ions was also investigated, the polyelectrolyte showed high selectivity for Hg²⁺ and Cu²⁺ ions relative to other various metal ions in buffer solution. The Stern‐Volmer constant K_sv was determined to be 0.80 × 10⁶ M^?1 for Hg²⁺ and 3.11 × 10⁶ M^?1 for Cu²⁺, respectively, indicating the potential application of HPFA2 as a highly selective and sensitive chemosensor for Hg²⁺ and Cu²⁺ ions in aqueous solution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3431–3439, 2010