Aggregation-induced Emission Enhancement Phenomenon Research Articles

Solvent-induced modulation of sensitivity and selectivity in the self-assembly of tetracationic cyclophanes with cholesterol sulphate, sodium dodecyl sulfate, and sodium dodecyl benzene sulfonate: Observations of significant shifts

Cyclophane CP-1 demonstrates markedly distinct sensitivities toward Cholesterol sulfate (CH-S), Sodium Dodecyl Sulfate (SDS), and Sodium Dodecyl Benzene Sulfonate (SDBS) when the solvent is shifted minimally from a 95 % to a 98 % HEPES-DMSO mixture. In a 98:2 HEPES-DMSO mixture, CP-1 engages in highly selective self-assembly with CH-S, which is characterized by aggregation-induced emission enhancement (AIEE) in contrast to other steroidal sulfates such as pregnenolone sulfate (PRG-S), dehydroisoandrosterone sulfate (DIAND-S), taurocholic acid (TACH-S), and the surfactants SDS and SDBS. This assembly results in an approximate 40-fold increase in fluorescence intensity with three equivalents of CH-S and allows for the detection of concentrations as low as 200 nM under physiological conditions. Dynamic light scattering (DLS) studies illustrate the aggregation of CP-1 and CH-S, with the zeta potential of each shifting from negative values to nearly zero in a 1:2 CP-1:CH-S mixture, indicating self-assembly. This aggregation behavior is reversible, as demonstrated by a corresponding decrease and then increase in fluorescence intensity with temperature variations from 25 °C to 70 °C and back to 25 °C. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses show that CP-1 forms aggregates ranging from 100 to 180 nm, which increase to 150–250 nm upon interaction with CH-S. In a 95:5 HEPES-DMSO mixture, CP-1 exhibits a stronger AIEE response with SDS and SDBS compared to CH-S. Cyclophane CP-2, when dissolved in binary DMSO-water mixtures with water content exceeding 80 %, shows similar AIEE phenomena and undergoes selective fluorescence quenching with SDS and only a 50 % increase in fluorescence intensity with CH-S, irrespective of the HEPES concentration (95 % or 98 %).

Aggregation induced emission enhancement of [Ag3Cu8] clusters protected by alkyne and phosphane ligands

In this work, three isostructural clusters of [Ag3Cu8(R-Ph-CC)6(N-triphos)2(Ph2PO2)3](NO3)2 (R = 4-H (1), 4-CH3 (2), 4-F (3)) were successfully synthesized and structurally determined by single crystal X-ray diffraction. At room temperature, they show weak photoluminescence in CH2Cl2 solution at ∼715 nm but with a 20-fold increase of quantum yields in their aggregation. Crystallographic and Hirshfeld surface analysis reveals a plentiful of intermolecular interactions (C−H…N, C−H…O, C−H…π, π…π) exist in their solid states, which can inhibit the intra-/inter-molecular motions (vibration and rotation) and thus generate the aggregation induced emission enhancement phenomenon. Moreover, their solid luminescent intensities at 100 K are much higher than those at room temperature. Comparisons of their luminescence show that the substituents on the para-positions of phenylethynes not only have a charge effect on emission, but also have steric effect on the molecular stacking and supramolecular interactions in the aggregated and crystalline states, and then on the aggregation-induced emission. The density functional theory (DFT) calculations show that the possible luminescence mechanism of these clusters is ligand-to-metal−metal charge transfer (LMMCT).

Nobiletin with AIEE Characteristics for Targeting Mitochondria and Real-Time Dynamic Tracking in Zebrafish.

Nobiletin is a natural product with multiple physiological activities and is the main ingredient of Pericarpium Citri Reticulatae. We successfully discovered that nobiletin exhibits aggregation induced emission enhancement (AIEE) properties and it has significant advantages such as a large Stokes shift, good stability and excellent biocompatibility. The increase in methoxy groups endows nobiletin a greater fat-solubility, bioavailability and transport rate than the corresponding unmethoxylated flavones. Ulteriorly, cells and zebrafish were used to explore the application of nobiletin in biological imaging. It emits fluorescence in cells and is specifically targeted at mitochondria. Moreover, it has a noteworthy affinity for the digestive system and liver of zebrafish. Due to the unique AIEE phenomenon and stable optical properties of nobiletin, it paves the way for discovering, modifying and synthesizing more molecules with AIEE characteristics. Furthermore, it has a great prospect with regard to imaging cells and cellular substructures, such as mitochondria, which play crucial roles in cell metabolism and death. Indeed, three-dimensional real-time imaging in zebrafish provides a dynamic and visual tool for studying the absorption, distribution, metabolism and excretion of drugs. In this article, more directions and inspiration can be presented for the exploration of non-invasive pharmacokinetic research and intuitive drug pathways or mechanisms.

Synthesis of Fluorophore Based Functional Material for Selective Detection of Al3+ Ion in Water and Decoding the AIEE Property of Its Hydrosol.

A designed aggregation-induced emission enhancement (AIEE) active fluorescence probe 2,3-Bis-[(2-hydroxy-napthalen-1-ylmethylene)-amino]-but-2-enedinitrile (L) was synthesized via one step condensation method. The probe shows swift sensitivity and selectivity toward Al3+over other relevant metal ions and also exhibits significant AIEE phenomena in methanol/water mixture. Significant enhancement of fluorescence intensity is triggered via chelation-enhanced fluorescence through complex (Al3+-L) formation. A 2:1 metal to ligand ratio is observed from Job's plot based on UV - Vis absorption titration and detection limit (LOD) is found as low as 31.14nM. Moreover, 1H NMR titrations and fluorescence reversibility by adding Al3+ and EDTA sequentially had been performed to establish the binding site of sensor complex (Al3+-L). Time-resolved photoluminescence, dynamic light scattering, optical microscopy, and on-site visualization studies have been performed to understand the AIEE mechanism of L in different volume percentage of water and methanol mixture. An INHIBIT molecular logic gate has been constructed utilizing the fluorescence behavior of the probe, L in presence of Al3+ and strong chelating ligand EDTA.

Fluorescence Sensing of pH and p-Nitrophenol Using an AIEE Active Pyridoxal Derived Schiff Base.

An easy-to-prepare aggregation-induced emission enhancement (AIEE) active Schiff base NPY was synthesized by condensing vitamin B6 cofactor pyridoxal with 3-hydroxy-2-naphthoic hydrazide, and employed for the fluorescent sensing of pH and p-nitrophenol (p-NP). The AIEE phenomenon of NPY was investigated in mixed DMSO/H2O medium. The weakly yellow-fluorescent NPY (λem = 535nm) in pure DMSO turned to a bright cyan-fluorescent NPY (λem = 490nm) upon addition of poor solvent water. The DLS and SEM analyses supported the self-aggregation of NPY that restricted the intramolecular rotation and activated the excited state intramolecular proton transfer (ESIPT) process. The AIEE luminogen (AIEEgen) NPY containing 90% of water fraction (fwater) was employed for the fluorescent sensing of pH. AIEEgen NPY displays three distinct fluorescent pH windows: non-fluorescent below pH 3.0 and above pH 10.0, cyan fluorescent between pH 3.0 to 8.0, and yellow fluorescent between pH 8.0 to 10.0. AIEEgen NPY was also applied for the detection of nitroaromatics in HEPES buffer (10% DMSO, 10 mM, pH 7.0). The addition of p-NP selectively quenched the fluorescent intensity of AIEEgen NPY with an estimated detection limit of 1.73 µM. The analytical utility of AIEEgen NPY was examined by quantifying p-NP in different real water samples.

Alkynyl-Protected Ag12Cu4 Cluster with Aggregation-Induced Emission Enhancement

Photoluminescence (PL) of atomically precise metal clusters is attractive for various applications, including light emission, chemical sensing, and bioimaging. Herein, we report the synthesis and total structure of an alkynyl-protected bimetallic AgCu cluster, Ag12Cu4(C≡CR)14(PPh3)4 (Ag12Cu4: HC≡CR = 3,5-bis(trifluoromethyl)phenylacetylene; PPh3 = triphenylphosphine), which exhibits crystallization-induced emission enhancement and aggregation-induced emission enhancement phenomena. As revealed by the single crystal X-ray diffraction data, the Ag12Cu4 cluster comprises an octahedron Ag6 core, which is stabilized by two large Ag3Cu2(C≡CR)7(PPh3)2 metal–ligand motifs. The free valence electron count suggests that Ag12Cu4 is a two-electron superatom. Interestingly, the weak PL of Ag12Cu4 solution at ≈730 nm (near-infrared region) is found to be significantly enhanced in the solid state (15 and 8 fold respectively, for the crystalline and aggregated forms). A detailed structural analysis of the Ag12Cu4 cluster reveals the presence of abundant intercluster C–H···F interactions, which significantly restrict the intramolecular rotations and vibrations, leading to strong PL enhancement in the solid state. This work will trigger the studies of other alloy metal nanoclusters with promising photophysical properties for optoelectronic and other applications.

Importance of the donor unit on fluoranthene for selective detection of nitro aromatic explosives

In this work, two aggregation-induced emission enhancement (AIEE) materials encompassing phenyl (M1) and thiophene (T1) units flanked to fluoranthene were synthesized. We report a new packing polymorphic phase of M1 and the molecular interactions in the crystal lattice were stabilized by CH···π (2.882 Å) interactions. Single crystal X-ray diffraction (SXRD) studies revealed that high torsional angles of phenyl/thiophene unit on the fluoranthene endow weak π-π intermolecular interactions in the crystal lattice. The photophysical properties of M1 and T1 were explored in solution, solid-state and their AIEE phenomenon was studied in THF/water systems. Both the compounds show strong sky-blue emission at 453 nm (M1) and 460 nm (T1). The fluorescence lifetime and quantum yields are varied significantly in the aggregated form. The emission enhancement ascribed due to restricted intramolecular rotation (RIR) of thiophene/phenyl with central π-conjugated fluoranthene in the aggregation state. Distinct changes in the surface morphology, variation in the photophysical properties and energy levels by varying the THF/water ratios furnish its potential towards trace detection of different nitroaromatics. Both materials show high sensitivity and selectivity towards detection of Trinitrophenol (TNP), however, T1 showed a high quenching rate constant at fw = 90 % (KSV = 5.81 × 104 M−1) with LOD of 0.6 ppm at fw = 70 %. The observed fluorescence quenching is attributed due to photoinduced electron transfer from fluoranthene to nitroaromatics through static quenching process. The remarkable efficiency of these fluorescent probes were further explored towards the analysis of river/tap water samples, suggesting their high potential for use in field analysis.

Ultrafast Aggregation-Induced Tunable Emission Enhancement in a Benzothiadiazole-Based Fluorescent Metal-Organic Framework Linker.

Aggregation-induced emission enhancement (AIEE) is a process recently exploited in solid-state materials and organic luminophores, and it is explained by tight-molecular packaging. However, solution-phase AIEE and its formation mechanism have not been widely explored. This work investigated AIEE phenomena in two donor-acceptor-donor-type benzodiazole-based molecules (the organic building block in metal-organic frameworks) with an acetylene and phenyl π-conjugated backbone tapered with a carboxylic acid group at either end. This was done using time-resolved electronic and vibrational spectroscopy in conjunction with time-dependent density functional theory (TD-DFT) calculations. Fluorescence up-conversion spectroscopy and time-correlated single-photon counting conclusively showed an intramolecular charge transfer-driven aggregate emission enhancement. This is shown by a red spectral shift of the emission spectra as well as an increase in the fluorescence lifetime from 746 ps at 1.0 × 10-11 to 2.48 ns at 2.0 × 10-3 M. The TD-DFT calculations showed that a restricted intramolecular rotation mechanism is responsible for the enhanced emission. The femtosecond infrared (IR) transient absorption results directly revealed the structural dynamics of aggregate formation, as evident from the evolution of the C≡C vibrational marker mode of the acetylene unit upon photoexcitation. Moreover, the IR data clearly indicated that the aggregation process occurred over a time scale of 10 ps, which is consistent with the fluorescence up-conversion results. Interestingly, time-resolved results and DFT calculations clearly demonstrated that both acetylene bonds and the sulfur atom are the key requirements to achieve such a controllable aggregation-induced fluorescence enhancement. The finding of the work not only shows how slight changes in the chemical structure of fluorescent chromophores could make a tremendous change in their optical behavior but also prompts a surge of research into a profound understanding of the mechanistic origins of this phenomenon. This may lead to the discovery of new chemical strategies that aim to synthesize novel chromophores with excellent optical properties for light-harvesting applications.

HAPPY Dyes as Light Amplification Media in Thin Films.

A series of 1H amorphous tri-phenyl pyridine (HAPPY) dyes have been synthesized from luminescent triphenyl-group-containing 2-methyl-6-styryl-substituted-4H-pyran-4-ylidene derivatives in reactions with benzylamine and investigated for suitability as solution-processable light-emitting medium components in thin films for amplified spontaneous emission (ASE). Conversion of a 4H-pyrane ring into a 1H-pyridine fragment enables aggregation-induced emission enhancement (AIEE) behavior in the target products and slightly increases thermal stability, glass transition temperatures, and ASE efficiency with PLQY up to 15% and ASE thresholds as low as 46 μJ/cm2 in neat spin-cast films, although thermal and photophysical properties are mostly dominated by the incorporated electron acceptors. Continued lasing parameter efficiency parameter improvement experiments revealed that no further optimization of HAPPY dyes by doping in polymer matrixes is required as the amplified spontaneous emission thresholds were lowest in pure neat films due to the AIEE phenomenon.

On-site monitoring of thiram via aggregation-induced emission enhancement of gold nanoclusters based on electronic-eye platform

The rapid and on-site monitoring of thiram is of great significance because the residue of thiram in agriculture has caused great contamination in environment and food, as well as threaten to the human health. Herein, we constructed a fluorometric strategy for on-site monitoring thiram via the aggregation-induced emission enhancement (AIEE) effect of glutathione-capped gold nanoclusters (GSH-AuNCs). The dissociated Ag+ ions can effectively enhance the fluorescent emission intensity of GSH-AuNCs at 570 nm owing to the AIEE phenomenon. Upon the addition of thiram, the fluorescence enhancement effect was weakened due to the strong coordinative interaction between Ag+ and thiram. By monitoring the signal change, the thiram residues were quantitatively analyzed with the detection limit of 0.05 μg mL−1. Notably, a home-made electronic-eye (E-eye) system, containing of a test-strip and a smartphone, was constructed as a portable platform to recognize and quantitatively analyze thiram in 10 min on the basis of captured fluorescence signals from a test strip with immobilized probe by direct photographing, which provides a direct quantitative tool to identify pesticide. Taking advantage of user-friendliness, portability and simplicity, the E-eye system are expected to fulfill the demand for quantitative on-site testing of pesticide especially in resource-limited areas.

Synthesis and photophysical investigation of 2-hydroxyquinoline-3-carbaldehyde: AIEE phenomenon, fluoride optical sensing and BSA interaction study

Nowadays compounds showing aggregation-induced emission enhancement (AIEE) are extensively studied due to their huge range of applications in material science. AIEE and the anion recognition ability of 2-hydroxyquinoline-3-carbaldehyde (1) were explored. Unique AIEE phenomenon is observed in CH3CN with water as the cosolvent and the highest emission was noted in the solvent volume ratio 2:8 (CH3CN: H2O). The compound is a selective time dependent turn on fluoride ion sensor in acetonitrile medium with a distinct color change from colorless to yellow, fabricating it as a visible sensor. Ion sensing ability was monitored through UV–vis, steady state emission, life time studies and 1H NMR spectroscopy. The limit of detection of fluoride ion is 4.09 × 10−6 M. Moreover the compound exhibited notable quenching of fluorescence intensity with bovine serum albumin. Thus small molecule like the quinoline motif can be used in extensive applications in the scientific research.

A novel AIEE polymer sensor for detection of Hg2+ and Ag+ in aqueous solution

A novel AIEE (aggregation-induced emission enhancement)-active conjugated polymer incorporating thiazole and tetraphenylethene (TPE) was designed and synthesized via Pd-catalyzed Sonogashira coupling reaction. The polymer shows typical AIEE phenomena, and emits green fluorescence in the mixed solvent of tetrahydrofuran (THF) and water, reaching a maximum fluorescence intensity when the fraction of water is 90%. In the aqueous phase (fw = 90%), the polymer sensor exhibits “turn-off” fluorescence quenching responses towards Hg2+ and Ag+ over other cations, such as Li+, K+, Ca2+, Mg2+, Ba2+, Zn2+, Cd2+, Co2+, Ni2+, Pb2+, Cu2+, Al3+ and Fe3+. The obvious fluorescence change (bright yellow to weak emission) can be clearly observed by the naked eyes.

Synthesis of 13-substituted derivatives of berberine: Aggregation-induced emission enhancement and pH sensitive property

Abstract Five kinds of berberine derivatives with hydroxy, methyl, ethyl, benzyl and (4-methyl)benzyl group at 13-position have been synthesized and characterized. 13-hydroxyberberine chloride exhibits aggregation-induced emission enhancement (AIEE) property because of hydroxy group, which is beneficial to increase the rigidity of molecule by enlarging conjugated system. Optical properties in pure solution, CH3OH/H2O mixed solution, amorphous and crystalline state were comparatively investigated. Polymeric morphology and particle size of 13-hydroxyberberine chloride with different water fractions (0–90 vol%) were obtained by scanning electron microscope (SEM) and dynamic light scattering (DLS) method respectively, which provided reasonable explanation that the formation of small globular nanoparticles in mixed solution is conducive to the fluorescence emission. The single crystal structure of 13-hydroxyberberine chloride was determined by single-crystal X-ray diffraction. Crystallographic data indicated that the main mechanism of the AIEE phenomenon is the existences of J-aggregation (head to tail dipole stacking) combined with molecular planarization. The calculation done by DFT showed that the HOMO–LUMO bandgap is in accordance with experimental data. To further explore the biomedical application of 13-hydroxyberberine, its cell viability and cell imaging performance were examined, which demonstrate that 13-hydroxyberberine shows definite fluorescent intensity. In all, 13-hydroxyberberine should be a promising candidate for different biomedical application such as pH fluorescence probe because of its response to the stimuli of pH value.

A dual photoluminescence enhancement system: stabilization of a water soluble AIEE fluorogen using silver nanowire.

This manuscript describes the preparation of water soluble aggregation-induced emission enhancement (AIEE)-based fluorescent organic nanoparticles (FONs). The fluorescence diversity of the FONs was investigated in the presence of silver nanowires. We observed that the emission of the FONs can be enhanced by mixing with the nanowires, which is believed to originate from resonance between the emission of the FONs and the surface plasmon resonances of the metal surface. That is, the AIEE phenomenon was promoted according to the metal-enhanced fluorescence (MEF) mechanism that can be used to build up a novel double emission enhancement (DEE) platform and to extend the range of AIEE applications. The systemic fluorescence enhancement, lifetime and photostability were measured and the AIEE-MEF evaluation and the interaction between the FONs and nanowires were discussed based on the obtained spectral data and SEM and fluorescent microscopy images.

Alkoxy substituted D-π-A dimethyl-4-pyrone derivatives: Aggregation induced emission enhancement, mechanochromic and solvatochromic properties

Three series of D-π-A 2,6-dimethyl-4-pyrone-cored derivatives were designed and synthesized. Evaluation by spectroscopic methods indicated that all the compounds exhibited aggregation-induced emission enhancement (AIEE) effect and solvatochromism. The experimental results revealed that the restriction of intramolecular rotation is the key element for showcasing the AIEE phenomenon. Moreover, all of the compounds presented red-shifted mechanochromic behavior, the extent of the red-shift was mainly dependent on the position and length of alkoxyl group. The PXRD and DSC profiles demonstrated a transformation from crystalline to amorphous state upon grinding. The D-A strategy introduced in this work could facilitate the development and application of ingenious mechanochromic materials.

New cyano functionalized silanes: aggregation‐induced emission enhancement properties and detection of 2,4,6‐trinitrotoluene

Two novel tetrahedral silicon‐centered cyano functionalized silanes, namely bis(4‐cyanophenylethynyl)dimethylsilane (CN-1) and bis(4‐cyanophenylethynyl) diphenylsilane (CN-2), have been synthesized and well characterized. They demonstrated unusual aggregation‐induced emission enhancement (AIEE) properties in the H‐type aggregation state with nanoparticle aggregate formation. Further study shows that the 4‐cyanophenylethynyl unit is the structure base to induce the AIEE phenomenon and the silicon core may enhance the AIEE effect. By single‐crystal analysis, the twisted tetrahedral conformation of silicon core and restricted intramolecular motions are speculated as the AIEE mechanism for these unusual H‐type aggregates of CN-1 and CN-2. Moreover, both CN-1 and CN-2 show an obvious fluorescent quenching response to 2,4,6‐trinitrotoluene (TNT) in THF solution, making them promising candidates in the application of explosive detection. Copyright © 2013 John Wiley & Sons, Ltd.

Aggregation-induced emission enhancement based on 11,11,12,12,-tetracyano-9,10-anthraquinodimethane

By introducing phenyl groups into the 2- and 6-positions of 11,11,12,12-tetracyano-9,10-anthraquinodimethane, a material (dP-TCAQ) with aggregation-induced emission enhancement (AEE) characteristics was synthesized. The AEE phenomenon was explained by analysis of its solid-state packing mode. To our best knowledge, this is the first report regarding 11,11,12,12-tetracyano-9,10-anthraquinodimethane with AEE behaviour.

Aggregation-Induced Emission Enhancement of Aryl-Substituted Pyrrole Derivatives

The relationship between the structures and light emission properties of five aryl-substituted pyrrole derivatives was studied during aggregation in THF-water mixtures. Only pentaphenylpyrrole clearly shows, however, an aggregation-induced emission enhancement (AIEE) phenomenon. On comparison of the optical properties and single-crystal structures of these pyrrole derivatives, it is suggested that the more twisted configuration which prevented parallel orientation of conjugated chromophores combined with the restricted intramolecular rotation (RIR) effect was the main cause of the AIEE phenomenon.

Synthesis of blue light emitting bis(triphenylethylene) derivatives: A case of aggregation-induced emission enhancement

A series of new aggregation-induced emission enhancement derivatives from bis(triphenylethylene) with strong blue-light-emitting properties and high thermal stability have been synthesized. Their maximum fluorescence emission wavelengths range between 464–468 nm, with fluorescence quantum yields of 0.58–0.88. Their glass transition temperatures range from 125 °C to 178 °C. The obtained experimental results demonstrate the different aggregation-induced emission enhancement phenomena caused by the effect of solvent and formation of both H- and J- aggregation states. An emitting device was fabricated using a bis(triphenylene) derivative in the emitting layer which exhibited a luminance efficiency of up to 2 cd/A with a maximum brightness of 548 cd/m 2.

New Carbazole-Based Fluorophores: Synthesis, Characterization, and Aggregation-Induced Emission Enhancement

A series of new carbazole-based luminophores (1-12) were synthesized and well characterized, which demonstrated aggregation-induced emission enhancement (AIEE) properties. The obtained experimental results demonstrated that the attachment of aromatic rotors to luminophore moieties would lead to the decreased quantum yields (measured in diluted solutions); the more rotors attached, the smaller the quantum yields tested. This further confirmed that the AIEE phenomena were caused by the restriction of the intramolecular vibrational and rotational motions in an indirect manner.